Experiment 9: Wittig Synthesis of Ethyl Cinnamate

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Wittig Synthesis

Due Dates:

24 Apr / 25 Apr A/B

 

Chemical Safety Information:

Reagents and Solvents
benzaldehyde methanol (carbethoxymethylene) triphenylphosphorane
magnesium sulfate deuterated chloroform ethyl cinnamate

 

Experimental Spectra:

Sample 1H-NMR ethyl cinnamate (not available for submission for credit)

Stock 1H-NMR FID ethyl cinnamate solvent-free (available for submission for credit, see laboratory manual for details)

Stock 1H-NMR FID ethyl cinnamate with MeOH (available for submission for credit, see laboratory manual for details)

Stock 1H-NMR FID ethyl cinnamate with iPrOH (available for submission for credit, see laboratory manual for details)

Stock GC-MS ethyl cinnamate solvent-free (available for submission for credit, see laboratory manual for details)

Stock GC-MS ethyl cinnamate in MeOH (available for submission for credit, see laboratory manual for details)

Stock GC-MS ethyl cinnamate in iPrOH (available for submission for credit, see laboratory manual for details)

 

Frequently Asked Questions:

Q1) How do I pronounce Wittig?

A1) The Wittig reaction is named after its discoverer Georg Wittig who was awarded the Nobel Prize in Chemistry in 1979.  As a German language name, the W in Wittig should be pronounced like a V in English.

Q2) How do I calculate the ratios of two different molecules in the same 1H-NMR spectrum?

A2) The integrals of each signal are relative to the number of 1H-atoms in the sample that are responsible for that signal.  This can be used to find the ratio between two or more molecules in the same spectrum, given that the peaks for each molecule can be resolved cleanly.  The link below contains an example of how this is done correctly.

Calculating Product Ratios by 1H-NMR

Q3) What is the best/lowest energy conformation of the carboxylate group in ethyl cinnamate or cinnamic acid?

A3) Choosing the correct dihedral angle for the carboxylate group is important to get the lowest energy or most stable conformation.  For carboxylic acids and esters, two stable conformers (anti and syn) exist with the syn being the most stable.  Shown below are two comparisons for these conformations of ethyl acetate and acetic acid calculated at the B3LYP/6-31G(d) level.

  syn acetic acid anti acetic acid syn ethyl acetate anti ethyl acetate
  syn acetic acid anti acetic acid syn ethyl acetate anti ethyl acetate
Relative Energy (kcal/mol) 0.0 6.0 0.0 7.4