Commentary Cite This: J. Chem. Educ. 2019, 96, 1294−1297
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Construction by De-construction Gautam Bhattacharyya*
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Department of Chemistry, Missouri State University, 421 Temple Hall, 901 South National Avenue, Springfield, Missouri 65897, United States ABSTRACT: The research on how students solve electron-pushing tasks in organic chemistry suggests that students tend to memorize entire electron-pushing mechanisms as singular, indivisible units of knowledge. The research also indicates that those who can conceptualize mechanisms as collections of paradigmatic steps are more likely to solve the most challenging tasks, thus creating a need to help students learn to deconstruct these mechanisms. Individuals learning new languages exhibit an analogous behavior in which they memorize by rote entire phrases as unanalyzed chunks. Groups of words are considered unanalyzed chunks when learners can grasp the meanings of the whole phrases without necessarily understanding the constituent words. This phenomenon is most commonly associated with learning idiomatic expressions during second-language acquisition. Analyzing the chunks (i.e., breaking them down into “productive units”) is called “syntacticization”, which in the context of electron-pushing mechanisms would amount to decomposing the pathways into their constituent, paradigmatic steps. The goal of this commentary is neither to assert a definitive method for instruction in electron-pushing nor to offer an exhaustive list of strategies to help students deconstruct organic reaction mechanisms. Rather, my hope is to propose that the concepts of unanalyzed chunks and syntacticization may present a fruitful perspective to better understand how students make sense of the electron-pushing formalism. KEYWORDS: Second-Year Undergraduate, Organic Chemistry, Collaborative/Cooperative Learning, Communication/Writing, Constructivism, Mechanisms of Reactions
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sense-making as “finding a way of fitting available conceptual elements into a pattern that is circumscribed by specific constraints” (ref 6, p 10). From the sense-making7 perspective, as such, prior knowledge implicitly informs on what is cognitively possible for learners.8 During my doctoral studies with Dr. George M. Bodner of Purdue University, I began what has become a career-long interest in how students learn mechanistic reasoning using the electron-pushing formalism (EPF).9 In this commentary I describe one of our first and key findings from this work and propose how we might use research from second-language acquisition to better understand how students try to make sense of learning mechanisms using the EPF. Though I propose potential instructional strategies, my hope is to initiate a discussion about teaching and learning electron-pushing rather than professing to offer definitive solutions.
INTRODUCTION In the greater than three decades since Bodner published his now famous phrase, “Knowledge is constructed in the mind of the learner” (ref 1, p 873), its more than 1000 citations suggest that constructivism has had a significant impact on the teaching of chemistry. As a framework for teaching and learning, constructivism is a significant departure from its predecessor, behaviorism, because knowledge construction implies that learners must actively build new knowledge rather than simply receive and archive it intact from an external source. In the constructivist perspective, therefore, what one learns is dictated by what one already knows. As such, systematic study of students’ prior knowledge represents an important starting point for designing effective instructional materials because it helps reveal students’ conceptions, misconceptions, and modes of reasoning.2,3 It merits mention that learners always come with prior knowledge, even when introduced to a totally new subject. Consider, for example, the following expression of the Schrödinger equation: Ĥ Ψ = EΨ. Though it is likely that most if not all students in a general-chemistry course might not recognize the complexities represented by the Hamiltonian operator, the wave function, and the energy eigenvalue matrix, their prior knowledge of algebra could very well lead them to propose the simple, elegant, but erroneous solution that Ĥ = E.4 Thus, learners will always possess prior knowledge; however, it may be irrelevant or even counterproductive for robust knowledge construction. It is for these and other reasons that eliciting and elucidating learners’ prior knowledge is such an integral phase of successful and lasting curriculum change. Eliciting students’ prior knowledge also demonstrates how they make sense of that knowledge.5 Von Glasersfeld defines © 2019 American Chemical Society and Division of Chemical Education, Inc.
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ELECTRON-PUSHING IN ORGANIC CHEMISTRY Sixty years ago, Robert Morrison and Robert Boyd published the first edition of a textbook that revolutionized the teaching of organic chemistry.10 By combining reactions with their mechanisms, the authors helped popularize the present-day “mechanistic approach” to teaching organic chemistry, in which the EPF is used to propose likely stepwise reaction pathways.11 This method continues to be important to practicing organic chemists because mechanisms are “a way to understand, predict, and modify reactions” (ref 12, p 603). Received: July 19, 2018 Revised: April 8, 2019 Published: June 14, 2019 1294
DOI: 10.1021/acs.jchemed.8b00579 J. Chem. Educ. 2019, 96, 1294−1297
Journal of Chemical Education
Commentary
Our first study to better understand how students learned electron-pushing involved 14 graduate students enrolled in an Advanced Organic Chemistry course.9 We gave these students nine tasks in which they were provided with an entire reaction (starting materials, reagents, and products) and asked to propose electron-pushing mechanisms. An example of one of the tasks is shown in Figure 1. About half of the participants
analogous to organic-chemistry students’ rote memorization of entire mechanistic sequences. A group of words is considered an unanalyzed chunk when the learner can grasp the meaning of the whole phrase without necessarily understanding the constituent words.23 This phenomenon is most commonly the case with an idiomatic expression during second-language acquisition.24 For example, an individual may understand that the phrase “add insult to injury” means make a bad situation worse without understanding the meanings of “insult” or “injury”. Analyzing the chunks, that is, breaking them down into “productive units”, is called “syntacticization”.22 This process is given priority in language instruction for multiple reasons. First, syntacticization helps students extend their vocabularies and learn rules of grammar.25,26 Second, once broken down, the smaller pieces can be generatively used by the learner to create new expressions. Third, Skehan’s27 research showed that learners need explicit instruction to help them process formulaic language.
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Figure 1. Task from previous research in which graduate students were asked to propose electron-pushing mechanisms given the overall transformation. Reproduced from ref 9. Copyright 2005 American Chemical Society.
HELPING STUDENTS WITH SYNTACTICIZATION IN ELECTRON PUSHING In the context of electron-pushing, syntacticizing would amount to de-constructing the pathways into their constituent, paradigmatic steps, as shown above in Figure 2. There are potentially many ways to help students syntacticize electronpushing mechanisms. Klein, for example, adopts a pattern-based approach to teaching mechanisms in his Organic Chemistry textbook.28 In this case, each mechanistic step throughout the book is labeled using descriptors such as “nucleophilic attack”, “loss of leaving group”, “proton transfer”, and others (ref 28, p 260ff). A more active learning approach emerged during the course of our recent research on mechanistic language descriptions in which we asked pairs of students to describe and draw, respectively, electron-pushing diagrams like that shown in Figure 2.29 We found that this exercise helped the participants with the process of syntacticization, as shown by the following quotes: Well obviously it helps make everything more concrete when you vocalize it and your brain is expecting to work through it and grasp the concepts instead of just looking at it in a book or on a piece of paper and seeing it you have to think about what is going on to explain it or when you are expected to draw it.
readily, almost reflexively, drew the correct mechanism for the first reaction, the bromination of cyclohexene. None of them, however, could explain why any of the steps of the mechanism occurred. To borrow a term from grammar, the research participants were unable to parse their mechanisms. Behaviors in this and subsequent studies5,9,13−16 are consistent with our interpretation that students seem to memorize entire reaction mechanisms as single, indivisible units.17 They do so despite considerable efforts by their instructors encouraging students to conceptualize mechanisms as being composed of series of paradigmatic steps. The mechanism for the second reaction shown in Figure 1, for example, could be described as two “addition” steps (Figure 2). Though the students’ attempts to internalize electron-pushing mechanisms as singular cognitive entities may seem cumbersome or even incomprehensible to professors of organic chemistry, Johnstone reminds us, “What may be logical to us in retrospect, may not be so for the learner.... The insight which has broken through to us may be too ‘rich’ for a novice to digest” (ref 18, p 36). Conceptualizing mechanisms as a series of paradigmatic steps, as such, may be too “rich” for students, whereas memorizing entire mechanisms may make more sense given the status of their prior knowledge.
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Tara
I was focused on describing the mechanism rather than understanding the mechanism from the get go. And then when I was looking where was an arrow and one end of it is just pointing in mid space and I had to think about where it was coming from. And I was like, ‘Where is it even coming from?’ Is that carbon attacking the bromine? Is the carbon attacking the bond or the bond attacking the bromine? I just didn’t know, so I just had to get it by describing it.
KEY METAPHOR The comparison between learning science and learning languages is a longstanding one that was the basis of Lemke’s seminal treatise.19 More recently, Klein likened learning the formalisms and conventions to interpret and produce diagrams in organic chemistry to learning a foreign language.20,21 Perhaps, therefore, it should not be surprising that we found a phenomenon, called unanalyzed chunks or, more generally, formulaic language,22 in second-language acquisition that is
Alana
Figure 2. Electron-pushing mechanism for the reaction shown in the bottom of Figure 1. 1295
DOI: 10.1021/acs.jchemed.8b00579 J. Chem. Educ. 2019, 96, 1294−1297
Journal of Chemical Education Skagen et al.30 used activities similar to ours,29 but did so in an authentic instructional context working with students in a Canadian institution and an American institution. In their courses, the students, one from each university, were paired online. The authors reported that the activities significantly enhanced students’ knowledge of organic reactions and mechanisms. Additionally, these activities helped students develop greater confidence in their knowledge of the subject and promoted the formation of their professional identities as chemists. The use of verbalization as a means to learning is wellprecedented in constructivism.31−33 Von Glasersfeld described the reflective quality of this process: “The act of verbalization requires a review of what is to be verbalized. This review is a form of reflection and often brings to the surface inconsistencies or gaps in a train of thought” (ref 33, p 11). More recently, Talanquer suggested that by promoting greater metacognition, verbalization may help students avoid implicit assumptions and heuristic reasoning, both of which tend to lead students to scientifically invalid answers on assessments.34
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CONCLUDING THOUGHTS
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AUTHOR INFORMATION
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DEDICATION
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REFERENCES
Commentary
This manuscript is dedicated to my friend and mentor, George M. Bodner.
(1) Bodner, G. M. Constructivism: A theory of knowledge. J. Chem. Educ. 1986, 63, 873−878. (2) Bodner, G. M. Problem solving: the difference between what we do and what we tell students to do. Univ. Chem. Educ. 2003, 7, 37−45. (3) Bodner, G. M. Twenty years of learning: How to do research in chemical education. J. Chem. Educ. 2004, 81, 618−628. (4) Bodner, G. M. 2000, Purdue University, West Lafayette, IN. Personal Communication. (5) 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. (6) von Glasersfeld, E. Learning as constructive activity. Proceedings of the 5th Annual Meeting of the North American Group of Psychology in Mathematics Education, Montreal, Canada, 1983http://vonglasersfeld. com/083. (accessed March 11, 2019). (7) The term, “sense-making”, will be used in its hyphenated form in this manuscript to distinguish it from “sensemaking” as coined by Karl Weick in organizational psychology. The former is related to knowledge construction and meaning making by individuals, whereas the latter refers to the co-construction of reality by a group in an organizational setting. (8) Bransford, J.; Brown, A. L.; Cocking, R. R. How People Learn: Brain, Mind, Experience, and School; National Academies Press: Washington, DC, 1999. (9) Bhattacharyya, G.; Bodner, G. M. It gets me to the product”: How students propose organic mechanisms. J. Chem. Educ. 2005, 82, 1402− 1407. (10) Morrison, R.; Boyd, R. Organic Chemistry; Allyn and Bacon: Boston, 1959. (11) Flynn, A.; Ogilvie, W. Mechanisms before reactions: A mechanistic approach to the organic chemistry curriculum based on patterns of electron flow. J. Chem. Educ. 2015, 92, 803−810. (12) Goldish, D. M. Let’s talk about the organic chemistry course. J. Chem. Educ. 1988, 65, 603−604. (13) 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. (14) Kraft, A.; Strickland, A.; Bhattacharyya, G. Reasonable reasoning: Multi-variate problem-solving in organic chemistry. Chem. Educ. Res. Pract. 2010, 11, 281−292. (15) 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. (16) Flynn, A. How do students work through organic synthesis learning activities? Chem. Educ. Res. Pract. 2014, 15, 747−762. (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) Johnstone, A. H. Chemical education research: Where from here? Univ. Chem. Educ. 2000, 4, 34−38. (19) Lemke, J. Talking Science: Language, Learning, and Values; Ablex Publishing: Norwood, NJ, 1990. (20) Klein, D. Organic Chemistry as a Second Language: First Semester Topics, 3rd ed.; John Wiley and Sons: Hoboken, NJ, 2012. (21) Klein, D. Organic Chemistry as a Second Language: Second Semester Topics, 3rd ed.; John Wiley and Sons: Hoboken, NJ, 2012. (22) Yu, X. From memorized chunks to rule formation. A study of adult Chinese learners of English. Int. J. Appl. Linguist. Eng. Lit. 2013, 2, 98−111. (23) Tode, T. From unanalyzed chunks to rules: The learning of the English copula by beginning Japanese learners of English. Int. Rev. Appl. Linguist. 2003, 41, 23−53.
Research on students’ approaches to proposing electronpushing mechanisms to organic reactions suggests that students internalize entire pathways as single units of information.5,9,13−16 Individuals learning new languages exhibit an analogous behavior in which they memorize by rote entire phrases as unanalyzed chunks. As Yu notes, “[Second Language Acquisition] research has offered evidence indicating that some aspects of language learning (if not all) can be regarded as a process of breaking down initially unanalyzed chunks of language in long-term memory into smaller, more productive units” (ref 22, p 98). Learning the paradigmatic steps contained in electron-pushing mechanisms, therefore, may amount to knowledge construction by de-construction. Recognizing students’ tendencies to memorize entire electron-pushing sequences as unanalyzed chunks suggests that a significant portion of instruction should emphasize helping students syntacticize those mechanisms. This explicit instruction is important because research by multiple groups has demonstrated that students who are able to break down the relevant mechanisms into smaller steps are up to 10 times more likely to be able to correctly predict the major products for intramolecular reactions.14,35 The ability to decompose mechanisms, therefore, allows students to reason mechanistically.
Corresponding Author
*E-mail:
[email protected]. ORCID
Gautam Bhattacharyya: 0000-0001-9079-5107 Notes
Part of the work described herein was presented at the Awards Symposium in honor of Dr. George M. Bodner at the 255th ACS National Meeting, New Orleans, LA, March 18−22, 2018. The author declares no competing financial interest. 1296
DOI: 10.1021/acs.jchemed.8b00579 J. Chem. Educ. 2019, 96, 1294−1297
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Commentary
(24) Sinclair, J. Corpus, Concordance, Collocation; Oxford University Press: Oxford, U.K., 1991. (25) Ellis, N. C., Ed.; Implicit and Explicit Learning of Languages; Academic Press: London, 1994. (26) Tomasello, M. The item-based nature of children’s early syntactic development. Trends Cognit. Sci. 2000, 4, 156−163. (27) Skehan, P. A Cognitive Approach to Language Learning; Oxford University Press: Oxford, U.K., 1998. (28) Klein, D. Organic Organic Chemistry, 2nd ed.; John Wiley & Sons: Hoboken, NJ, 2014. (29) Bhattacharyya, G.; Harris, M. Compromised structures: Verbal descriptions of mechanism diagrams. J. Chem. Educ. 2018, 95, 366− 375. (30) Skagen, D.; McCollum, B.; Morsch, L.; Shokoples, B. Developing communication confidence and professional identity in chemistry through international online collaborative learning. Chem. Educ. Res. Pract. 2018, 19, 567−582. (31) Bruner, J. The narrative construction of reality. Critical Inquiry 1991, 18, 1−21. (32) Vygostsky, L. Thought and Language, revised ed.; MIT Press: Cambridge, MA, 1997. (33) von Glasersfeld, E. Radical constructivism and teaching. Perspectives 2001, 31, 191−204. (34) Talanquer, V. Concept inventories: Predicting the wrong answer may boost performance. J. Chem. Educ. 2017, 94, 1805−1810. (35) Grove, N.; Cooper, M.; Cox, E. Does mechanistic thinking improve student success in organic chemistry? J. Chem. Educ. 2012, 89, 850−853.
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DOI: 10.1021/acs.jchemed.8b00579 J. Chem. Educ. 2019, 96, 1294−1297
