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SolutionsAttack Geometry

1. Nucleophile or base?

The hydroxide ion, HO−, reacts with 2-bromopropane. Which product forms if it acts as a nucleophile? And if it acts as a base?

  1. As a nucleophile it attacks the carbon bonded to bromine and replaces it: propan-2-ol (substitution).
  2. As a base it removes a hydrogen from an adjacent carbon and bromide leaves: propene (elimination).

2. Attack from behind

In an SN2 substitution, why does the nucleophile approach from the side opposite the leaving group?

Because on that side the carbon is electron-poor and there is no repulsion with the electron density of the leaving group; besides, in this way it can form the new bond while the old one breaks.

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