Question

2. How would Evelyn Effec affect the products formed from the dehydration of 2-methylhexanol (My product is 1-methylcyclohexene)? How could you modify the experiment to check for the Evelyn Effect?

Answer 1

Solution:

Acid (H₃PO₄) catalyzed dehydration of 2-methylcyclohexanol is believed to occur by an E₁ mechanism involving protonation of the hydroxyl group, loss of water to for, a carbocation intermediate, and loss of a proton to generate the product which usually follows Zaitzev's rule. Hence the dehydration should result in 1-methylcyclohexene only. However, the observation was such that the reaction resulted in products (A), (B) & (C). Refer scheme (1) in the image.

The outcome brings us to the Evelyn effect. 2-methylcyclohexanol is nearly an equimolar mixture of cis and trans isomer. The cis isomer undergo dehydration faster than trans isomer. Further, the cis isomer undergo E₁ elimination and give the product (A), as per Zaitsev's rule. Refer scheme (2) in the image. The trans isomer undergo E₂ elimination and gives the product (A) & product (B). Refer scheme (3) in the image. Product (C) might be as a result of E₁ involving a carbocation rearrangement via hydride shift. Refer scheme (4) in the attached image.

To check for the Evelyn effect, follow the progress of the reaction by measuring the volume of 1-methycyclohexene in the distillate. Further, collect two fractions of approximately equal volume and check the composition of (A), (B) & (C) in both the fractions. Based on the outcome conclusion can be made.