Chapter 7.8, Problem 7.17E

Interpretation Introduction

Interpretation: The reason behind greater proportions of elimination products favored at higher reaction temperature should be explained.

Concept introduction: Three principal factors that affect the competition between substitution and elimination: basicity of the nucleophile, steric hindrance in the alkyl halide, and steric bulk around the nucleophilic atom. The bases such as hydroxide ion, alkoxide ion, amide ion, tertiary amines are highly strong bases that favor elimination over substitution. On the other hand bases such as methanol, halides, alkyl phosphines, azides, cyanides, acetates are regarded as weak bases and they form substitution product in greater ratios than elimination products.

Nucleophiles that have large steric bulk such as $\text{potassium tert-butoxide}$ , $\text{LDA}$ lithium diisopropylamide favor elimination predominantly and form substitution product in minor or negligible amount. On the other hand, nucleophiles that are not sterically hindered such as ${\text{CH}}_{\text{3}}{\text{O}}^{-}$ , ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{O}}^{-}$ , ${\text{H}}_{\text{2}}{\text{N}}^{-}$ , ${\text{HO}}^{-}$ favor some degree of substitution also.