Question

IR spectroscopy question: I have two shorter bumps at 3460 and 3309 cm -1 and I know this is supposed to be benzene? the product we were supposed to make in lab was 6-ethoxycarbonyl-3,5-diphenyl-2-cyclohexenone. If you could just go over the major functional groups and an estimation of where the absorptions should be for this molecule so I can compare it to my IR spectrum. Tried to put IR spectrum of my product up but it is blurry like every other time I try to upload a photo with a question.

Answer 1

Answer – We are given the 6-ethoxycarbonyl-3,5-diphenyl-2-cyclohexenone and need to look for the major functional group with IR spectra.

We know the following is the structure for the 6-ethoxycarbonyl-3,5-diphenyl-2-cyclohexenone –

In this structure there is ketone, ester and alkene are the major functional groups.

We know ketone carbonyl are show at 1705-1725 cm^-1, but in this one there is ketone carbonyl is conjugate with double bond, so it is on at 1700 cm^-1.

Ester carbonyl at 1735-1750 cm^-1, so there are two peak between 1700-1740 cm^-1.

Alkene, means C=C show at 1620-1680 cm^-1

Benzene C=C at 1500-1600 cm^-1.

The Aromatic C-H 3000-3100 cm^-1.

The alkene hydrogen C=C-H is at 3010-3100 cm^-1.

So above are the all major peaks, so short 3460 and 3309 cm^-1 is for the solvent or other impurities, but it is not for benzene.