Final answer:
In an SN2 reaction, the nucleophile displaces the leaving group from the substrate, creating a new chemical bond accompanied by an inversion of stereochemistry. An example is the O-methylation of alcohol with methyl iodide, resulting in an ether and iodide ion as products.
Step-by-step explanation:
Understanding SN2 reactions is fundamental in organic chemistry. For these reactions, we identify the nucleophile, which is the species that donates electrons to the substrate; the substrate, typically an alkyl halide, which is the molecule being attacked; and the leaving group, which is the portion of the substrate that is displaced by the nucleophile. In an SN2 reaction, the nucleophile attacks the electrophilic carbon atom from the side opposite the leaving group, leading to its displacement and formation of a new bond in one concerted step. The result is an inversion of stereochemistry at the carbon atom.
For example, in the O-methylation of an alcohol using methyl iodide, the oxygen atom of the alcohol acts as the nucleophile, the methyl iodide is the substrate, and the iodide ion is a very good leaving group. Following the reaction, we obtain an ether as the organic product and iodide as the inorganic product. This process illustrates how learning examples of SN2 reactions, such as those involving alcohols, ethers, amines, and thiols, helps grasp the concept of nucleophilic substitutions.