Final answer:
The SN1 reaction is unimolecular and typically occurs with tertiary alkyl halides, while the SN2 reaction is bimolecular, involving the concerted action of a nucleophile and a substrate, and generally occurs with primary or methyl substrates. Both reaction orders are influenced by substrate structure, nucleophile, leaving group, and solvent.
Step-by-step explanation:
SN1 and SN2 Reaction Orders
The orders of SN1 and SN2 reactions refer to the molecularity of each type of reaction. The SN1 reaction is unimolecular, meaning that its rate is determined by the concentration of only one reactant, typically the substrate.
This type of reaction usually occurs with tertiary alkyl halides and can lead to a racemic mixture due to the formation of a carbocation intermediate that the nucleophile can attack from either side.
On the other hand, the SN2 reaction is bimolecular, involving concerted bond breaking and formation, and its rate is affected by the concentration of two reactants: the nucleophile and the substrate.
The SN2 mechanism is characterized by a backside attack where the nucleophile approaches the electrophilic carbon opposite to the leaving group. It generally occurs with primary or methyl substrates.
The choice between SN1 and SN2 mechanisms is influenced by factors such as the substrate structure, the strength and steric hindrance of the nucleophile, the leaving group, and the solvent.
While SN2 reactions are favored in polar aprotic solvents and with less hindered substrates, SN1 reactions are preferred in polar protic solvents and with more hindered substrates.