Interpret these two NMR spectra for ethyl acetoacetate as: (a) neat liquid (b) a

Question

Interpret these two NMR spectra for ethyl acetoacetate as:

(a) neat liquid

(b) a 10% (v/v) solution in CCl4

1.) Calculate the percentage of enol form in each case, show all working.
2.) Explain the effect of the solvent on the percentage.

Lecturer said to:

Start by working out what the NMR spectrum should look like for the enrol form and the keto form. How many peaks should there be, what relative heights, splitting etc.

Then analyse the two spectra that you have.

There are three possibilities:

1) a spectrum with all keto form

2) a spectrum with all enol form

3) a spectrum with a mixture of enol and keto form.

If one of the spectra doesn't correspond to pure enol or keto then it is probably a mixture.

Then see if you can find peak height that WILL NOT be affected by the keto/enol change (i.e. is the same in ALL possible spectra) and look at the heights of a peak that you can unambiguously assign to the enol form. The relative heights will allow you to calculate the % enol. Make sure you account for how many hydrogens are expected for each of these peaks.

Explanation / Answer

1.a The enol percentage in fig-1 is zero it is totally keto form

1.b The second figure contains 40% of enol form against Keto form

2. In solvent the enolisation is fast compoared with neat form. If the solvents which are slightly acidic can make the compound enolize very quickly. Usually CCl4 is having slightly acidic in nature which makes ethylaceto acetate to enol form from its keto form

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