Organic Chemistry: Structure and Function
Organic Chemistry: Structure and Function
8th Edition
ISBN: 9781319079451
Author: K. Peter C. Vollhardt, Neil E. Schore
Publisher: W. H. Freeman
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Chapter 7.9, Problem 7.22E

(a)

Interpretation Introduction

Interpretation: Out of the substrates for the below reactions the one pair that will give a higher E2:E1 product ratio should be identified.

  Organic Chemistry: Structure and Function, Chapter 7.9, Problem 7.22E , additional homework tip  1

Concept introduction: Carbocation formation is relatively slower than acid-base reactions. Carbocations generated from alkyl halides have two fates; they can be either trapped by nucleophiles to give substitution product or may deprotonated to yield small amount of alkene. Stronger the base more is the probability of elimination over substitution over elimination. Further, if still higher concentration is employed reaction proceeds via bimolecular elimination. On the other hand, weak base waits until the carbocation is formed and the type of elimination with relatively weak base is two-step elimination or E1 .

Analogous to the case that strong nucleophiles are more favored to react via SN2 pathway, greater concentration of strong bases are more favored for single-step elimination E2 pathway. Such strong bases include hydroxide ion or alkoxide ions. The reason of predominance of E2 elimination is that strong bases have high probabilities and high rates to abstract hydrogen from carbon adjacent to carbocation.

(b)

Interpretation Introduction

Interpretation: Out of the substrates for the reactions the one pair that will give a higher E2: E1 product ratio should be identified.

  Organic Chemistry: Structure and Function, Chapter 7.9, Problem 7.22E , additional homework tip  2

Concept introduction: Carbocation formation is relatively slower than acid-base reactions. Carbocations generated from alkyl halides have two fates; they can be either trapped by nucleophiles to give substitution product or may deprotonated to yield small amount of alkene. Stronger the base more is the probability of elimination over substitution over elimination. Further, if still higher concentration is employed reaction proceeds via bimolecular elimination. On the other hand, weak base waits until the carbocation is formed and the type of elimination with relatively weak base is two-step elimination or E1 .

Analogous to the case that strong nucleophiles are more favored to react via SN2 pathway, greater concentration of strong bases are more favored for single-step elimination E2 pathway. Such strong bases include hydroxide ion or alkoxide ions. The reason of predominance of E2 elimination is that strong bases have high probabilities and high rates to abstract hydrogen from carbon adjacent to carbocation.

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