Final answer:
In SN2 reactions common in organic chemistry, 'X' refers to the leaving group which is typically a halide, such as iodide in the O-methylation using methyl iodide. The specific identity of 'X' will depend on the reaction and conditions. In different contexts, such as polymer chemistry, 'X' can represent different functional groups within the polymer.
Step-by-step explanation:
When discussing what can X be as a radical in Mechanism I, we are examining a nucleophilic substitution reaction mechanism, typically noted as an SN2 mechanism. The 'X' in this situation refers to a leaving group in a chemical reaction where a nucleophile ('N') displaces another group. In the context of a primary alkyl halide substitution, which is often the substrate in an SN2 reaction, the leaving group is generally a halide. For example, in an O-methylation reaction that uses methyl iodide (CH3 - I), the 'X' would be the iodide ion (I-), which is known to be a very good leaving group enabling the nucleophilic attack by the oxygen atom of an alcohol.
In other contexts, 'X' might refer to a different group depending on the substrate and reaction conditions. For instance, 'X' could be a chloride ion (Cl-) in an E1 reaction mechanism, as Cl- is known to be a stable anion that can serve as a leaving group. In the context of polymer chemistry, 'X' could represent a functional group attached to a monomer such as hydrogen in polyethylene, a methyl group in polypropylene, or a benzene ring in polystyrene.