Research: Science and Education
Teaching a Modified Hendrickson, Cram, and Hammond Curriculum in Organic Chemistry Curriculum Redesign To Turn Around Student Performance Joel M. Karty* and Gene Gooch Department of Chemistry, Elon University, Elon, NC 27244; *
[email protected] B. Gray Bowman Department of Chemistry, High Point University, High Point, NC 27262
Organic chemistry is a notorious course among undergraduates. Its perceived difficulty seems to resonate across all majors. Such infamy, in and of itself, tends not to be so bothersome to organic chemistry professors as much as is the reason for the perceived difficulty. Most students believe that organic chemistry involves an overwhelming amount of memorization, and with each passing year this preconception is perhaps being generated earlier and earlier in a student’s career. Recently, in fact, a student mentioned that her high school chemistry teacher admonished her to “make flash cards every day when you get to organic!” Many of us as professors, on the other hand, believe that such a preconception is in fact a misconception—that success in undergraduate organic chemistry depends predominantly on students’ understanding of basic concepts and basic mechanisms (1–3). Certainly, this is reinforced in undergraduate organic chemistry textbooks, which spend considerable efforts explaining concepts and illustrating mechanisms. Likewise, at Elon University we have always taken great care to echo in class the importance of concepts and mechanisms. Despite what we perceived to be our best efforts, we continued to have difficulty reaching students with regard to the mechanism. By and large, even at the end of the second semester all but about the top 10% of students were incapable of rationalizing straightforward mechanisms. Class morale was low throughout the year, and as a result, the student attrition rate was quite high (at around 50%) and teaching evaluations were below the university average. Moreover, students were not performing well on the ACS standardized final exam. The class average was typically around the 40th percentile, and scores in the 90th percentile were essentially nonexistent. Only two students in Elon’s history had scored at or above the 90th percentile, and those scores were 90th and 96th percentile. These results on the ACS exam were disconcerting for three reasons. First, Elon is a private liberal arts school with relatively small class sizes (about 20–30 per section). Students therefore receive substantial personal attention. Second, the students as a whole bring some talent to the table—their average SAT score is roughly 1150. Third, because of the attrition rate, those exam scores reflect only about the top 50% of students who enter the course in the fall. Not happy with the above indicators, we decided to overhaul our organic chemistry curriculum in order to be more deliberate with concepts and mechanisms. Prior to the 2004– 2005 academic year, organization of material paralleled that in our textbook, Solomons and Fryhle (7th ed.) (4). Like most textbooks on the market, Solomons organizes reactions by the www.JCE.DivCHED.org
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functional group involved, and introduces many fundamental concepts in the context of their application toward reactions. In the fall of 2004, we implemented what might best be described as a modified Hendrickson, Cram, and Hammond (HCH) (5) approach, where reactions are organized by mechanistic type. This new approach incorporated two major modifications from that by HCH: (i) An in-depth introduction to mechanisms—both single step and multistep—before the introduction of reactions; and (ii) an increased focus on fundamental concepts of reactivity prior to the formal introduction of mechanisms. This modified HCH curriculum is described in greater detail below. A remarkable turnaround had occurred in the 2004– 2005 academic year. Positive changes were observed in students’ proficiency with mechanisms, class morale, attrition rate, teaching evaluations and ACS final exam scores. Possible reasons for these outcomes are explored. Modified Hendrickson, Cram, and Hammond Approach Hendrickson, Cram, and Hammond introduced a mechanistic textbook that went into its third edition in 1970. That book was unique in its organization of reactions— reactions were collected in each chapter according to their mechanism rather than the functional group involved in the reaction. Unfortunately, this approach enjoyed limited success. The general opinion of professors at the time was that the students found the HCH approach more difficult to learn from than a functional group approach (6). To make students more receptive to learning reactions by mechanism type, we incorporated two major modifications to the HCH approach. First, we added a unit on mechanisms prior to the formal introduction of reactions. In this unit we focused on how and why a given elementary step would occur, along with its implications on regiochemistry and stereochemistry. We also put considerable focus on understanding and applying rules of thumb for multistep mechanisms. After this presentation of mechanisms, reactions were introduced in an order slightly different from HCH, as follows: 1. Nucleophilic substitution and elimination 2. Nucleophilic addition to polar bonds (such as C⫽O, C⫽N, and C⬅N) 3. Nucleophilic substitution–elimination at polar bonds 4. Electrophilic addition to nonpolar bonds 5. Electrophilic aromatic substitution 6. Diels–Alder and other pericyclic reactions 7. Radical reactions
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The second major modification to the HCH approach was a greater focus on fundamental concepts of reactivity prior to the unit on mechanisms mentioned above. Over the years, we noticed that students tended to avoid mechanisms (and therefore resorted to memorization) in large part because they did not have the proper foundation by the time they were beginning to be held accountable for predicting products. To strengthen that foundation, the following concepts were treated in full, one at a time: 1. Bonding and Lewis structures 2. VSEPR theory and MO theory 3. Isomerism 4. Thermodynamics and chemical kinetics 5. Charge stability 6. Intermolecular forces
Treatment of these concepts in class essentially followed that outlined in Karty’s The Nuts and Bolts of Organic Chemistry: A Student’s Guide to Success (7) (note that the author of that book is also an author of this article). None of these concepts was presented in vacuo; instead, they were introduced in conjunction with several of their applications. For example, in the context of thermodynamics and kinetics, students were exposed not only to pKa, but also to the concept of kinetic and thermodynamic enolates. Additionally, in the context of intermolecular forces, students examined not only physical properties, but also solvent effects on reactions. As another example, students learned to apply charge stability toward a variety of scenarios, including: (i) acidity–basicity; (ii) nucleophilicity; and (iii) the SN1–E1 rate determining step. In this manner, students could clearly see the importance and ubiquity of each fundamental concept, and could also see the close relationship between aspects of organic chemistry that otherwise could seem quite disparate. Two other concepts were introduced prior to mechanisms: nomenclature and spectroscopy. Because nomenclature and spectroscopy do not directly contribute to the story of chemical reactivity and reactions, they were treated in isolation and in their entirety. All of nomenclature was taught in three lecture periods, including the Cahn–Ingold–Prelog rules for stereochemistry. All of spectroscopy, including UV–vis, IR, NMR, and MS was taught in five lecture periods. Certainly, both nomenclature and spectroscopy are integral parts of an organic chemistry course; consequently, their importance was reinforced throughout the entire year by incorporating them into homework, quiz, and exam problems.
We should point out that treatment of nomenclature and spectroscopy in this manner is similar to that presented in HCH. It is also reminiscent of the treatment in textbooks by Allinger and colleagues (8) and by Roberts and Caserio (9). In our modified HCH approach, we used two books throughout the year: Karty’s The Nuts and Bolts of Organic Chemistry (7) and Solomons Organic Chemistry (4). The former was used as the main text in the first semester, and the latter was used to fill in the gaps. In the second semester, Solomons’s book was the only one available to students. This modified HCH approach represented substantial “jumping around” in Solomons’s book in both semesters. Therefore, to help avoid confusion, we provided students a “conversion table” in each semester’s syllabus. Using the table, students could go to the specific pages in Solomons’s book relating to the lecture topic at hand. Assessment Measures and Results
Competence with Mechanisms Students’ ability to work comfortably with mechanisms was assessed largely by their performance on mechanistic questions on in-class exams. Such questions included those that ask for detailed mechanisms of reactions—both reactions that we had examined in detail in class and those that students had not before encountered. Assessment was also done through conversations between students and instructors specifically concerning the role that memorization played in students’ learning of organic chemistry. Class Morale Factors considered in the assessment of class morale include instructor conversations with individual students as well as observations regarding the liveliness and participation of students in class. Furthermore, student evaluations of teaching (SETs), which are discussed below, are taken as a reflection of class morale.
Student Performance Assessment of student performance relies most heavily on the ACS standardized final exam. Table 1 contains both the raw scores and percentile averages of the whole class over a four-year period. However, these numbers are obfuscated by the different attrition rates from one year to the next. Although conclusions can be drawn from such class averages, it is perhaps more insightful to examine average performances
Table 1. Distribution of Elon Student Performance on the ACS Exam at the End of Organic Chemistr y II Academic Year
ACS Exam Version
National
Elon
2001–02
1998
38.7
36.5
45th
2002–03
1998
38.7
34.7
2003–04
2004
39.2
2004–05
1998
38.7
1210
Mean Raw Score
Enrollment for Organic I (N)
Completed Organic II (N)
Student Retention, %
Biology Major Avg. SAT Score
45th
57
30
53
N/A
39th
39th
51
27
53
N/A
35.4
41st
49th
55
40
73
1158
39.3
55th
70th
59
41
69
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Elon Mean Percentile Entire Class Top 53%
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from comparable groups of students from one year to the next. For example, we make comparisons among the average performances of the top 53% of students who enrolled in firstsemester organic chemistry (Table 1). We chose 53% as the number because the attrition rate in academic years 2001– 2002 and 2002–2003 was 47%. Therefore, for the 2001–2002 and 2002–2003 academic years, the top 53% includes scores of all students who took the ACS exam (30 and 27, respectively). In academic year 2003–2004, however, that includes only the top 29 scores out of 40, and in academic year 2004– 2005, that includes only the top 30 students out of 41.
Student Evaluation of Teaching Each year Elon University requires SETs of all courses taught in the fall semester only; teaching evaluation results are therefore available only for first-semester organic chemistry and not for the second semester. The Organic Chemistry SET comprises 10 questions (Table 2), each answered with a number 1–5, where 5 is “strongly agree” and 1 is “strongly disagree”. The 10 questions are provided in Table 2, as are the results from each of the three years one of the authors (JMK) taught first-semester organic chemistry: 2001–2002, 2002–2003, and 2004–2005. For comparison, the departmental averages and the university averages are also provided.
Retention of Material In 2004 we also decided to begin to examine student retention of material. This evaluation was done two ways using the ACS standardized exam. Qualitatively, one can argue that a student’s performance on the ACS exam at the end of the second semester of organic chemistry is in large part a reflection of his or her retention of material throughout the year—students who retain information longer should in general perform better on that exam. This can be said for two reasons: (i) The ACS exam is cumulative over the entire year; and (ii) students in general have little time to study for it (in Elon University’s case, the “reading period” between the end of classes and the beginning of final exams is only one day). As a more quantitative measure of retention of material, students at Elon were asked to take a second ACS organic exam upon their return from summer break. Fifteen volunteers were asked from the pool of students who had completed secondsemester organic chemistry the previous spring, and they were given only 1–2 weeks prior warning. They were specifically asked not to study (surprisingly, no resistance was demonstrated on the part of the students). These students were administered the 2002 version of the ACS exam in the fall, and their percentile scores were compared to those from the 1998
Table 2. Distribution of Elon Student Evaluation of Teaching Results over Time, by Evaluation Statement Statements for Student Response
2001–2002 Averagesa b
2002–2003 Averagesa
Dept.c
Univ.d
4.31
4.71
4.34
4.33
4.24
4.25
4.73
4.43
4.31
3.55
3.97
4.09
4.36
4.04
4.12
4.70
4.57
4.55
4.69
4.87
4.69
4.71
4.30
4.28
3.72
4.23
4.27
4.50
4.25
4.31
4.08
3.91
3.98
3.50
3.76
4.00
4.39
3.92
4.07
7. The instructor provides opportunities for student contact out of class.
4.38
4.16
4.25
3.24
3.90
4.23
4.59
4.15
4.27
8. The instructor expresses concern about student progress in the course.
4.00
4.03
3.96
3.31
3.74
3.93
4.41
3.91
3.99
9. The instructor provides useful feedback on exams and assignments.
3.92
4.00
4.01
3.72
3.78
3.97
4.52
3.96
4.05
4.08
4.08
4.05
3.86
4.02
4.03
4.62
4.08
4.09
4.17
4.19
4.19
3.81
4.04
4.18
4.57
4.18
4.23
Dept.
1. The instructor has clear learning objectives for the course.
4.23
2. The instructor’s class is well prepared and well organized.
d
b
c
2004–2005 Averagesa Organicb
Organic
c
Univ.
Organic
Dept.
4.34
4.31
4.24
4.24
4.23
4.36
4.27
4.43
3. The instructor communicates course material clearly.
3.85
4.05
4.09
4. The instructor displays interest in the subject.
4.69
4.68
5. The instructor summarizes or emphasizes important points in class.
4.23
6. The instructor stimulates my thinking about the subject.
10. The instructor clearly indicates how my work will be evaluated. Totals
Univ.
d
a
Averages are from students’ responses on a Likert-type scale of 1–5 where 5 indicates “strongly agree” and 1 indicates “strongly disagree”. These averages are from students in fall-semester organic chemistry courses only. c These averages are from students in all courses the Chemistry Department offers in the fall semester. d These averages are from students in all courses offered at Elon University in the fall semester. b
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version of the exam taken by the whole class the previous spring. The student performance results from that second test are shown in Table 3. Figure 1 is a plot of Elon students’ percentiles on the 2002 exam relative to the 1998 exam. To provide a context to these numbers, the same study was done at High Point University in High Point, NC, which
is roughly 30 miles from Elon’s campus. That is, the 1998 version of the exam was administered to students there at the end of their second-semester organic chemistry course in the spring of the 2004–2005 academic year, and the 2002 version of the exam was administered to 18 students upon their return in the fall. Results are shown in Table 4 and Figure 2.
Figure 1. Plot of ACS test results comparing Elon student performance on the ACS 2002 final exam (taken after summer break following students’ first year of organic chemistry) plotted against Elon student performance on the ACS 1998 final exam (taken following students’ second-semester organic chemistry course).
Figure 2. Plot of ACS test results comparing High Point student performance on the ACS 2002 final exam (taken after summer break following students’ first year of organic chemistry) plotted against High Point student performance on the ACS 1998 final exam (taken following students’ second-semester organic chemistry course).
Table 4. Distribution of High Point Student Performance on the ACS Exam Following Summer Break Raw Score 1998 ACS Exam
2002 ACS Exam
1998 ACS Exam
2002 ACS Exam
1.
37
23
47
5
2.
35
25
40
7
3.
34
24
36
5
Table 3. Distribution of Elon Student Performance on the ACS Exam Following Summer Break Raw Score 1998 ACS Exam
2002 ACS Exam
Percentile 1998 ACS Exam
2002 ACS Exam
Percentile
1.
62
58
98
88
4.
33
24
33
5
2.
59
43
96
49
5.
28
26
17
8
3.
58
54
96
79
6.
28
23
17
5
4.
54
40
91
41.
7.
28
19
17
2
5.
53
41
90
44
8.
27
27
14
9
6.
50
35
85
27
9.
27
18
14
1
7.
47
32
77
20
10.
26
22
11
4
8.
45
34
72
25
11.
25
22
9
4
9.
42
40
63
41
12.
25
18
9
1
10.
38
37
51
33
13.
25
18
9
1
11.
38
33
51
22
14.
23
14
5
0
12.
36
34
43
25
15.
21
24
2
5
13.
35
30
40
15
16.
21
23
2
5
14.
30
22
22
4
17.
21
14
2
0
15.
30
31
22
17
18.
19
18
1
1
45.2
37.6
66.5
35.3
26.8
21.2
Avg.
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Avg.
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15.8
3.8
Research: Science and Education
High Point University was chosen because it is a fouryear institution that is comparable to Elon in terms of student demographics, and the organic chemistry curriculum is taught using the traditional approach of organizing the material by functional group. By and large, the course follows the curriculum outlined in Ege’s textbook (10), and mechanisms are highly emphasized in class. We note that these comparisons using all scores may not be appropriate because the average percentiles on the 1998 exam are not very similar between the two schools (66.5 percentile for Elon and 15.8 percentile from High Point). In part this is because a number of the better-performing High Point University organic chemistry students were seniors and had already graduated. We can, however, make direct comparisons using only the subset of students whose raw scores ranged between 30 and 40 (22nd and 57th percentile) on the 1998 version of the exam. This includes six students from Elon and four students from High Point (Table 5).
Table 5. Comparison between Elon Students and High Point Students on the ACS Exam Following Summer Break Elon Students’ Percentiles 1998 ACS Exam
2002 ACS Exam
High Point Students’ Percentiles 1998 ACS Exam
2002 ACS Exam
1.
51
33
47
5
2.
51
22
40
7
3.
43
25
36
5
4.
40
15
33
5
5.
22
17
6.
22
39.0
5.5
Avg.
4
38.2
19.3
Discussion
Student Performance
Competence with Mechanisms Students were much more competent with mechanisms under the new curriculum than under that in which material was organized by functional group. First and foremost, students were not relying on memorization to succeed. In fact, on multiple occasions throughout the year students asked “What do students normally memorize?” Furthermore, students went so far as to claim that by comparison, general chemistry involves a tremendous amount of memorization. Students’ competence with mechanisms was also demonstrated on their in-class exams. In previous years, most students would struggle tremendously with questions that asked for the detailed mechanism of a given reaction—even those reactions we focused on in class, such as the Fischer esterification. On one of the exams in 2004 (following the curriculum redesign), however, students were asked to provide the detailed mechanism for the hydrolysis of an imine—one whose mechanism is related to a Fischer esterification, but one that they had not seen before. The majority of students (roughly three-fourths) successfully drew that mechanism. In previous years, we would not have considered including a mechanism question like that on an exam.
In 2004–2005 the class average on the ACS final exam was the highest in Elon’s history. Whereas the average percentile typically has hovered around the 40th percentile, students averaged 55th percentile (see Table 1). More impressive, perhaps, is the fact that five students scored at or above the 90th percentile: 90th, 91st, 96th, 96th, and 98th percentiles, respectively. Recall that previously, only two students in Elon’s history had done so, scoring at the 90th and 96th percentile. Perhaps more telling is the comparison of the scores from the top 53% of students initially enrolled in first-semester organic chemistry. In 2004–2005, this translated into the top 30 ACS exam scores, for which the average was the 70th percentile. In previous years, similar groups of students averaged between the 39th and 49th percentile. Are these increases in the ACS exam scores caused by differences among the groups of students rather than the redesigned curriculum? Average SAT scores (Table 1) are one proxy measure for comparing students. Elon University has been keeping track of average first-year SAT scores by major since the 2002–2003 academic year. Of greatest relevance to organic chemistry is the average SAT score of entering biology majors, because they comprise roughly 80% of the class. For the 2003–2004 organic chemistry class, the average biology SAT score was 1158 (entering class 2002–2003), whereas that for the 2004–2005 organic chemistry class was 1149 (entering class 2003–2004). This strongly suggests that the better student performances on the ACS exam are not related to any underlying differences among the students.
Class Morale Since we implemented the redesigned curriculum, we have noticed that class morale has been consistently high throughout the entire year. Unlike previous years, there was never a point where the class as a whole felt defeated. On the contrary, discussions in class are much livelier than before and students remain attentive and eager to learn. To an extent, the morale of the class is also reflected in the superb teaching evaluations, which are significantly improved over previous years. Much of the higher morale probably has to do with the fact that students felt they had command of the course material, rather than the material having control over them. Furthermore, there is of course a synergistic relationship between morale and student performance—students are performing better on the in-class exams, which bolsters their self-esteem, and vice versa. www.JCE.DivCHED.org
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Student Evaluation of Teaching The SET results specific to first-semester organic chemistry are shown in Table 2. In all 10 categories, the scores that JMK received were not only the highest in his career, but were also significantly higher than both the departmental average and the university average. Student responses to questions 1–3 showed substantial improvements from years past. These ask students to rate the clarity of learning objectives, how well the course is prepared and organized, and how clearly the instructor communicates.
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Improvements on these questions could be a direct outcome of the organization of material by concept and mechanism as opposed to functional group; students could better see organic chemistry unfolding as a coherent story. Somewhat surprising are the large increases for questions 9 and 10, which are both about 0.6 points higher than in previous years. These questions ask students about feedback on exams and assignments and about the clarity with which student work is evaluated. The reason that these results are somewhat surprising is that JMK believes that no effort was spent to improve the way in which student work was evaluated and feedback to students was provided. Therefore, once again, this could be an outcome of the organization of material by concept and mechanism. If students had a clearer understanding of the material, then with the same feedback and evaluation as in years past they very well could have been better equipped to make adjustments. Another SET question that deserves mention is question 7, which asks students about opportunities for contact with the instructor outside of class. The score JMK received on this question was about 0.2 points higher than in previous years. However, in 2004–2005 JMK believes he was in fact less available than he had been in the past, largely because of increased pressures of research and scholarship. Instead, students probably perceived him as being more available, perhaps because they had better command of the material and therefore required less time with the instructor.
Retention of Material As mentioned earlier, the scores students earn on the ACS final exam is in part a reflection of their long-term retention of material—the ACS exam is cumulative over the entire year and students have relatively little time to prepare for it. Given that students in 2004–2005 as a whole scored better than any class in Elon’s history (see Table 1), it can be argued that students in general were better able to retain the material they had learned. Significantly more insight is provided by the second ACS exam students were asked to take in the fall semester following the summer after completing their year of organic chemistry. Not surprisingly, the percentile score each student received on the second ACS exam was lower than they received on the first exam, and that fall-off varied significantly from one student to the next. On average, however, the percentile score each Elon student received on the second exam was 53% of the percentile score they received on their first exam (Figure 1). Quite impressive were two of the top-performing students, who demonstrated substantial retention of material over the summer. A student who scored 98th percentile on the first exam scored 88th percentile on the second exam, and a student who scored 96th percentile on the first exam scored 79th percentile on the second exam. Additional meaning is given to these numbers by comparing students from Elon University to those from High Point University in Figures 1 and 2. These two plots have a strikingly different slope. Whereas in Figure 1 (Elon) there is a significantly positive correlation (slope ∼0.65) between the percentiles from the 2002 exam and percentiles from the 1998 exam, Figure 2 (High Point) shows that the percentiles from
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the 2002 exam are relatively independent of the percentiles from the 1998 exam (slope ∼0.09). Therefore, whereas the Elon students’ percentiles on the 2002 exam were highly dependent upon their percentiles from the 1998 exam, all High Point students had very similar percentiles on the 2002 exam. Moreover, the average fall-off of the percentiles was quite different between the two schools. The average percentile of the 15 Elon participants fell from about 66.5 percentile on the 1998 exam to 35.3 percentile on the 2002 exam. That is, on average, Elon students’ percentiles on the 2002 exam were about 53% of their percentiles on the 1998 exam. On the other hand, the 18 High Point students’ percentiles on average fell from about 15.8 percentile to about 3.8 percentile, or to about 24% of their original percentiles. As alluded to previously, however, it may not be appropriate to compare all scores from the two schools, given that the average percentiles on the 1998 exam were significantly different (66.5 percentile for Elon students and 15.8 percentile for High Point students). We can, however, make more direct comparisons among subgroups of students whose raw scores were between 30 and 40 on the 1998 exam (Table 5), which includes six Elon students and four High Point students. For both groups of students, the average 1998 exam percentiles were about the same—38.2 percentile for the six Elon students and 39.0 percentile for the four High Point students. On the 2002 exam, however, the average percentiles of these two groups of students were quite different—the Elon students scored an average of about 19.3 percentile, whereas the High Point students scored an average of about 5.5 percentile. In other words, the Elon students’ average percentile on the 2002 exam was about 50.5% of their average percentile on the 1998 exam. On the other hand, the High Point students’ average percentile on the 2002 exam was only about 14.1% of their average percentile on the 1998 exam. It therefore appears that those Elon students had significantly longer retention of their organic chemistry knowledge over the summer than did the High Point students. Governing Factors In the 2004–2005 academic year, we made substantial changes to the organic chemistry curriculum at Elon to teach the material in a much more linear way with respect to fundamental concepts, mechanisms, and reactions. During that academic year we observed a remarkable turnaround from previous years. Students’ ability to work comfortably with mechanisms vastly improved. Class morale was consistently much higher throughout the year, and teaching evaluations were significantly better. Moreover, the class performance on the ACS final exam was much better than any class in Elon’s history, and students’ retention of knowledge (as tested following summer break) was remarkable. In summary, students were learning and understanding the material as opposed to memorizing. Why? Specifically what were the factors that caused such a turnaround? Although the answer to this question is far from clear, one possibility could be that the instructor (JMK) was simply more enthusiastic in his teaching under the new curriculum, and this enthusiasm was contagious. It is difficult to argue
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against this, but we do not believe that this is the case. In fact, some support of our belief is provided by question 4 in the student evaluations of teaching, which asks the students to consider the statement: “The instructor displays interest in the subject.” Even in the years prior to invoking the new curriculum, JMK scored quite highly on this question—ranging from about 4.6–4.7 out of a maximum of 5. Granted, in the 2004–2005 academic year, Karty’s score on this question did rise to above 4.8. We would like to suggest instead that a major factor was the organization of the material itself. In other words, organization of the material linearly with respect to concepts and reactivity provides a number of advantages as compared to organization of the material by functional group. As described below, those advantages include: (i) Providing a natural tie between reactions; (ii) Providing fewer distractions; and (iii) Removing the temptation to memorize.
A Natural Tie between Reactions Although functional groups provide a clean way in which to organize reactions, they are not the natural tie between reactions—mechanisms are. A given functional group may undergo widely different reactions simply by changing the reaction conditions. One example involves ketones and aldehydes. The carbonyl group can act as an electrophile, undergoing attack by a nucleophile under one set of conditions. Under another set of conditions, the ketone becomes a nucleophile itself. Perhaps a better example is with alkyl halides, which can undergo four different reactions—SN1, SN2, E1, and E2—depending upon the specific reaction conditions. As a result, instead of promoting a mechanistic understanding of reactions, organization by functional group tends to promote the notion of functional group transformations, which may inherently lend itself to memorization. Our modified HCH approach, however, may allow students to better see the simplicity of organic chemistry. Reactions are governed by just a handful of basic mechanisms, and are modulated by differences in characteristics of reactants and by reaction conditions. Moreover, such organization allows students to better see the close connection between reactions that otherwise might seem unrelated. For example, students see that each of the following reactions are simply variations of the SN2 reaction: conversion of an alcohol to a bromide using PBr3; halogenation of alpha carbons; alkylation of alpha carbons; alkylation of amines; and formation of a Wittig reagent. In a typical textbook organized by functional group, on the other hand, these reactions are found in multiple different chapters, thereby de-emphasizing the centrality of the mechanism. Fewer Distractions Typically, a functional group chapter contains a variety of independent pieces of information—nomenclature rules, physical properties, spectroscopic information, compound preparations, new reactions, new mechanisms to explain those reactions, and new concepts to explain those mechanisms. From a student’s perspective, this must seem quite overwhelming. If students face this in each chapter, how can we expect them to focus on understanding the concepts and
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mechanisms at hand? Moreover, how can we expect them to carry that understanding forward to each successive chapter? The approach that we have presented here enables students to focus on a single concept or mechanism at a time, free from distractions. Furthermore, concepts that are not central to chemical reactivity—i.e., nomenclature and spectroscopy—are presented separately and in their entirety. Therefore, students can perhaps better see what is part of the coherent story of reactivity and reactions than they otherwise could under a functional group organization.
Removing the Temptation To Memorize As mentioned above, even before students begin organic chemistry they tend to have a preconception that the course is predominantly memorization. Specifically, they tend to believe that countless reactions constitute the bulk of that memorization. Therefore, it should not be surprising that if a student is presented with concepts, mechanisms, and reactions all together early in the course, they tend to gravitate toward the reactions alone. In other words, students tend not to use concepts and mechanisms to understand reactions, but rather commit to memory just the reactants, reagents, and products. The approach that we have described here may remove the temptation to memorize by delaying the formal introduction of reactions until much later in the course. By the time students begin to see reactions (and, more to the point, are held accountable for predicting products), they will have developed a much stronger foundation of concepts and mechanisms than they would under our previous functional group organization. Therefore, students are perhaps much more receptive to actually employing concepts and mechanisms toward understanding reactions (and predicting products). Future Directions What is presented here is essentially the story of a turnaround of one school’s organic chemistry program. Based on the outcome of implementing a new curriculum, we propose that there may be substantial advantages to organizing organic chemistry by concept, mechanism, and reaction type, as opposed to a more traditional organization by functional group. However, at present this is simply a hypothesis. Certainly there are numerous instructors who have enjoyed quite a bit of success under a functional group organization. Indeed, under a functional group organization, emphasizing concepts and mechanisms can be quite effective. Our future plans therefore include carrying out a formal chemical education research project to provide insight into the importance of the organization of material. Several researchers from a variety of schools will be involved—both instructors who feel they have had success under a functional group organization and those who feel they have not. Each will implement the modified HCH approach we have described, and indicators such as ACS exam scores, teaching evaluations, and long-term student retention of the material will be compared both before and after implementation of the new curriculum. Student interviews will also be conducted. Until then, the results we have presented here may be viewed as preliminary results for future chemical education research.
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Conclusion
Literature Cited
In the 2004–2005 academic year, a modified HCH curriculum was introduced in our organic chemistry course, focusing on fundamental concepts, mechanisms, and reactions in a highly linear fashion. After implementation of this new curriculum, significantly positive impacts were seen regarding:
1. Pungente, M. D.; Badger, R. A. J. Chem. Educ. 2003, 80, 779– 784. 2. Taagepera, M.; Noori, S. J. Chem. Educ. 2000, 77, 1224– 1229. 3. Scudder, P. H. J. Chem. Educ. 1997, 74, 777–781. 4. Solomons, G.; Fryhle, C. Organic Chemistry, 7th ed.; John Wiley & Sons: New York, 2000. 5. Hendrickson, J. B.; Cram, D. J.; Hammond, G. S. Organic Chemistry, 3rd ed.; McGraw-Hill Book Company: New York, 1970. 6. John Brauman, Stanford University Department of Chemistry, personal communication, 2006. 7. Karty, J. The Nuts and Bolts of Organic Chemistry: A Student’s Guide to Success, 1st ed.; Benjamin Cummings: San Francisco, 2006. 8. Allinger, N. L.; Cava, M. P.; DeJongh, D. C.; Johnson, C. R.; Lebel, N. A.; Stevens, C. L. Organic Chemistry, 2nd ed.; Worth: New York, 1976. 9. Roberts, J. D.; Caserio, M. C. Basic Principles of Organic Chemistry, 2nd ed.; Addison Wesley: New York, 1977. 10. Ege, S. N. Organic Chemistry: Structure and Reactivity, 5th ed.; Houghton Mifflin Co.: Boston, 2004.
1. Students’ competence with mechanisms 2. Class morale 3. Student performance on the ACS exam 4. Student evaluations of teaching 5. Students’ long-term retention of material
We propose that these outcomes may be a direct result of the organization of the material itself, with the presentation of topics in the redesigned course providing significant advantages over a more traditional functional group organization. Further research involving other schools and other instructors is required to lend support to such a hypothesis. Acknowledgments We thank the reviewers for their insightful comments, which helped to make this a stronger paper.
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