1) The document summarizes different reaction mechanisms for nucleophilic substitution including SNi, SN1', SN2', SN1cA, and SN2cA. 2) SNi involves nucleophilic substitution with retention of configuration where part of the leaving group attacks. 3) SN1' occurs with allylic substrates under SN1 conditions producing normal and rearranged products due to resonance of the allylic carbocation. 4) SN2' is an allylic rearrangement that can occur under SN2 conditions where the nucleophile attacks the γ-carbon. 5) SN1cA and SN2cA involve a preliminary protonation step to convert a non-leaving