CHEM 102 Lecture Notes - Lecture 8: Leaving Group, Nucleophile, Elimination Reaction
Document Summary
You have just seen molecules bearing leaving groups being attacked at two distinct electrophilic sites: the carbon to which the leaving group is attached, and the hydrogen atoms on the carbon adjacent to the leaving group. Attack at carbon leads to substitution; attack at hydrogen leads to elimination. Since strong bases attack protons, it is generally true that, the more basic the nucleophile, the more likely that elimination is going to replace substitution as the main reaction of an alkyl halide. Here is an example of this idea at work. For a nucleophile, attacking a carbon atom means squeezing past its substituents and even for unhindered primary alkyl halides there is still one alkyl group attached. This is one of the reasons that sn2 is so slow on hindered alkyl halides the nucleophile has difficulty getting to the reactive centre. One of the best bases for promoting elimination and avoiding substiutution is potassium t-butoxide.
