1) Consider the dehydration reaction of 4-methylcyclohexanol. Consider a stabili

Question

1)

Consider the dehydration reaction of 4-methylcyclohexanol. Consider a stability of relevant conformations required for E2 elimination and predict which stereoisomer should undergo dehydration faster, if we assume that both E1 and E2 occurs concurrently: cis or trans-4-methylcyclohexanol?

2)

Suppose you used sulfuric acid instead of phosphoric acid for dehydration of 2-- methylcyclohexanol. For which acid do you expect the higher contribution of E2 mechanism and why? (pKa of sulfuric acid -9).

3)Propose a reliable mechanism for the following reaction:  

Explanation / Answer

1) Relavent conformation for E2 elimination of 4-methylcyclohexanol is diequitorial trans conformation.

Trans isomer will undergo E2 dehyration faster.

2) We expect higher contribution for E2 mechanism for phosphoric acid. In the transition state of dehydration bond between oxygen and phosphorous is involved where as in sulphuric acid this is not seen. Sulphuric acid donates proton to OH group.

3)

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