Verbal Descriptions of Mechanism Diagrams - ACS Publications

Article Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX

pubs.acs.org/jchemeduc

Compromised Structures: Verbal Descriptions of Mechanism Diagrams Gautam Bhattacharyya* and Michael S. Harris Department of Chemistry, Missouri State University, 421 Temple Hall, 901 South National Avenue, Springfield, Missouri 65897, United States ABSTRACT: We report our research of seven pairs of students enrolled in the second semester of sophomore-level organic chemistry as they attempted to describe (in their own words) and draw, respectively, three electron-pushing diagrams of threestep reaction mechanisms. The tasks’ objective was to accurately reproduce the diagrams based solely on the mechanistic language descriptions, because the goals of this research were to identify characteristics of effective descriptions and to describe factors that impede students in constructing those descriptions. Both members of each pair had at least one opportunity to describe and one to draw. To eliminate nonverbal communication the students were unable to see each other but were free to ask questions to their partners. Though most of the groups were able to successfully replicate the diagrams, they struggled to describe and draw chemical structures. Instead of falling back on the IUPAC system of nomenclature, they used iconic symbols and geometric shapes to characterize the structures. The participants were able to communicate the positioning of the curved arrows of the electron-pushing formalism with relative ease. The main instructional implications are that students need (1) intensive help with constructing and using Lewis structures and (2) scaffolding with explanations that gradually transition from explicit aspects of diagrams to the implicit, deeper ones. KEYWORDS: Second-Year Undergraduate, Chemical Education Research, Organic Chemistry, Collaborative/Cooperative Learning, Communication/Writing, Mechanisms of Reactions FEATURE: Chemical Education Research asserts that students “do what we want them to do without knowing what we want them to know.” (See ref 2, p 18.) More closely related to the current research, Flynn and colleagues have studied “mechanistic language descriptions” as students worked on two different types of EPF tasks.18,19 After learning the EPF, but prior to instruction on specific reactions, the students used the curved arrows to (1) describe the flow of electrons, (2) identify atoms of the reactant(s) onto the product(s), (3) follow changes in charges, and (4) express their reasoning for mechanistic steps (even when that was not an explicit part of a task).18 The authors observed that, though the students focused on charges, they tended to treat them like objects and not connect them to the electron movement. Additionally, students seemed overwhelmed with trying to use curved arrows to simultaneously keep track of electron and atom movement. When they investigated mechanistic language descriptions of students after receiving instruction on chemical reactions, Flynn and Featherstone found that the research participants still seemed to struggle with using the EPF to concurrently track electron and atom movement.19 The students also did not use techniques, such as redrawing structures including implicit hydrogen atoms and nonbonding electron pairs, that were taught in class to help solve EPF-based tasks. Taken together, these two studies seem to indicate that keeping track of atoms and electron pairs in mechanism diagrams may push the limits

T

eaching reactions is at the core of instruction in sophomore-level organic chemistry, and the primary means of doing so is with mechanisms expressed diagrammatically using the electron-pushing formalism, EPF, like that in Figure 1.1 (Unless otherwise noted, “mechanism” without any modifiers will refer to electron-pushing mechanisms, not those derived from kinetic data.) Though items for assessing electronpushing may primarily be expressed diagrammatically,2,3 teaching continues to incorporate verbal and diagrammatic external representations (ERs) of EPF mechanisms. When they work complementarily, the combination of words and diagrams can be highly effective instructional tools.4 Ainsworth proposes that, for learners to reap the benefits of that synergy, translation between ERs is one of the necessary, underlying skills.4 The potential importance of electron-pushing to students’ success in the year-long, sophomore-level organic chemistry sequence, Organic I and Organic II, has been recognized in chemical education research as evidenced by a number of studies published over the past decade.1,5−17 Many of the students’ problem-solving and conceptual difficulties that this body of research brought to light were recently reviewed by Graulich, who identified two “big picture” themes arising from her analysis of the literature.2 First, students seem, for the large part, unable to transfer much of their general chemistry knowledge into organic chemistry courses. As such, students may have sufficient understanding of a concept but may apply that in an inappropriate context. Second, students are often missing the implicit knowledge needed to understand how to apply concepts and models to various tasks. As a result, Graulich © XXXX American Chemical Society and Division of Chemical Education, Inc.

Received: February 22, 2017 Revised: November 7, 2017

A

DOI: 10.1021/acs.jchemed.7b00157 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

Article

Figure 1. Sample diagram of an electron-pushing mechanism.

children but a tool for moving or storage for adults (ref 23, p 52). More importantly, meaning cannot be inherent to “things”, or symbols, since their significance is the outcome of communications among the individuals. Del Carlo’s example that different groups of individuals could attribute different meanings to the same symbol is particularly relevant to this study since it accommodates the possibility that instructors and students could develop separate meanings for the same set of symbols. For example, the inscription that could mean cyclohexane to a practicing chemist could mean just a hexagon to students. Scholars of symbolic interactionism have suggested that Blumer’s second principle, language as the medium by which meaning is negotiated between individuals, was heavily influenced by his mentor, George Herbert Mead.22,24 Mead proposed that the very act of naming an object confers meaning to it. The final principle, thought, describes the process by which humans interpret meaning and, as needed, modify their personal conceptions of the symbol whose meaning is being negotiated.

of students’ cognitive load, i.e., the capacity of their working memories. Recently, we studied how Organic II students translated verbal descriptions of mechanisms (excerpted from their textbook) into the corresponding diagrams.20 We also gave the students tasks in which they were asked to describe EPF diagrams without and with the curved arrows. The participants’ approach to the course was to memorize EPF diagrams while disregarding any of the related verbal ERs. As such, they treated the verbal → diagram tasks as if they were more like typical electron-pushing tasks and attempted to complete them on that basis. When comparing the students’ descriptions of the diagrams without and with the EPF arrows, the students, like those in Flynn and colleagues’ research, primarily used the EPF as an attentional tool for electron and atom movements. Overall, the participants had a difficult time with the diagram description tasks in our translation study. As such, we had little insight into the types of verbal descriptions that could help students accurately translate between ERs of EPF mechanisms. We report our research of Organic II students as they attempted to describe and draw, respectively, EPF diagrams. This study was guided by the following questions: • What characteristics are common to students’ mechanistic language descriptions of multistep EPF diagrams that other Organic II students can use to reproduce those diagrams? • What features present the most significant challenges for Organic II students to successfully communicate and reproduce those diagrams? We used “mechanistic language description” to remain consistent with Flynn’s designation of the activity. As used in this context, the descriptions’ “success” will be based on the extent to which drawn diagrams resemble the originals.

■

Participants and Setting

Participants were recruited at a publically funded, comprehensive university in the midwestern United States. After receiving approval from the Institutional Review Board (IRB), we solicited voluntary participation of Organic II students during the tenth week of the Spring, 2015, semester. The course instructor anticipated covering at least some reactions of all the major functional groups by that point. We purposely sampled25 the students from this course in that we sought pairs who interacted with each other, either as study partners or in some other capacity, outside of a formal learning environment. This way, we hoped that the students would have a better chance of understanding each other’s vernacular or any idiosyncratic speech patterns. In addition to explaining information associated with study participation we mentioned that each student would receive a $25 VISA gift card upon study completion. Seven dyads, consisting of nine women and five men, volunteered for this research. Only one of the pairs was mixed-gender. The participants’ grades roughly corresponded to the class-wide grade distribution, except that no one in our sample received a grade below a C. There are three potential limitations to our sampling method. First, the corresponding author taught Organic I to 10 of the students. Second, there was a larger proportion of women among the participants than there was in the course. Third, the familiarity among the students in each pair may have resulted in unique patterns of communication. We believe that we minimized idiosyncrasies arising from the final limitation by drawing conclusions based on patterns of data across all of the groups. Other potential limitations are discussed at the end of this section.

METHODS

Theoretical Framework

This study was guided by symbolic interactionism which Herbert Blumer defined using the following premises (see ref 21, p 2): • “[H]uman beings act toward things on the basis of the meanings that the things have for them. • [T]he meaning of such things is derived from, or arises out of, the social interaction that one has with one’s fellows. • [T]hese meanings are handled in, and modified through, an interpretive process used by the person in dealing with the things he [or she] encounters.” In Blumer’s characterization, “things” are not limited to tangible objects; they include abstract constructs. Contemporary theorists have condensed Blumer’s “core principles” into the phrase “meaning−language−thought”.22 Meaning attributed to symbols can range from the mundane to the most complex of ideas. Del Carlo, for example, explained that cardboard boxes may mean material for making a fort to

Data Collection

Del Carlo noted that it is important for the data to include the “interaction” aspect of symbolic interactionism, i.e., collected in B



Article

Figure 2. Electron-pushing mechanisms which were described and reproduced by the dyads. The words in italics did not appear in the students’ copies; they were used for the data analysis as described below. (Please note that the stereochemical configuration of C-2 of Intermediate 2 in Task 3 is incorrect. We have left the diagram unchanged because it was the diagram the students were given.).

circumstances where participants are able to use and communicate with the “symbols” being studied.22 On the basis of the “meaning−language−thought” principle of interaction we needed to have a protocol in which one person could use language to share his or her mechanistic language descriptions (or his or her meaning for the symbols in this study) and the other interacting individual could draw an interpretation of the description as a way to externalize, or publically express, his or her interpretations of the partner’s words. It is for these reasons that we asked one member of each pair to describe an electronpushing diagram and the other to try to reproduce it on paper. We chose the mechanisms in Figure 2 because they all had three steps, incorporated a variety of structural attributes (including stereogenic centers), and were confirmed by the course instructor to be of appropriate content and difficulty.

Each pair was interviewed once during which time both members had at least one opportunity to describe and one to draw. So that we could best elucidate verbal descriptions of these diagrams the students were unable to see each other but were free to ask questions of each other. After deciding among themselves who would assume each of the roles for the first task, the partner describing the mechanism was reminded that the goal was for the drawer to be able to reproduce the mechanism based solely on his or her utterances. The interviewer remained silent during this period other than to answer participants’ questions, all of which were procedural in nature. For example, some participants asked if they were close enough to the video-recording device. After both members of the pair decided that they were finished with the task, they were asked to compare the drawing with the printed diagram. C



Article

The interviewer also used that time to debrief each student. Additionally, each member of the pair was given the opportunity to offer comments about the task, the study, or even their experiences learning organic chemistry. The entire interview protocol is provided in Box 1. These exchanges contributed to

One of our main concerns for analyzing the drawings was to pinpoint errors as precisely as possible. Consider the following example in which Alana (Group 6) drew the first mechanistic step of Task 1 (Figure 3A). Although Alana’s starting material was incorrectly drawn, a side-by-side comparison with the original (Figure 3B) indicates that the curved arrows in both, from oxygen lone pairs to protons, and the respective products, both containing protonated oxygen atoms, were consistent with her partner Chloe’s description as shown in the following exchange: Chloe: “Since oxygen has two lone pairs you are going to add a hydrogen to one of the lone pairs by attacking the hydrogen with a lone pair.” Alana: “So the lone pair is attacking the hydrogen?” Chloe: “Yeah, okay you know have a positive charge on oxygen right?” Alana: “Wait so do I need to redraw the structure?” Chloe: “No you just have a positive charge. Yeah when you redrew it and you have an H coming off of the oxygen.” An example representative of a different type of error is shown in Figure 4A. Though the double bond was misplaced in the structure of the starting material, the group was able to correct the mistake because Olivia (Group 3) described Intermediate 1 from “scratch”. (Contrast this approach with that of Chloe in the previous example who described the intermediate in terms of the reactant with a modification.) In this case, the electron-pushing and intermediate were correctly drawn though the reactant was not. Another error type, shown in Figure 4B, resulted from an incorrectly drawn product but correctly drawn reactant and electron-pushing. These examples indicated that each step had to be parsed into reactant−electron-pushing−product to better identify the locus of an error. (The italicized terms in Figure 2 reflect the breakdown of each mechanism.) Furthermore, the first example with Alana and Chloe demonstrated that each drawn component would have to be evaluated alongside the partner’s description. Thus, the presence of each item was recorded with a star, as will be shown in the Results and Discussion section. Using this scheme, the electron-pushing for the first step and the first intermediate in Alana’s (Group 6) drawing would receive stars because both were consistent with her partner Chloe’s words. The cell for the starting material, however, would be left empty. Continuing the data analysis, we used the ChemDraw files of the students’ work to deconstruct each drawing into the components as indicated in Figure 2 and paired those components with the corresponding descriptions. The second author marked each group’s drawing for Task 1 and then met with the first author to review his scoring decisions. After the

Box 1. Interview Protocol (1) Please describe the diagram below in enough detail that your partner is able to reproduce it. You may use whatever language you deem appropriate. (2) Please take a moment and compare the diagram you drew with the one you were given. How do you think you did? (3) What was the hardest part to describe? Why? What was the easiest to describe? Why? (Follow-up questions were asked about what prompted the person to describe it in that way.) (4) What the hardest part to draw? Why? What was the easiest to draw? Why? (5) After looking at the printed diagram, is there something you wish you had described differently? Why? If applicable: What makes you think you should have done [name of difference] differently? (6) After looking at the printed diagram, is there something you wish your partner had described differently? Why? Do you wish you had asked for a clarification or missing piece of information? Why? If applicable: What makes you think you should have done [name of difference] differently? (7) Would either of you like to add something about this or the task(s) before that we have not covered? negotiating meanings of the symbols since the participants discussed why their interpretations did or did not match. The remaining tasks were similarly completed with the describer and drawer from the first mechanism switching roles for the second. For the third task, the pair was allowed to decide who would assume each role. The interviews were audio-taped using a digital voice recorder and video-recorded using an iPad. To protect the participants’ anonymity, only their hands and drawings appear in the video clips. Data Analysis

The voice recordings were transcribed verbatim, and the videos were subsequently used to annotate the transcripts. To help further maintain the participants’ anonymity their diagrams were redrawn as ChemDraw files.26

Figure 3. (A) Alana’s (Group 6) rendition of the first step of Task 1. (B) The first step as given to the participants. D



Article

Figure 4. Drawing errors made by Group 3. (A) In Task 2, the location of the bromonium ion in the product of the step is opposite its location in the reactant. (B) An extra negative charge is added to a carbon in the product of the step.

We divided the Task 1 data by group and subsequently met to discuss the coding results. One of the most important things that emerged from this coding step was that the nature of drawers’ difficulties seemed to correspond to those of the speakers. For example, drawing chemical structures was the most difficult part of the task for speakers and drawers, even though each may have been referring to different structures. We decided, therefore, to frame the codes from the standpoint of the speaker since the ultimate goal of the research was to identify potentially effective descriptions of mechanisms. Since the data for the other two tasks had not been analyzed, we combined our respective dimensions to generate the initial coding scheme (Table 1). The dimension “Specific ordering of words, i.e., syntax” emerged from a combination of categories such as “participant said nucleophile first” and “electrophile as sentence object”. There were also a couple of categories that did not fit into either of the predetermined codes, so we just gave them their own codes. After the second author used this scheme as guide for analyzing the data for the remaining tasks, he proposed several changes to the initial coding scheme. Since the first author concurred that all of these were well-represented (or not in some cases) in the data, all of the revisions were incorporated into the final coding scheme. For example, the speakers used geometric figures to describe intermediates and other species in the other two tasks. As such, we added the dimension “Geometric shapes”. Furthermore, the starting material in Task 3 exposed a difficulty for explaining stereochemistry that appeared limited to acyclic systems. Instead of adding a new dimension, we just broadened “Difficulty describing tertiarybutyl groups and tertiary-butyl cations” to “Difficulty describing specific structural features”. Finally, the difficulties the students appeared to have with some of the proton-transfer steps labeled “unanalyzed chunks” in the initial coding scheme (Table 1)in Task 1 did not seem to recur in the other two tasks. Furthermore, the comments about imagistic reasoning were limited to members of only two groups and, as such, are not really descriptive of the current data. Because there was a significant possibility that these two codes were artifacts of

researchers reached a consensus over any differences of interpretation, the second author completed marking Tasks 2 and 3. For analysis of the transcript data, the diagram and corresponding verbal description for each component that received a star in Table 3 were separated into two sets: one for Table 1. Initial Coding Scheme Code Characteristics of successful electron-pushing descriptions

Strategies for successfully describing structures Difficulties with describing chemical structures

Unanalyzed chunks Imagistic reasoning

Dimensions Identify atom(s) of nucleophile that will bond with the electrophile Identify atom(s) of electrophile that will bond with the nucleophile Specific ordering of words, i.e., syntax Points of reference Iconic symbols Difficulty describing starting material(s) Difficulty describing tertiary-butyl groups and tertiary-butyl cations Did not use IUPAC nomenclature Difficulty describing proton-transfer steps Speaker and drawer spoke of needing to mentally image diagram

substances (starting materials, intermediates, or products) and the other set for the curved arrows for the mechanistic steps. The data pairs for the components that did not receive a star were similarly divided. Instead of using “open coding”,27 we used a bottom-down approach using the guiding research questions to formulate main codes. As such, the transcripts were searched for the following: • Characteristics of mechanistic language descriptions leading to successful reproduction of a diagram by another student. • Participants’ perceptions of most difficult parts of diagrams to either describe or draw. Though the major codes may have been predetermined, the specific dimensions of each one emerged from the transcript analysis. E



Article

Communicating the positions of the curved arrows, by contrast, was relatively easy. Weston later explained his difficulty with describing the starting material: “Um, I guess just knowing where to start when describing it. I mean do you start with this carbon here [referring to leftmost carbon]? Or do you start with the oxygen and, you know, build on each side of it?” The dilemma expressed in this quote is noteworthy because participants in our mechanism problem-solving studies also asserted that knowing where or how to begin was the toughest part of completing a task.5,9 The students’ struggles in the current study may, at least to an extent, also help explain the difficulties faced by the participants in our previous research. The troubles describing starting materials were greatly exacerbated by the stereochemical features of the one in Task 3. Because of the acyclic, or open-chain, carbon skeleton, the drawer would have had to know the specific orientation of the zigzag, carbon−carbon backbone to correctly capture the three-dimensional orientation of the asymmetric carbons. The difficulty with the stereocenters did not arise in the previous task because of the constraints afforded by the cyclohexane ring, as implied by Ethan (Group 4) toward the end of the interview: “The one before that like with the six-membered ring that’s easy to describe what comes off there [pointing to the cyclohexane ring].” Without using the IUPAC R,S system for designating configuration of stereocenters, however, those describing Task 3 were unable to accurately communicate the structure of the starting material. Beyond stereochemistry, the students avoided using IUPAC nomenclature throughout the tasks, even though it would have greatly simplified what turned out to be the ordeal of describing the various substances in the mechanisms. Consider the following exchange with Ethan and Caleb (Group 4) in the context of Task 3: Interviewer: “Do you think it would be useful or not to use IUPAC nomenclature?” Ethan: “I think me and Caleb are on the same page. We could have done it [referring to use of the IUPAC system] but it’s just easier to say four carbon chain coming off of the second or third rather than 2,3 oxy...” Caleb: “Yeah or 2,3 cis blah blah blah... No just the whole going back to the stereochemistry. If he would have said cis and that all at the beginning I would have been more confused.” This exchange demonstrated using the IUPAC system of nomenclature was predicated on the dexterity of both members of the pair with the formalism. It is important to note here that the interview prompt specifically asked students to use “their own words” to describe the electron-pushing diagrams. Especially in light of this prompt, we did not expect the participants to spontaneously use IUPAC nomenclature to describe chemical structures. Our point is, however, that despite the significant effort that the speakers put in to explain the structures, none of them resorted to IUPAC nomenclature in the face of that challenge. Interestingly, the interviewer inadvertently mentioned use of the IUPAC system of nomenclature to Group 5 after Task 2 (instead of after Task 3). Nonetheless, Rose went through the laborious process of attempting to describe the starting material for Task 3 without using the nomenclature system.

Table 2. Final Coding Scheme Code Characteristics of successful electron-pushing descriptions

Strategies for successfully describing structures

Difficulties with describing chemical structures

Dimensions Identify atom(s) of nucleophile that will bond with the electrophile Identify atom(s) of electrophile that will bond with the nucleophile Specific ordering of words, i.e., syntax Points of reference Iconic symbols Geometric shapes Difficulty describing starting material(s) Difficulty describing specific structural features Did not use IUPAC nomenclature

the instrument and specific participants, respectively, both were removed for the final coding scheme (Table 2). Limitations of the Study

One of the main limitations of this study is that the tasks incorporated three polar mechanisms limited to a handful of functional groups. Mechanisms of one of the carbonyl functionalities were not included, nor were those of radical or pericyclic reactions. Furthermore, this study did not address the students’ understanding of these mechanisms. As such, we cannot predict the full impact that potentially more comprehensible mechanistic language descriptions might have on student learning and performance. These and many other factors are left to future investigations.

■

RESULTS AND DISCUSSION Table 3 shows results from rating all of the drawings along with the pseudonyms for each participant and their roles in each task. Data in Table 3 show that the groups did quite well with all the tasks, but were nearly flawless with Task 2. None of the groups were able to correctly reproduce the absolute stereochemical configurations of the starting material in Task 3. Those who were given the stars for it in Table 3 had the appropriate connectivity and relative configurations. As previously stated, “meaning” in the symbolic interactionism context does not imply a certain level of understanding.22 In the presentation of results that follows, “meaning” will usually be inferred from students’ utterances based on their viewing of either the given or drawn image. We use the participants’ verbatim quotes to support our claims in the presentation of the results. Annotations in square brackets are used to provide context or clarification. Troublesome Structures

The fundamental difficulty for the students related to their ability to recreate structural representations of the chemical species. Depending upon the task and the group, each pair spent about 80 to 90% of their time attempting to reproduce reactant(s), product(s), and intermediates. Interestingly, all of the participants singled out describing the starting material as the toughest part of each task, as exemplified by Ava’s (Group 2) comment about the most difficult aspect of describing Task 2: “Probably setting up the initial molecule; like getting all the pieces in the right place.” As another example, Weston (Group 3) similarly spoke about Task 1: “I guess just initially describing what the molecule looked like; the starting material here. The first reactant. Um, the arrows themselves didn’t seem hard to explain at all.” F



Article

Table 3. Groups’ Performance Reproducing the Diagramsa,b Component Speaker Drawer Starting Material Step 1 Intermediate 1 Step 2 Intermediate 2 Step 3 Product 1 Product 2

Group 1 Hudson Zach ☆ ☆ ☆ ☆ ☆ ☆ ☆ ☆

Group 2 Rochelle Ava ☆

☆ ☆ ☆ ☆ ☆

Speaker Drawer Starting material Step 1 Intermediate 1 Step 2 Intermediate 2 Step 3 Product 1

Zach Hudson ☆ ☆ ☆ ☆ ☆ ☆ ☆

Ava Rochelle ☆ ☆ ☆ ☆ ☆ ☆ ☆

Speaker Drawer Starting material Step 1 Intermediate 1 Step 2 Intermediate 2 Step 3 Product 1

Zach Hudson

Ava Rochelle ☆c ☆ ☆ ☆ ☆ ☆ ☆

☆ ☆ ☆

Group 3 Task 1 Weston Olivia ☆ ☆ ☆ ☆ ☆ ☆ Task 2 Olivia Weston ☆ ☆ ☆ ☆ ☆ ☆ Task 3 Weston Olivia ☆c ☆ ☆ ☆

☆

Group 4

Group 5

Group 6

Group 7

Caleb Ethan ☆ ☆ ☆ ☆ ☆ ☆ ☆ ☆

Rose Elsie

Chloe Alana

☆ ☆

☆ ☆

Tara Julie ☆ ☆ ☆ ☆ ☆ ☆ ☆ ☆

☆ ☆

Ethan Caleb ☆ ☆ ☆ ☆ ☆ ☆ ☆

Elsie Rose ☆ ☆ ☆ ☆ ☆ ☆ ☆

Alana Chloe ☆ ☆ ☆ ☆ ☆ ☆ ☆

Julie Tara ☆ ☆ ☆ ☆ ☆ ☆ ☆

Ethan Caleb ☆c ☆ ☆ ☆ ☆ ☆ ☆

Rose Elsie

Chloe Alana ☆c ☆ ☆ ☆ ☆ ☆ ☆

Julie Tara ☆c ☆ ☆ ☆ ☆ ☆ ☆

☆ ☆ ☆ ☆ ☆

a

Each star indicates that the Drawer correctly reproduced that aspect of the respective diagram. The legends for the tasks are in Figure 2. bEmpty boxes indicate that the student did not correctly draw this aspect of the respective diagram. cStudent did not draw the correct absolute stereochemistry of the starting material.

Figure 5. Task 1 starting material as described by two of the participants.

Alternate Strategies

this point by explaining how he chose to describe the starting material in Task 1: “I decided to start with the oxygen and build on each side. It’s the only one that’s different. It’s the only heteroatom there. So everything in that molecule’s identical besides; well the atoms at least besides the oxygen.”

The participants used three strategies, either alone or in combination, to successfully describe molecular structures. One of these strategies was to create descriptions around reference points in structures, especially those of the starting materials. Weston (Group 3) followed his earlier comments to G



Article

“Um to know like which are the new bonds being formed and the other ones breaking like where those electrons were coming from.” The three parts of successful descriptions were the following: (1) identification of the source of electrons as a nonbonding or bonding pair, (2) concomitant specification of the atom(s) from which the curved arrow originated, and (3) designation of the atom receiving the pair of electrons. Furthermore, each of the descriptions had the same order of terminology, i.e., nucleophile → active voice action verb → electrophile. Equally important, the descriptions of those who were unsuccessful conveying the correct sequence of curved arrows were missing one or more of the components mentioned in the previous sentences. These characteristics are exemplified in Ava’s (Group 2) description of the second step of Task 2: “So you’re going to draw an arrow from the oxygen lone pair [referring to that of the previously mentioned water molecule] to the carbon that has the methyl coming off of it and then you are going to have another arrow that is showing the bond from the second carbon the bond between the second carbon and the bromine you are going to show it the arrow coming from that to the Br.” In another example, Alana (Group 6) explained their success with the final task: “She [Chloe] described it the way it looked. Also what was happening. ‘Oh like the negatively charged oxygen attacks the third carbon.’ And I was like, ‘Oh okay.’ A lot more straightforward, instead of like, ‘The electron somewhere attacks the carbon.’ What carbon was it?” Additionally, the synergy, and thereby necessity, provided by all three factors was captured in the following exchange between Hudson (Speaker) and Zach (Group 1) regarding Step 2 of Task 1: Hudson: “And then it looks like the oxygen leaves.” Zach: “OK, so how exactly does it leave?” Hudson: “It looks like it takes the electrons from its bond with carbon.” Zach: “Which carbon?” Hudson: “The central, the, uh, tert-butoxide carbon. Yeah, and you’re left with the um, three, the butoxide, or the tertbutoxide group with the hydrogen on it. That make sense?” Zach: “Wait. I thought you said it, the, it took electrons from...” Hudson: “It, it leaves as methanol. You should have methanol and your carbon group and now the carbon group will be positive. You generate a carbocation.” Zach: “Yeah. I gotcha.” Later, during the debriefing period after the task, Zach reiterated “In the second step when an alcohol is leaving through a heterolysis step; it was difficult, at least from the way Hudson was describing it, to determine where the electrons; or which electrons from which bond were pushing. Like I wasn’t sure if a methanol was being formed or if tert-butanol was being formed, essentially. What Hudson said that finally made me understand; he said it was the electrons that came from the carbon−oxygen bond and it was the carbon that was part of the tert-butyl group.” The vignette demonstrates the importance of the feedback loop created between the two students. The question-and-answer interactions allowed Zach to request information whose importance or relevance Hudson may not have initially realized.

Though he never mentioned it, “build[ing] on each side” could have also had a cognitive-load-reducing effect. In Task 2, the clearer reference point, the cyclohexane ring, for describing the starting material may be one of the reasons for the pairs’ near-universal success. Conversely, the groups who incorrectly drew the starting material in Task 1 used ambiguous reference points. In fact, both unsuccessful groups tried to describe a 4-carbon chain with an oxygen in place of the second carbon (Figure 5). Note that the structures are consistent with the respective descriptions, both of which had a degree of vagueness to them. In a second approach, participants used iconic symbols to successfully communicate structures of chemical substances. In Task 1, Weston (Group 3) at one point characterized the tertiary-butyl moiety as a “chicken leg”. Similarly, Tara (Group 7) used “bird leg” for the same substituent. As another example, four of the participants (from Groups 2, 4, 5, and 6) described the numbering of the carbon atoms of the cyclohexane ring in a clockwise orientation when explaining the location of the methyl group on the cyclohexane ring in Task 2. Consider the following representative quote from Elsie (Group 5): “Alright. Ready? Start with a six carbon ring. Now off it you start with the top one, top carbon is number one then going on the second one you have a methyl group now between the second and the third carbon on the ring you have a methyl bond. Alkene sorry.” Note that in her instruction to draw a “six carbon ring” Elsie never asked Rose to draw it so that the apex was pointing to the top of the page. Yet, her subsequent numbering, “starting at the top” was predicated on a specific orientation of the hexagon, which all four of the drawers in these groups spontaneously did. When later asked to explain her reasoning for numbering the carbon atoms, Elsie stated, “To me it’s just easier to go like with a clock and have that kind of reference point.” Rose echoed this sentiment, “It’s just more familiar. We are just used to it; like the clock ‘cause we look at the clock everyday so.” The successful use of iconic symbols is an example of the (unique) meanings that can arise out of social interactions, one of the fundamentals of symbolic interactionism. The use of the geometric shapes was the third strategy the participants used to describe structural features. Across the board, the groups used the term “triangle” to describe the three-membered rings of Tasks Two (bromonium ion of Intermediate 1) and Three (epoxides). Additionally, Ethan (Group 4) and Alana (Group 6) used the term “hexagon” to describe the starting material of Task 2. The participants’ expedient strategies are reminiscent of Talanquer and colleagues’ considerable research on types of ad hoc, common-sense reasoning that students use in place of domain-specific reasoning and/or terminology.28 Electron-Pushing

All of the groups felt that describing or drawing the electronpushing arrows was quite easy. Recall from Weston’s first comment that he did not find “explaining the [curved] arrows” to be particularly difficult. This perception was shared across the groups. The data indicated that productive explanations consisted of three components, an overview of which was offered by Julia during the debriefing period following Task 1: H



Article

tions. First, the specific atom(s) and/or source of electrons, nonbonding or bonding pair, of the nucleophiles were explicitly identified as were the corresponding locations of the electrophiles. Second, the phrases had a nucleophile → active voice action verb → electrophile syntax in which the nucleophile and electrophile are the subject and object, respectively. The efficacy of the sentence structure may not be arbitrary since it aligns with the nucleophile-to-electrophile syntax of the EPF.20 As such, instructors might consider aligning the syntax of mechanistic language descriptions with that of the EPF as described above. This implication may seem overly simplistic, however, in many of the commonly used phrases, such as “proton transfer”: the electrophile is presented as the agent of the action. In other instances the nucleophile can be in a passive phrase, such as “[name of electrophile] is attacked by [name of nucleophile]”. During the initial stages of learning a subject with multiple representational systems, students use language cues to help create coherent meanings for the external representations.20 With respect to mechanistic language descriptions, another factor to consider is the overall level of complexity of language that is used in many published instructional materials. Elsie (Group 5) commented “Yeah, wording, bigger terms. Textbooks are notorious for that. I feel if there was more simple terms, you know explaining it like if you pulled two kids off the street and were describing it and asked them to do it the same way they would draw it. The same way.” The difficulty understanding textbooks is not limited to students in introductory-level courses. The opinions of firstyear graduate students in Advanced Organic Chemistry about their textbook were similar to that of Elsie.5 To help students learn to comprehend mechanistic language descriptions found in instructional materials, it might be necessary to gradually scaffold them, perhaps over the course of a semester, beginning with descriptions containing mostly “everyday” language and building toward descriptions laden with domain-appropriate terminology. The other implication of this research is that students need intensive work with constructing, interpreting, and naming Lewis structures. Help with naming does not necessarily mean more instruction on IUPAC nomenclature; it may be more effective to focus on names for functional groups and reaction intermediates such as “bromonium ion”. Helping students improve constructing and interpreting Lewis structures is a matter of intense investigation by several research groups because one thing that was made clear by Cooper and colleagues is that the guidelines appearing in most instructional materials are wholly inadequate.29

Alternatively, these exchanges afforded Zach the opportunity to clarify any of Hudson’s previous statements. Finally, since each of the tasks had proton-transfer steps, the students’ near-ubiquitous use of the word “hydrogen” to describe “proton” in proton-transfer steps (see, for example, Chloe’s quote in the Data Analysis section) deserves mention. In every case when speakers incorporated domain-appropriate terms such as “deprotonated” or “proton transfer”, they reverted to using “hydrogen” in a following sentence. The incorrect use of “hydrogen” can be classified as a negotiated meaning because for every such utterance the drawer wrote “H+”, instead of the domain-accepted meaning of an atom or molecule of hydrogen. Parenthetically, it should of particular concern that this inappropriate substitution of terms has been observed in graduate students in the first year of their doctoral programs.5,9,10

■

CONCLUSIONS AND IMPLICATIONS Seven pairs of Organic II students described and drew, respectively, electron-pushing diagrams of three reaction mechanisms. The speakers’ mechanistic language descriptions allowed us to elicit, at least on some level, the meanings they attributed to the diagrams, and the partners’ drawings allowed us, again at least on some level, to elicit their meaning for the speakers’ descriptions as manifested in their sketched renditions of the diagrams. In this way, we were able to address the core principles of symbolic interactionism: meaning−language−thought. Between structural representations and the curved arrows, the former posed the greater challenge to describe and draw. In addition to the total amount of time devoted to reproducing the structures, there were specific types of features that proved to be especially difficult. For example, the stereochemical configurations of the acyclic starting material (and intermediates) of Task 3 proved to be the most difficult of these; none of the groups produced structures with the correct absolute configurations. These results are consistent with Flynn’s body of research on mechanistic language descriptions,18,19 Cooper and colleagues’ research on students’ abilities to draw Lewis structures,29 and our own work with mechanistic language descriptions.20 Interestingly, all of the participants felt that the most difficult aspect of each mechanism was describing the starting material. Specifically, they did not know how or where to begin. This result could help explain consistent comments by students about their difficulties with knowing how or where to start solving a mechanism-based task.5,6,9 The students in the current study relied on three strategies to overcome the obstacles associated with communicating and reproducing the structures. First, they used reference points on the molecules, which is comparable to mapping techniques that students use in other types of problem solving in organic chemistry.6,18,19,26 Second, they used geometric figures, such as triangles, to describe features such as three-membered rings. Third, the participants used iconic symbols in a variety of ways, including characterizing a tertiary-butyl as a “chicken’s foot”. The use of iconic symbols from popular culture to successfully communicate aspects of organic chemistry diagrams provides examples of one of the fundamental assumptions of symbolic interactionism: that members of a group can negotiate unique meanings for symbols.21 In contrast, the students described the curved arrows with relative proficiency as demonstrated by the small number of errors associated with the mechanism steps (Table 3). There seemed to be two common threads to the successful descrip-

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Gautam Bhattacharyya: 0000-0001-9079-5107 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We wish to express our gratitude to the research participants for their time and efforts and the professor of the class from I



Article

(20) Bhattacharyya, G. Constructive or destructive interference? Students’ experiences with verbal and diagrammatic external representations of electron-pushing mechanisms. Manuscript submitted to J. Chem. Educ. (21) Blumer, H. Symbolic Interactionism: Perspective and Method; Prentice-Hall: Englewood Cliffs, NJ, 1969. (22) Griffin, E. A First Look at Communication Theory; McGraw-Hill: New York, 1997. (23) Del Carlo, D. Symbolic Interactionism. In Theoretical Frameworks for Research in Chemistry/Science Education Research; Bodner, G. M., Orgill, M., Eds.; Pearson: Upper Saddle River, NJ, 2007; pp 50− 71. (24) Hewitt, J. Self and Society: A Symbolic Interactionist Social Psychology, 9th ed.; Allyn & Bacon: Boston, 2002. (25) Patton, M. Qualitative Research and Evaluation Methods, 3rd ed.; Sage: Thousand Oaks, CA, 2003. (26) Bodé, N.; Flynn, A. Strategies of successful synthesis solutions: Mapping, mechanisms, and more. J. Chem. Educ. 2016, 93, 593−604. (27) Strauss, A.; Corbin, J. Basics of Qualitative Research: Grounded Theory Procedures and Techniques; Sage: Newbury Park, CA, 1990. (28) Talanquer, V. Commonsense chemistry: A model for understanding students’ alternative conceptions. J. Chem. Educ. 2006, 83, 811−816. (29) Cooper, M. M.; Grove, N. P.; Underwood, S. M.; Klymkowsky, M. W. Lost in Lewis structures: An investigation of student difficulties in developing representational competence. J. Chem. Educ. 2010, 87, 869−874.

which the participants were recruited. We would also like to thank the reviewers for helping to significantly improve this manuscript and Dr. George McBane of Grand Valley State University for his helpful comments about this research. This study was supported with start-up funds from the Office of the Provost, College of Natural and Applied Sciences, and Department of Chemistry of Missouri State University.

■

REFERENCES

(1) Bhattacharyya, G. From source to sink: Mechanistic reasoning using the electron-pushing formalism. J. Chem. Educ. 2013, 90, 1282− 1289. (2) Graulich, N. The tip of the iceberg in organic chemistry classes: How do students deal with the invisible? Chem. Educ. Res. Pract. 2015, 16, 9−21. (3) Stieff, M. When is a molecule three dimensional? A task-specific role for imagistic reasoning in advanced chemistry. Sci. Educ. 2011, 95, 310−336. (4) Ainsworth, S. DeFT: A conceptual framework for considering learning with multiple representations. Learning and Instruc. 2006, 16, 183−198. (5) Bhattacharyya, G.; Bodner, G. M. It gets me to the product”: How students propose organic mechanisms. J. Chem. Educ. 2005, 82, 1402−1407. (6) Ferguson, R.; Bodner, G. M. Making sense of the arrow-pushing formalism among chemistry majors enrolled in organic chemistry. Chem. Educ. Res. Pract. 2008, 9, 102−113. (7) Anderson, T. L.; Bodner, G. M. What can we do about Parker? A case study of a good student who didn’t “get” organic chemistry. Chem. Educ. Res. Pract. 2008, 9, 93−101. (8) Rushton, G. T.; Hardy, R. C.; Gwaltney, K. P.; Lewis, S. E. Alternative conceptions of organic chemistry topics among fourth year chemistry students. Chem. Educ. Res. Pract. 2008, 9, 122−130. (9) Kraft, A.; Strickland, A.; Bhattacharyya, G. Reasonable reasoning: Multi-variate problem-solving in organic chemistry. Chem. Educ. Res. Pract. 2010, 11, 281−292. (10) Strickland, A.; Kraft, A.; Bhattacharyya, G. What happens when representations fail to represent? Graduate students’ interpretations of organic chemistry diagrams. Chem. Educ. Res. Pract. 2010, 11, 293− 301. (11) Grove, N.; Cooper, M.; Rush, K. Decorating with arrows: Toward the development of representational competence in organic chemistry. J. Chem. Educ. 2012, 89, 844−849. (12) Grove, N.; Cooper, M.; Cox, E. Does mechanistic thinking improve student success in organic chemistry? J. Chem. Educ. 2012, 89, 850−853. (13) Cruz-Ramírez de Arellano, D.; Towns, M. H. (2014). Students’ understanding of alkyl halide reactions in undergraduate organic chemistry. Chem. Educ. Res. Pract. 2014, 15, 501−515. (14) Graulich, N. Intuitive judgments govern students’ answering patterns in multiple-choice exercises in organic chemistry. J. Chem. Educ. 2015, 92, 205−211. (15) Anzovino, M. E.; Bretz, S. L. Organic chemistry students’ ideas about nucleophiles and electrophiles: The role of charges and mechanisms. Chem. Educ. Res. Pract. 2015, 16, 797−810. (16) Anderson, J. P. Learning the language of organic chemistry: How do students develop reaction mechanism problem-solving skills? Ph.D. Dissertation, Purdue University, West Lafayette, IN, 2009. (17) Bhattacharyya, G. Trials and tribulations: Student approaches to and difficulties with proposing mechanisms using the electron-pushing formalism. Chem. Educ. Res. Pract. 2014, 15, 594−609. (18) Galloway, K.; Stoyanovich, C.; Flynn, A. Students’ interpretation of mechanistic language in organic chemistry before learning reactions. Chem. Educ. Res. Pract. 2017, 18, 353−374. (19) Flynn, A.; Featherstone, R. Language of mechanisms: Exam analysis reveals students’ strengths, strategies, and errors when using the electron-pushing formalism (curved arrows) in new reactions. Chem. Educ. Res. Pract. 2017, 18, 64−77. J


Verbal Descriptions of Mechanism Diagrams - ACS Publications

Recommend Documents