Inductive effects of an alkyl group:

The chlorine atoms encompass an electron-withdrawing effect on the negative charge that helps to stabilize it. If the negative charge is stabilized, it creates the conjugate base that is less reactive and a weaker base.

 Note: The conjugate base of a strong acid is weak, where as the conjugate base of a weak acid is strong. Hence, the order of basicity for the ethanoate ions Cl₃CCO₂, Cl₂CHCO₂, ClCH₂CO₂, and CH₃CO₂ is the reverse to the order of acidity for the corresponding carboxylic acids, i.e. the ethanoate ion is the strongest base, whereas the trichlorinated ethanoate ion is the weakest base.

Inductive effects as well affect the basic strength of neutral molecules (for example amines). The pK_b for ammonia is 4.74 that compares with pK_b values for methylamine, ethylamine, and propylamine of 3.36, 3.25 and 3.33 correspondingly. The alkylamines are stronger bases as compared to the ammonia due to the inductive effect of an alkyl group on the alkyl ammonium ion (RNH₃⁺). Alkyl groups donate electrons in the direction of a neighboring positive center and this assists to stabilize the ion because some of the positive charge is partially dispersed on the alkyl group. If the ion is stabilized, the equilibrium of the acid-base reaction will shift to the ion that means that the amine is more basic. The larger the alkyl group, the more important this effect.

If one alkyl group can affect the basicity of an amine, after that further alkyl groups should have an even greater inductive effect. Hence, one might expect secondary and tertiary amines to be stronger bases as compared to the primary amines. Actually, this is not essentially the case. There is no easy relationship among the basicity and the number of alkyl groups attached to nitrogen. Even though the inductive effect of more alkyl groups is specifically greater, this effect is counter balanced through a solvation effect.

Figure: Inductive effects of an alkyl group on the alkyl ammonium ion.