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Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: IA97 on September 27, 2020, 07:47:31 PM

Title: IR spectra of trans-cinnamic acid vs methyl trans-cinnamate
Post by: IA97 on September 27, 2020, 07:47:31 PM

I am comparing the IR spectra of methyl trans-cinnamate and trans-cinnamic acid. For the IR spectrum of methyl trans-cinnamate, aromatic overtones can be seen (2112 cm^-1, 1995 cm^-1, and 1923 cm^-1), while they are not present in the IR spectrum of trans-cinnamic acid. Both of these molecules contain the same aromatic ring, so how come only one of them contains the aromatic overtones? I have attached the relevant spectra. Any help would be much appreciated, thank you!

Title: Re: IR spectra of trans-cinnamic acid vs methyl trans-cinnamate
Post by: Babcock_Hall on September 28, 2020, 08:15:57 AM

I am not sure of the answer, but I do see weak, unlabeled peaks in the cinnamic acid spectrum in this vicinity.