In chemical reactions, the stability of leaving groups plays a crucial role in determining the feasibility of a reaction. In the comparison of two compounds, one with a methyl group (CH₃) and the other with a chlorine atom (Cl), the differences in leaving group ability become evident. Methyl groups are poor leaving groups because they do not stabilize negative charges effectively; thus, they are less likely to depart during a reaction.

On the other hand, chlorine is a much better leaving group due to its higher electronegativity and larger atomic size. Chlorine can stabilize a negative charge more effectively when it picks up electrons, making it a favorable candidate for leaving during nucleophilic substitution reactions. This is attributed to the element effect, where the inherent properties of chlorine allow it to be a superior leaving group compared to carbon-based groups.

In summary, the ability of a leaving group to stabilize a negative charge significantly influences reaction pathways. Chlorine, with its electronegativity and size, outperforms carbon-based leaving groups, making reactions involving chlorine more favorable and efficient.