Chem Post Lab

Name __________________________________ Student ID # ________________________

 

CHEM 308 REPORT FORM: Dehydrobromination of 2-Bromoheptane, Part 2

Submit at the beginning of next week’s scheduled lab

Alkoxide base

Simple Ratio

(1-heptene : trans-2heptene : cis-2-heptene)

Ratio of 1-Heptene :

2-Heptene

(both isomers)

2-Heptene

trans : cis Ratio

2-bromoheptane

(Lots, some, none; see instructions)

SN2 product

(Lots, some, none; see instructions)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Simple ratio calculation for ethoxide:

Name: _________________________________ Student ID # _________________

 

 

 REPORT FORM: Dehydrobromination of 2-Bromoheptane

Submit via Blackboard by 5 pm the day before your scheduled lab (must be a PDF file)

1.

1

Order the alkoxide bases in order of increasing steric demand (i.e., start with the least bulky and finish with the one with the most steric bulk near the O atom).

 

 

 

 

 

 

 

 

 

 

2.

3

How did the structure of the alcohol affect the ratio of 1-heptene to 2-heptenes (for this question, use the sum of cis– and trans-2-heptenes). Give a reason for this trend. Be specific and use numbers from the spreadsheet to support your answer.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3.

3

How did the structure of the alcohol affect the formation of SN2 products? Give a reason for this trend. Be specific and discuss the presence/absence of the SN2 product in the spectra of all of the alkoxide bases used in lab.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 1 of 2

4.

2

Comment on how the structure of the alkoxide base affects the ratio of trans-2-heptene to cis-2heptene. Is there a dramatic effect? Be specific and use numbers from the spreadsheet to support your answer.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5.

2

Did your reaction go to completion? Support your answer with evidence from the GC spectra. (Consider the group data for your alkoxide base to be representative of your reaction).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6.

2

One way of assessing whether the reaction has reached completion is to monitor the reaction by TLC. Suppose that when you TLC your reaction mixture (in a solvent system of 100% hexanes), both 2-bromoheptane and a mixture of heptene products are present.

 

Assuming that all heptene products appear as a single spot (due to similar polarities)…  Draw in the spots you would expect to see on the TLC template below.

 Label which spot corresponds to (a) 2-bromoheptane and (b) heptene isomers. (Make sure your relative polarities are correct!)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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CHEM 308 Organic Chemistry 1 Lab

Elimination Reaction Data Analysis

 

The GC data will have a series of peaks labeled with retention time (RT) and peak area (MA). Some peaks can be ignored, but you should pay attention to all peaks that have retention times and areas given. The approximate retention times for the expected compounds are given below, but note that the exact retention time can vary. Just like with other types of chromatography, the order that compounds elute does not change when the conditions are altered.

 

Approximate retention times

(in min.) …

Most likely identity

3.43

1-heptene

3.75

trans-2-heptene

3.95

cis-2-heptene

~8.5-10.5

SN2 products (normally only observed for reactions with NaOMe or NaOEt)

11.85

2-bromoheptane

 

Once the GC data for our class is posted, do the following:

  1. Use all of the spectra to complete post-lab part 2
  2. Use Part 2 of the post-lab to help you answer the questions in Part 1 Your Analysis:
  3. Print the spectrum for your assigned base only.
    1. On the spectrum, clearly draw the compound structure that corresponds to each peak.
      • There may be some slight variation in retention time (e.g., a peak expected at 2.24 min might show up at 2.20 or 2.27 min).
    2. If a peak from the table is NOT present in your spectrum (e.g., an SN2 product), you should still draw the structure and indicate approximately where that peak would have been expected.
  4. Fill out Part 2 of the Elimination Report Form (a Word document is provided on Blackboard if you would like to type your values in).
    1. For the ratio of 1-heptene to 2-heptene, you should sum the areas of the two 2-heptene peaks (e.g., 1-heptene : [trans-2-heptene + cis-2-heptene]).
    2. When writing ratios, the smallest component should be given the number “1”. All other numbers should be larger than 1 and reported with one decimal place.
      • For example:

2-Heptene

trans : cis Ratio

4.6 : 1

1 : 8.7

 

(not 1 : 0.22)

(not 0.11 : 1)

 

    1. The amount of SN2 Products and/or Starting Material (SM) should be reported as follows:
      • “Lots” if the height of the SN2 Product/Starting Material peak is the same as the height of the tallest elimination product peak.
      • “Some” if the height of the SN2 Product/Starting Material peak is smaller than the height of the tallest elimination product peak.
      • “None” if there is no peak visible where one would be expected for these materials (based on the retention times provided above).

Alkoxide base

Simple Ratio

(1-heptene : trans-2-heptene : cis-2-heptene)

Ratio of 1-Heptene :

2-Heptene
(both isomers)

2-Heptene

trans : cis Ratio

2-bromoheptane

(Lots, some, none;

see instructions)

SN2 product

(Lots, some, none;

see instructions)

      
      
      
      
      
      

CHEM 308 REPORT FORM: Dehydrobromination of 2-Bromoheptane, Part 2

Submit at the beginning of next week’s scheduled lab

Simple ratio calculation for ethoxide:

Order a unique copy of this paper
(550 words)

Approximate price: $22