The mechanism of a nucleophilic substitution reaction between an alkyl halide and an alcohol in the presence of a base is typically an SN2 Substitution Nucleophilic Bimolecular or SN1 Substitution Nucleophilic Unimolecular reaction, depending on the structure of the alkyl halide and the reaction conditions. Here, I will describe both mechanisms.SN2 Mechanism:1. The base deprotonates the alcohol, generating an alkoxide ion RO- as the nucleophile.2. The alkoxide ion attacks the electrophilic carbon atom of the alkyl halide from the opposite side of the leaving group halide ion, X- .3. The bond between the electrophilic carbon and the leaving group breaks, and the halide ion leaves simultaneously as the alkoxide ion forms a bond with the carbon.4. The product is an ether, formed through a concerted, single-step process with stereochemistry inversion at the electrophilic carbon.SN1 Mechanism:1. The base deprotonates the alcohol, generating an alkoxide ion RO- as the nucleophile.2. The bond between the electrophilic carbon and the leaving group halide ion, X- breaks, forming a carbocation intermediate and a halide ion.3. The alkoxide ion attacks the carbocation, forming a bond with the electrophilic carbon.4. The product is an ether, formed through a two-step process with racemization at the electrophilic carbon.The SN2 mechanism is favored for primary alkyl halides, while the SN1 mechanism is favored for tertiary alkyl halides. Secondary alkyl halides can undergo both mechanisms, depending on the reaction conditions and the nature of the nucleophile and leaving group.