Increasing the number of alkyl substituents generally stabilizes carbanions and carbocations due to hyperconjugation and inductive effects, which help distribute charge more effectively. For carbon-centered radicals, the stabilization also occurs, but to a lesser extent compared to carbocations. The presence of alkyl groups reduces electron density around the positively charged center, enhancing stability. Conversely, for carbanions, increased steric hindrance from substituents can lead to destabilization if the groups are bulky. Overall, the impact of substituents on these intermediates is primarily linked to their ability to stabilize or destabilize charge distribution.
