a research-based laboratory course in organic chemistry - supporting information

7/25/2019 A Research-Based Laboratory Course in Organic Chemistry - Supporting Information

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Chemistry 252/254 Survey

At the beginning of the year you received a handout that described the objectives of

this course. Those objectives are itemized below. Please indicate your assessment of

whether we achieved those goals or not by circling the appropriate number next to each

goal.

1 means very satisfactory, 3 means satisfactory, 5 means very unsatisfactory.

I Did you:

1. gain an appreciation of the way chemists do chemistry, 1 2 3 4 5

2. including the generation of data, 1 2 3 4 5

3.

collection of data, 1 2 3 4 5

4.

interpretation of data, 1 2 3 4 5

5. presentation of experimental results, 1 2 3 4 5

6. learn how to keep an accurate notebook? 1 2 3 4 5

7.

increase your ability to use the chemical literature? 1 2 3 4 5

8.

developed competence in:

A. the design and execution of a synthetic reaction? 1 2 3 4 5

B. thin layer chromatography? 1 2 3 4 5

C.

crystallization and recrystallization? 1 2 3 4 5

D. handling air and moisture sensitive materials? 1 2 3 4 5

E. 1H and 13C NMR spectroscopy and IR spectroscopy? 1 2 3 4 5

1. learn how to use several molecular modeling programs? 1 2 3 4 5



IIA. Compared to your introductory chemistry laboratory courses, how would you rate

your experience in this course?

1. Excellent 2. Superior 3. About the Same 4. Inferior 5. Very Poor

B. Please assess your level of understanding and mastery of the following techniques on

a scale from 1 to 5 where 1 means that your are very satisfied with your ability to

perform the technique and 5 means that you are very dissatisfied. Circle your answer.

(a.) mp/bp determination determination 1 2 3 4 5

(b.) tlc 1 2 3 4 5

(c.) column chromatography 1 2 3 4 5

(d.) recrystallization 1 2 3 4 5

(e.) IR spectroscopy 1 2 3 4 5

(f.) H-NMR spectroscopy 1 2 3 4 5

(g.) C-NMR spectroscopy 1 2 3 4 5

(h.) Inert atmosphere transfers 1 2 3 4 5

C. Would you comment on the importance of having a multinuclear (hydrogen andcarbon) NMR that is easy for students to run for this course? (The instrument would

operate with an interface similar to the IR spectrometer.) Please feel free to include a

separate page with your comments on questions C & D.

D. If you feel that you can comment on the advantages/disadvantages of having a

research-based organic laboratory curriculum vs. the more traditional "cookbook"

style, please do. If possible, would you describe the specific cookbook-style

laboratories (title of course &/or USM department and number) that you are using as

a basis for your comments in the first part of this question.



Chemistry 252 and 254 Survey Results

September 2003

David L. Silvernail Paula B. Gravelle

University of Southern Maine University of Southern Maine

Analysts from the Center for Education Policy, Applied Research, and Evaluation

(CEPARE) were asked to analyze the surveys of students from the Chemistry 252 and

254 classes. The survey asked students at the end of six different semesters to respond to

questions relating to their experiences in the class. In Section I the survey asked for an

assessment of whether or not the goals described at the beginning of the course were

achieved on a scale of 1 (Very Satisfactory) to 5 (Very Unsatisfactory). Section II asked

students to rate their overall experience in this course when compared to their

introductory chemistry courses on a scale of 1 (Excellent) to 5 (Very Poor). And finally,Section III asked students to assess their level of understanding and mastery of specific

techniques on a scale of 1 (Very Satisfied with ability to perform the technique) to 5

(Very Dissatisfied).

Figures depicting survey responses are attached to this summary. The major

conclusion we have reached after reviewing the survey data is: while the analysis shows

some variation between semesters throughout, the majority of responses were very

positive with the general trend showing improvement or maintaining very positive

responses over the length of the project . More specifically, with regards to:

Section III: Understanding & Mastery of Techniques

! Of the eight techniques in question, two scored fairly high for all semesters, an

average of 92.5% of respondents were Somewhat to Very Satisfied with their

abilities in mp/bp determination; and 79% were Somewhat to Very Satisfied with

their abilities in tlc.

! Four of the techniques; recrystallization, IR spectroscopy, H-NMR spectroscopy,

and inert atmosphere transfers had an average range throughout all semesters of

between 51.1% and 67.4% who were Somewhat to Very Satisfied with their

abilities; with the majority of the remaining respondents being Neutral in their

assessment.



! The final two techniques, column chromatography and C-NMR spectroscopy, had

a significantly lower percentage of responses in the Somewhat to Very Satisfied

category within 3 of the 6 semesters. However, even in these cases, assessments

were more Neutral than Dissatisfied.

Section I: Course Objectives Obtained

! Overall the percentage of students whose responses were Satisfactory to Very

Satisfactory in each of the 13 course objectives was very high. For 5 of the

objectives, between 91% and 94% of the students gave ratings of Satisfied to

Very Satisfied; and for 7 of the objectives between 86% and 89% of students said

they were Satisfied to Very Satisfied.

! The final objective, learning to use several molecular modeling programs, had a

significantly lower, but still very positive overall rating of approximately 70%

throughout all semesters being Satisfied to Very Satisfied. One semester in

particular, Spring 2000, had 61.1% of students who were Somewhat to Very

Unsatisfied with this objective.

! One other note, the Spring 2001 semester respondents were 100% Satisfied to

Very Satisfied in all but 3 of the course objectives, those were learning how to use

several molecular modeling programs, how to keep an accurate notebook, and

gaining an appreciation of the way chemists do the presentation of experimentalresults.

Section II Analysis: Overall Lab Experience

!

A majority, (57.4%) of respondents rated their overall experience in this course

Superior to Excellent when compared to their introductory chemistry laboratory

courses.

!

A little over a third, (35.6%) of all students rated this course About the Same as

their introductory courses.




Question 1: Did you gain an appreciation of the way chemists do chemistry?

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 66.7% 16.7% 11.1% 5.6% 0.0%

Fall 2000 18.8% 37.5% 25.0% 12.5% 6.3%

Spring 2001 61.5% 38.5% 0.0% 0.0% 0.0%

Fall 2002 60.0% 20.0% 6.7% 13.3% 0.0%

Spring 2002 36.4% 36.4% 27.3% 0.0% 0.0%

Spring 2003 68.2% 18.2% 9.1% 4.5% 0.0%

Very Satisfactory Substantially

Satisfactory Satisfactory

Somewhat

Unsatisfactory

Very

Unsatisfactory




Question 2: Did you gain an appreciation of the way chemists do the generation of

data?

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 50.00% 27.80% 16.70% 5.60% 0.00%

Fall 2000 25.00% 37.50% 18.80% 18.80% 0.00%

Spring 2001 38.50% 38.50% 23.10% 0.00% 0.00%

Fall 2002 40.00% 33.30% 13.30% 6.70% 6.70%

Spring 2002 18.20% 36.40% 36.40% 9.10% 0.00%

Spring 2003 50.00% 40.90% 4.50% 4.50% 0.00%



Somewhat

Unsatisfactory

Very

Unsatisfactory




Question 3: Did you gain an appreciation of the way chemists do the collection of

data?

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 50.00% 33.30% 11.10% 5.60% 0.00%

Fall 2000 31.30% 25.00% 31.30% 12.50% 0.00%

Spring 2001 53.80% 23.10% 23.10% 0.00% 0.00%

Fall 2002 40.00% 33.30% 20.00% 6.70% 0.00%

Spring 2002 27.30% 27.30% 45.50% 0.00% 0.00%

Spring 2003 54.50% 22.70% 18.20% 4.50% 0.00%



Somewhat

Unsatisfactory

Very

Unsatisfactory




Question 4: Did you gain an appreciation of the way chemists do the interpretation

of data?

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 16.70% 44.40% 33.30% 0.00% 5.60%

Fall 2000 31.30% 25.00% 31.30% 6.30% 6.30%

Spring 2001 30.80% 53.80% 15.40% 0.00% 0.00%

Fall 2002 20.00% 46.70% 26.70% 6.70% 0.00%

Spring 2002 36.40% 0.00% 27.30% 27.30% 9.10%

Spring 2003 31.80% 50.00% 13.60% 4.50% 0.00%



Somewhat

Unsatisfactory

Very

Unsatisfactory




Question 5: Did you gain an appreciation of the way chemists do the presentation of

experimental results?

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 22.20% 38.90% 27.80% 5.60% 5.60%

Fall 2000 6.70% 40.00% 33.30% 13.30% 6.70%

Spring 2001 30.80% 30.80% 23.10% 15.40% 0.00%

Fall 2002 33.30% 46.70% 6.70% 13.30% 0.00%

Spring 2002 18.20% 27.30% 45.50% 9.10% 0.00%

Spring 2003 36.40% 54.50% 4.50% 4.50% 0.00%



Somewhat

Unsatisfactory

Very

Unsatisfactory




Question 6: Did you learn how to keep an accurate notebook?

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 44.40% 33.30% 16.70% 5.60% 0.00%

Fall 2000 43.80% 31.30% 12.50% 12.50% 0.00%

Spring 2001 61.50% 15.40% 15.40% 7.70% 0.00%

Fall 2002 66.70% 20.00% 6.70% 0.00% 6.70%

Spring 2002 45.50% 18.20% 36.40% 0.00% 0.00%

Spring 2003 54.50% 36.40% 4.50% 4.50% 0.00%


Satisfactory

Satisfactory Somewhat

Unsatisfactory

Very

Unsatisfactory




Question 7: Did you increase your ability to use the chemical literature?

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 22.20% 22.20% 33.30% 16.70% 5.60%

Fall 2000 12.50% 43.80% 25.00% 12.50% 6.30%

Spring 2001 15.40% 61.50% 23.10% 0.00% 0.00%

Fall 2002 40.00% 13.30% 33.30% 6.70% 6.70%

Spring 2002 27.30% 27.30% 27.30% 18.20% 0.00%

Spring 2003 13.60% 50.00% 27.30% 4.50% 4.50%

Very Satisfactory SubstantiallySatisfactory

Satisfactory SomewhatUnsatisfactory

VeryUnsatisfactory




Question 8A: Did you develop competence in the design and execution of a synthetic

reaction?

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 17.60% 35.30% 41.20% 5.90% 0.00%

Fall 2000 0.00% 43.80% 37.50% 18.80% 0.00%

Spring 2001 23.10% 46.20% 30.80% 0.00% 0.00%

Fall 2002 26.70% 46.70% 13.30% 6.70% 6.70%

Spring 2002 18.20% 27.30% 27.30% 27.30% 0.00%

Spring 2003 27.30% 50.00% 13.60% 9.10% 0.00%



Somewhat

Unsatisfactory

Very

Unsatisfactory




Question 8B: Did you develop competence in thin layer chromatography?

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 61.10% 16.70% 0.00% 11.10% 11.10%

Fall 2000 31.30% 31.30% 25.00% 6.30% 6.30%

Spring 2001 53.80% 38.50% 7.70% 0.00% 0.00%

Fall 2002 53.30% 13.30% 26.70% 6.70% 0.00%

Spring 2002 9.10% 36.40% 36.40% 18.20% 0.00%

Spring 2003 54.50% 18.20% 13.60% 4.50% 9.10%


Satisfactory Satisfactory Somewhat

Unsatisfactory

Very

Unsatisfactory




Question 8D: Did you develop competence in handling air and moisture sensitive

materials?

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 22.20% 44.40% 16.70% 5.60% 11.10%

Fall 2000 13.30% 26.70% 20.00% 26.70% 13.30%

Spring 2001 46.20% 23.10% 30.80% 0.00% 0.00%

Fall 2002 33.30% 46.70% 13.30% 6.70% 0.00%

Spring 2002 36.40% 36.40% 18.20% 9.10% 0.00%

Spring 2003 50.00% 36.40% 4.50% 9.10% 0.00%



Somewhat

Unsatisfactory

Very

Unsatisfactory




Question 8E: Did you develop competence in 1H and 13CNMR spectroscopy and IR

spectroscopy?

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 16.70% 38.90% 16.70% 16.70% 11.10%

Fall 2000 18.80% 31.30% 31.30% 12.50% 6.30%

Spring 2001 69.20% 23.10% 7.70% 0.00% 0.00%

Fall 2002 46.70% 40.00% 13.30% 0.00% 0.00%

Spring 2002 27.30% 18.20% 36.40% 18.20% 0.00%

Spring 2003 45.50% 27.30% 22.70% 4.50% 0.00%



Somewhat

Unsatisfactory

Very

Unsatisfactory




Question 9: Did you learn how to use several molecular modeling programs?

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 5.60% 22.20% 11.10% 16.70% 44.40%

Fall 2000 6.70% 33.30% 53.30% 0.00% 6.70%

Spring 2001 38.50% 30.80% 23.10% 0.00% 7.70%

Fall 2002 16.70% 16.70% 25.00% 16.70% 25.00%

Spring 2002 9.10% 9.10% 45.50% 18.20% 18.20%

Spring 2003 4.50% 36.40% 31.80% 13.60% 13.60%


Satisfactory Satisfactory Somewhat

Unsatisfactory

Very

Unsatisfactory



Section II: Overall Lab Experience

Question 1: Compared to your introductory chemistry laboratory courses, how

would you rate your experience in this course?

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 18.80% 50.00% 31.30% 0.00% 0.00%

Fall 2000 6.70% 6.70% 73.30% 6.70% 6.70%

Spring 2001 23.10% 38.50% 30.80% 7.70% 0.00%

Fall 2002 23.10% 61.50% 7.70% 7.70% 0.00%

Spring 2002 10.00% 30.00% 40.00% 20.00% 0.00%

Spring 2003 30.00% 40.00% 30.00% 0.00% 0.00%

Excellent Superior About the Same Inferior Very Poor




Question a: Please assess your level of understanding and mastery of the following

techniques: mp/bp determination.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 77.80% 5.60% 11.10% 5.60% 0.00%

Fall 2000 50.00% 37.50% 0.00% 12.50% 0.00%

Spring 2001 100.00% 0.00% 0.00% 0.00% 0.00%

Fall 2002 93.30% 0.00% 0.00% 6.70% 0.00%

Spring 2002 72.70% 18.20% 9.10% 0.00% 0.00%

Spring 2003 85.70% 14.30% 0.00% 0.00% 0.00%

Very Satisfied Somewhat

Satisfied Neutral

Somewhat

Dissatisfied Very Dissatisfied




Question b: Please assess your level of understanding and mastery of the following

techniques: tlc.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 66.70% 27.80% 5.60% 0.00% 0.00%

Fall 2000 37.50% 12.50% 31.30% 18.80% 0.00%

Spring 2001 61.50% 38.50% 0.00% 0.00% 0.00%

Fall 2002 60.00% 20.00% 6.70% 13.30% 0.00%

Spring 2002 18.20% 45.50% 27.30% 9.10% 0.00%

Spring 2003 57.10% 28.60% 14.30% 0.00% 0.00%


Satisfied Neutral

Somewhat





Question c: Please assess your level of understanding and mastery of the following

techniques: column chromatography.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 0.00% 11.80% 41.20% 11.80% 35.30%

Fall 2000 7.10% 7.10% 42.90% 14.30% 28.60%

Spring 2001 38.50% 15.40% 30.80% 7.70% 7.70%

Fall 2002 40.00% 33.30% 20.00% 6.70% 0.00%

Spring 2002 9.10% 0.00% 36.40% 27.30% 27.30%

Spring 2003 28.60% 28.60% 33.30% 9.50% 0.00%


Satisfied Neutral

Somewhat





Question d: Please assess your level of understanding and mastery of the following

techniques: recrystallization.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 5.60% 44.40% 44.40% 0.00% 5.60%

Fall 2000 12.50% 31.30% 50.00% 0.00% 6.30%

Spring 2001 38.50% 15.40% 38.50% 7.70% 0.00%

Fall 2002 46.70% 26.70% 13.30% 13.30% 0.00%

Spring 2002 18.20% 36.40% 36.40% 9.10% 0.00%

Spring 2003 23.80% 33.30% 33.30% 9.50% 0.00%


Satisfied Neutral

Somewhat





Question e: Please assess your level of understanding and mastery of the following

techniques: IR spectroscopy.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 16.70% 61.10% 5.60% 11.10% 5.60%

Fall 2000 12.50% 37.50% 31.30% 12.50% 6.30%

Spring 2001 23.10% 15.40% 46.20% 15.40% 0.00%

Fall 2002 73.30% 20.00% 6.70% 0.00% 0.00%

Spring 2002 27.30% 36.40% 36.40% 0.00% 0.00%

Spring 2003 52.40% 28.60% 14.30% 4.80% 0.00%


Satisfied Neutral

Somewhat





Question f: Please assess your level of understanding and mastery of the following

techniques: H-NMR spectroscopy.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 11.10% 33.30% 33.30% 11.10% 11.10%

Fall 2000 37.50% 6.30% 31.30% 25.00% 0.00%

Spring 2001 61.50% 23.10% 15.40% 0.00% 0.00%

Fall 2002 40.00% 40.00% 6.70% 13.30% 0.00%

Spring 2002 27.30% 18.20% 45.50% 9.10% 0.00%

Spring 2003 23.80% 38.10% 23.80% 4.80% 9.50%


Satisfied Neutral

Somewhat





Question g: Please assess your level of understanding and mastery of the following

techniques: C-NMR spectroscopy.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 0.00% 23.50% 17.60% 23.50% 35.30%

Fall 2000 6.70% 6.70% 40.00% 33.30% 13.30%

Spring 2001 30.80% 23.10% 38.50% 7.70% 0.00%

Fall 2002 26.70% 33.30% 26.70% 13.30% 0.00%

Spring 2002 27.30% 18.20% 27.30% 27.30% 0.00%

Spring 2003 15.00% 35.00% 30.00% 10.00% 10.00%


Satisfied Neutral

Somewhat





Question h: Please assess your level of understanding and mastery of the following

techniques: Inert atmosphere transfers.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Spring 2000 5.90% 29.40% 11.80% 5.90% 47.10%

Fall 2000 13.30% 6.70% 33.30% 13.30% 33.30%

Spring 2001 38.50% 30.80% 30.80% 0.00% 0.00%

Fall 2002 20.00% 40.00% 40.00% 0.00% 0.00%

Spring 2002 27.30% 18.20% 54.50% 0.00% 0.00%

Spring 2003 33.30% 42.90% 14.30% 9.50% 0.00%


Satisfied Neutral

Somewhat




Henry Tracy

Department of ChemistryUniversity of Southern Maine

P.O. Box 9300

Portland, ME 04104

Dear Hank

The following reports discusses the laboratory materials that you generated as part of the

CCLI grant you received in 1999 for the inclusion of organometallic chemistry into the

organic program at USM. The comments bellowed are based on a set of 12 student lab

reports – presumably randomly chosen- that related the specific steps taken in the multi-step sequence. The chemistry presented falls squarely into my area of expertise as a

classically trained organic chemist who explores early transition metal chemistry in the

research lab. Overall, I found the reaction sequence to be the most original and novelmulti week lab programs that I have seen over the last decade and I am impressed withthe level of technical sophistication that is evidenced by the individual students as the

approach the final stages of the scheme.

The overall sequence of reactions accomplishes several important goals for the organicsequence. First, it gave the students an interesting series of reactions to explore that had

obvious relevance within your department’s research program. This set of reactions

reinforced standard lecture reactions such as the dibromination of an alkene and E2elimination reactions in a fashion that showed students that the reactions were not

substrate dependant. Second, it taught important techniques- necessary for the modern

research laboratory- that are often left out of the traditional organic research lab, such assyringe techniques, air-sensitive reagent handling and uniquely, glove box methods.Third, it has the ability to introduce the concepts of a combinatorial approach to substrate

production as the students prepared a variety of diphenylacetylene substrates (I do note,

however, that there is no evidence in the reports that you pursued this intellectual line).

Finally, the use of groups for the work allowed research teams to form and form thereports this appeared to lessen the amount of decision making stress involved as the

students moved through the process.

The set of reactions chosen for this process were well chosen to explore many areas oforganic chemistry. Most of the reactions are “textbook” examples within the organic

curriculum and provide excellent opportunities for student to make easily isolableproducts that can be characterized by the instrumentation that is readily available in most

research labs, including IR and NMR. The Wittig sequence gave a variety of stilbenesthat are readily characterized by NMR and IR. Of the lab reports that I reviewed (two

for stilbene itself and one for 4methoxy 4’CF3 stilbene) each student missed some of the

distinguishing features within the IR or NMR, but their data showed that the data was

there to be correctly interpreted. The same can be said for any of the reports that I readand should not be considered a negative for this sequence. (As I note below, this reaction



sequence is likely to be easier to follow in labs that have high field NMR capabilities)

Throughout the sequence, students did a very nice job of following reactions by TLC. Atno point did I find evidence that a student “allowed the reaction to go for an hour,

because that is what the book said to do”. This is a very important skill for students to

learn, and one that I find difficult to teach even in my senior level students. Additionally,

the yields for most students were in the 50-80% range- consistent with the reactionsperformed by novice chemist- that required the students to think about and carry out

separations, although most of the students picked recrystallization as their purification

method.

Most interesting to me was the incorporation of the reductive coupling reaction using

dibutyl zirconocene and two equivalents of the nascent di-aromatic acetylene. Within

these lab reports I found the students to have quite a sophisticated understanding of the

techniques that they were using and that they were able to accomplish thecharacterizations of the sometimes very sensitive zirconacycles. One of the students

reports had a good spectrum of tetraphenyl zirconacyclopentadiene, show only a small

amount of a second set of Cp rings and most importantly, it did not show any evidence ofoxidative degradation in the Cp region (no Cp grass…). This suggests that the studentlearned the air sensitive handling techniques quite well and is in possession of fairly

sophisticated laboratory techniques quite early in her education. The write-ups of the

procedures confirmed that most of the students understood what they wee doing at the

glove box and from what I read, they should be able to repeat the techniques in futureyears.

Several questions arose while I read the reports that might be addressed during futureimplementations of this sequence. First, why were groups of three chosen? In some lab

reports it seemed that one of the partners was the one who did most of every reaction and

that the others were simply watching. While this might be a function of having labreports for only one of their reactions in the sequence, some care might be needed toassure that all of the partners are participating at the same level. Second, some spectral

interpretation seemed lacking across the board. Since the sequence involves a

preliminary training run through each reaction, some time might be allotted early to the

introduction of interpretation of NMR especially. I suspect that the NMR interpretationwould have been much easier if a high field NMR was available for the students to use as

well-- some of the aromatic regions had a jumble of overlapping resonances that made it

difficult to see if the material was impure or was suffering from higher order splitting

with overlapping resonances. A third area was the issue of purification- whilecrystallization is the way to go for most solid compounds, the students reported very

good separations by TLC, which suggests that introduction of small scale flashchromatography might be a extra technique to incorporate within this sequence.

These concerns noted I still find that this is an ingenious and viable exploratory lab

sequence for the sophomore organic lab course. It allows motivated students to explore

with a variety of starting materials (non symmetric alkynes resulting from their choice of

Wittig coupling partners) and to use as much spectroscopic information as they want toidentify their product. It also allows all of the students to participate- albeit in a small



way- in an active research program that requires advanced experimental techniques. I

will tell you that I have included these reactions as an option within my organic coursethis spring.

Richard Broene

Associate Professor of Chemistry

Bowdoin College

Brunswick, ME 04011



Student Report September 9 and 16, 2004

Preparation of Benzyltriphenylphosphonium bromide

+Br

(C6H

5)3P (C6H5)3P

+Br

-

Materials FW Amount mmol

Triphenylphosphine 262 0.2989 g 1.14

Benzyl bromide 171 142 µL 1.20

Procedure:I measured out 0.2989 g triphenylphosphine, or the equivalent of just over 1 mmol. I

added this white powder to a 10-mL round-bottom flask which already contained about 5mL

toluene. The benzyl bromide in this reaction is meant to be the excess reagent by 5%.

Accordingly I measured 142 µL of liquid benzyl bromide, which corresponds to 1.20 mmol.

I emptied the eppendorf pipette into the reaction vessel and attached it to a reflux condenser.I set the reaction vessel in a sand bath and ensured that the temperature did not drop below

110ºC. The temperature actually fluctuated from 110ºC to above 150ºC. Almost

immediately after mixing the two reactants I witnessed the formation of a white precipitate.

The benzyltriphenylphosphonium bromide product (a salt) is insoluble in the non-polar

toluene solvent. I heated the reaction mixture for about an hour and observed that the

amount of white precipitate increased over time.

I prepared several TLC plates during the reaction but was unable to determine whether

the reaction was complete. This was due to poor technique, perhaps. In any event, the

precipitate provided enough proof that the reaction had progressed.

After setting aside the capped reaction vessel for a week I performed another TLC using

100% hexanes. Triphenylphosphine and benzyl bromide both showed up in the reaction

mixture lane, with R f values of 0.29 and 0.45 respectively. The triphenylphosphine spot wasfainter than that for benzyl bromide but the reaction could not be said to be complete as the

limiting reagent was not used up. I decided that I would not continue to heat the mixture to

drive the reaction to completion, though, because I had plenty of precipitate for the infrared

analysis.

I performed a vacuum filtration to isolate the precipitate. Mass by difference using the

Hirsch funnel gave a mass of 312 mg and a percent yield of 63%. The melting point range of

the product was 294 - 297 ºC. I recorded the IR spectrum of the product.

Analysis of Spectral Data:IR Spectrum

I obtained the IR spectrum of my product which is shown in Figure 1. There were

bands at 2851 and 2882 cm-1

, which I assigned to methylene stretches. I assigned the band at1484 cm-1 to the symmetric deformation of the methylene group. The fours bands I expected

for arene C=C stretching, !8a, !8ba, !19a, and !19b, appeared at 1602, 1585, 1500, and 1435 cm-

1, respectively. These values compare favorably to those listed on page 155 of Microscale

Techniques for the Organic Laboratory1. I assigned a strong band at 691 cm-1 to the

1 Microscale Techniques for the Organic Laboratory, second edition. Authors: Mayo, Dana W.; Pike,

Ronald M.; Trumper, Peter K. John Wiley and Sons, Inc. © 2001.



aromatic C=C out-of-plane ring deformation. Finally, I assigned the out of plane C-H bend

to the band at 755 cm-1; the expected region for this band is between 730 – 770 cm-1.

Figure 1

The IR Spectrum of benzyltriphenylphosphonium bromide



Student Report

Preparation of Diphenylacetylene

Br

Br

2KOH+

!H

triethyleneglycol

2H2O

2KBr +

Materials FW Amount mmol R f

meso-stilbene dibromide 340 360.0 mg 1.06 0.33

KOH (85 wt%) 56 157 mg 2.38 ----

triethylene glycol (bp 285°C)

(solvent)---- 500 µL ---- ----

diphenylacetylene

(product)178 87 0.489 0.52

Procedure:I measured out 0.3600 g meso-stilbene dibromide: this is 1.06 mmol. I added this white

crystalline powder to a 13 x 100 mm test tube which already contained about 0.5 mL

triethylene glycol. This solvent was selected for its unusually high boiling point. I then added

157 mg of the KOH pellets, which, given that it is 85 wt% KOH (the rest being water), is

really 133 mg or 2.38 mmol. I mixed these three substances together with a high-temperature

thermometer and set the test tube in a hot sand bath to heat.

Almost as soon as I heated the mixture it turned brown and began to bubble as the water

in the KOH boiled away. The mixture continued to bubble as water formed in the reaction. I

heated the mixture to a temperature of about 170 ºC and watched as it homogenized and bubbled gently. I allowed it to react and heat until it had stopped bubbling for about five

minutes.I prepared a TLC plate using a 5:1 mixture of hexanes and methylene chloride. The TLC

plate clearly indicated that the desired product had formed in the reaction mixture. The

reaction mixture lane showed a spot at the same R f (0.52) as the store-bought

diphenylacetylene and no spot at the R f of the meso-stilbene dibromide.

I performed a vacuum filtration to isolate the precipitate, which is the crude product. The

mass by difference, using the Hirsch funnel, gave me a mass of 87.0 mg and a percent yield

of 46%. I attempted to re-crystallize the crude product using hot ethanol but found that itappeared to be completely soluble in both hot and cold ethanol. In consultation with the

professor I added some cold de-ionized water since diphenylacetylene is completely

insoluble in water. This and cooling the flask in an ice-water bath caused rapid

crystallization. I centrifuged the solvent away several times, having some difficulty due to a

cracked Craig-tube. The final yield of re-crystallized diphenylacetylene was 31.1 mg.The melting point range of the crude product was 52 - 58 ºC. The melting point range of

my re-crystallized product was smaller: 56 - 58 ºC. This shows that my re-crystallization was

successful in isolating a pure product from the crude yield of the reaction. I also determined

the melting point range for an authentic sample: 52 - 54ºC. Comparing this to the values

given in the Aldrich catalog revealed a small difference which I attribute to a miscalibration

of the thermometer. Aldrich reports a range of 59 - 60 ºC. I recorded the IR spectrum (fig. 1),1H NMR (fig. 2) and GC-MS (figs. 3 - 8) of the product.



Analysis of Spectral Data:IR SpectrumI obtained the IR spectrum of my product which is shown in Figure 1. The

lack of a group frequency band at 2225 cm-1, which represents the C=C stretch mode,could be taken

as indirect evidence of a symmetrical acetylene. Though by no means conclusive this

is at least consistent with the expected product of the reaction performed. I assigned

the band at 756 cm-1 to the arene C-H out-of-plane bending (5H). The fours bands I

expected for arene C=C stretching, !8a, !8ba, !19a, and !19b appeared at 1597, 1570,

1493 and 1443 cm-1, respectively. These values compare favorably to those listed on

page 155 of Microscale Techniques for the Organic Laboratory2. I assigned a strong band at 690 cm-1 to the aromatic C=C out-of-plane ring deformation.

Figure 1

The IR Spectrum of Diphenylacetylene

2 Microscale Techniques for the Organic Laboratory, second edition. Authors: Mayo, Dana W.; Pike,

Ronald M.; Trumper, Peter K. John Wiley and Sons, Inc. © 2001.



NMR SpectraI prepared an NMR analysis tube containing 5 mg of an authentic sample of

diphenylacetylene in ~700 µL CDCl3 containing TMS to collect an 1H NMR spectrum.

There is a region of tightly spaced resonances between 7.25 and 7.46 ppm: these are due to

the H atoms on the phenyl rings. A singlet at 2.13 ppm is due to the H atoms of acetone: I

cleaned the NMR tube using acetone and apparently it had not all evaporated before I added

my sample.

Figure 2

The 1HNMR Spectrum for Diphenylacetylene

Gas Chromatography/Mass SpectrometryI collected a gas chromatogram and mass spectrum for my

own diphenylacetylene product. Diphenylacetylene had a

retention time of 5.83 minutes. The mass spectrum had a base

peak at 178.1 m/z, which is the molecular ion. A library search

for gave diphenylacetylene as the most likely substance.

A gas chromatogram of my crude product (figure5) showed

three substances, with one substance predominating. The peak at

a retention time of 5.41 was the desired diphenylacetylene

product according to that peak’s mass spectrum (figure 6). Theseries of peaks at RT 5.83, 5.93 and 5.97 had identical mass

spectra; of these the mass spectrum for the peak at 5.97 minutes is

shown. A library search showed a substance that matches this

mass spectrum (figure 7) with 82%. The substance is shown in

drawing form on the mass spectrum and appears to be a

combination of two stilbene molecules which occurred after the

first (successful) dehydrobromination.

The last product’s mass spectrum (figure 8) is more difficult to

identify and explain. The library search found a match with only



70% probability and it is depicted on the mass spectrum. If this is

in fact a good identification of the substance the only explanation

for its presence that I can offer is that perhaps during the course

of making thin-layer chromatography plates some of the silica

substrate made its way into the reaction vessel. RT: 4.00 - 8.00

4.0 4.5 5.0 5.5 6.0 6.5 7.0 . .

Time (min)

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

5.83

6.05

6.11 6.195.20 5.30 5.695.17

5.024.93

4.734.534.08

:

.

I _

AK16a_041102103026 #195 RT: 5.83 AV:1 NL: 1.31E6

T: + c Full ms [ 40.00-550.00]

50 100 150 200 250 300 350 400 450 500 55

m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

178.1

176.1

152.1

179.1

151.176.1207.0126.198.163.0

209.0 253.0 281.0 298.7 327.0 390.8 427.1 467.1

Figure 3

The Gas Chromatogram for Diphenylacetylene

Figure 4

The Mass Spectrum for Diphenylacetylene

RT: 4.50 - 7.00

4.6 4.8 5.0 5.2 5.4 5.6 5.8 6.0 6.2 6.4 6.6 6.8

Time (min)

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

5.97

5.93

5.83

5.41

6.66

6.195.16 6.976.926.25 6.545.375.09 6.734.984.744.69

NL:

8.20E6

TIC MS

ak.crude.di

phenylacet

ylene

ak.crude.diphenylacetylene #150 RT: 5.40 AV:1 NL: 3.93E5

T: + c Full ms [ 40.00-550.00]

80 100 120 140 160 180 200 220

m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

178.1

176.1

152.2

179.2 207.076.1

150.189.2 126.2

149.2 209.0139.187.1 193.298.1 153.2102.1 165.2122.1 180.1 22197.1 210.3

Figure 5

The Gas Chromatogram for my Crude Diphenylacetylene

Figure 6

The Mass Spectrum for Crude Diphenylacetyle



Figure 7

The Mass Spectrum for Crude Diphenylacetylene (RT 5.97)

Figure 8

The Mass Spectrum for Crude Diphenylacetylene (RT 6.66)

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