Question

The following questions refers to the synthesis of methylcyclohexenes from 2-methylcyclohexanol:

Q.1) Why do we only use simple distillation??

Answer: I think it's something regarding Le's Chatelier's principle, i.e, to move the equilibrium of the reaction to the right side of the reaction formula. Is this correct? Or is there more to this?

Q.2) Why do we use gc and gcmas, instead of nmr?

Answer: because gc and gcmas gives the ratio of the various isomeric products, i.e gives their purity-this can't be achieved through nmr sprectroscopy. Is this correct?

Q.3) Why do use IR spectroscopy?

Answer: To verify if any starting material is still present. Since, it's a reversile reaction, there is a good chance that some amount of starting material will be present. Is this correct?

Thank you so much! :D

Answer 1

1. Yes, it follows Le Chartelier's principle. The isolation of methoxyhexene by distillation will shift the equilibrium towards product side. (Also, the boiling point of alcohol and water are higher than methylcyclohexene).

2. No, NMR can show purity, but the relaxation time for unequivalent protons are different. Thus, in calculating ratio, equivalent protons should be taken into consideration. A little variation can lead to change in product ratio. However, in GC/GCMS the ration can be calculated directly and correctly.

3. Yes, IR is done to check the purity of product. It should not contaminated with alcohol as the reaction is reversible. For alcohol, a broad O-H stetching will be found around 3500-3300 cm-.