The solvolysis reactions of ring-substituted benzylic and 1-propyl gem-diazides in water proceed by a stepwise mechanism through a-azido carbocation intermediates, which are captured by water to give the corresponding aldehyde as the sole detectable product. Rate constant ratios k(az)/k(s) (M(-1)) for partitioning of these carbocations between reaction with azide ion and reaction with water, determined by analysis of azide common ion inhibition of the solvolysis reaction, decrease from 8600 M(-1) for the relatively stable carbocation 4-MeOC(6)H(4)CH(N-3)(+) to 2 M(-1) for the highly unstable CH3CH2CH(N-3)(+). Rate constants k(s) (s(-1)) for reaction of these carbocations with solvent water, and equilibrium constants K-az = k(solv)/k(az) (M) for their formation from the corresponding neutral azide ion adducts (gem-diazides), were calculated from the experimental values of k(az)/k(s) (M(-1)) and k(solv) (s(-1)) for solvolysis of the gem-diazides, respectively, using k(az) = 5 x 10(9) M(-1) s(-1) for the diffusion-limited reaction of azide ion with alpha-substituted benzyl carbocations.