Experiment 6: Elimination Reactions (E1/E2)

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Elimination Reactions

Due Dates:

15 Mar / 16 Mar A/B

 

Chemical Safety Information:

E1
2-methyl-2-butanol sulfuric acid 2-methyl-1-butene
2-methyl-2-butene deuterated chloroform  
E2
2-chloro-2-methylbutane 1-propanol potassium hydroxide

 

Experimental Spectra:

E1

2-methyl-2-butanol 1H-NMR FID (FOR REFERENCE ONLY)

Stock FID 1H-NMR E1 Reaction of 2-methyl-2-butanol (available for submission for credit, see laboratory manual for details)

Sample 1H-NMR E1 Reaction of 2-methyl-2-butanol (not available for submission for credit)

Stock GC/MS E1 Reaction of 2-methyl-2-butanol (available for submission for credit, see laboratory manual for details)

E2

2-chloro-2-methylbutane 1H-NMR FID (FOR REFERENCE ONLY)

Sample 1H-NMR E2 Reaction of 2-chloro-2-methylbutane (not available for submission for credit)

Stock FID 1H-NMR E2 Reaction of 2-chloro-2-methylbutane (available for submission for credit, see laboratory manual for details)

Stock GC/MS E2 Reaction of 2-chloro-2-methylbutane (available for submission for credit, see laboratory manual for details)

 

Frequently Asked Questions:

Q1) How do I calculate the ratios of two different molecules in an 1H-NMR spectrum?

A1) The integral of each 1H-NMR signal is relative to the number of equivalent 1H-nuclei in the sample that generates that signal.  This information can be used to calculate the ratio of two or more molecules in the same spectrum, assuming that the spectrum contains at least one adequately resolved signal for each molecule.  The handout (linked below) contains an example of how to correctly perform such a calculation.  The oxidation reaction used in the handout produces both ethyl cinnamate (Product A) and ethyl 3-​phenylpropionate (Product B).

HANDOUT - Calculating product ratios from 1H-NMR data

Q2) How do I handle an output structure for the product calculation in WebMO if it is a transition state and not an energy minimum?

A2) First, find out what is wrong with the structure.  This can be done by visualizing the negative vibrational mode in WebMO.  For a simple molecule like this, it is almost certainly a negative mode associated with a rotating methyl group as shown below.  This issue can be fixed in several ways.  The easiest method is to simply rotate the methyl group into a different orientation and resubmit the job.  Remember that if a clean-up option rotated the methyl group poorly, you may not want to clean this molecule with the same tool (or at all) the second time.

Negative Vibrational Modes Indicate Transition States

Q3) How do I figure out whether a reaction is thermodynamically controlled or kinetically controlled?

A3) You need to know at least two things in order to answer this question and understand the outcome of a particular reaction.  First, know the mechanism of the reaction and the potential energy surface associated with it.  Second, know the conditions under which the reactions is run, specifically whether or not the reaction reaches equilibrium.  If the reaction reaches equilibrium then the product ratio will be based upon the relative energies of the products.  If the reaction is irreversible then the product ratio will be based upon the relative energies of the transition states leading to each product.