Question

The acid-catalyzed dehydration of 1-methylcyclohexanol yields a mixture of two alkenes. How could you use ${}^1\mathrm{H}$NMR to help you decide which was which?

Short answer

The two isomers are distinguished by the ${}^{13}\mathrm{C}$NMR.

Isomer a: have only single by vinylic proton

Isomer b: have single due to methyl signal and vinylic signal

Step-by-step solution

13C NMR

Carbon-13 nuclear magnetic resonance is a technique similar to the NMR which is used to identify the carbon from the organic molecules or from the organometallic compounds like hydrogen is detected in NMR but it’s only sensitive to carbon-13, not carbon-12.

Isomer A

Isomer a has four different kinds of protons as per symmetry. Its vinylic carbon has two protons which show absorption at 4.5 -6.5.

Isomer B

Isomer b has six different kinds of protons as per symmetry. Its vinylic proton and the methyl proton which produce different signals and the methyl group signal does not split so, based upon a number of protons and signals the two isomers are separated.