Exceptional proton affinities of push–pull nitriles substituted by the guanidino and phosphazeno groups

Abstract

Effects of the pushing groups (electron donors) for nitriles increase as follows: H₂N < H₂N–NN < H₂N–CHCH < H₂N–CHN < (H₂N)₂CCH < (H₂N)₂CN < (H₂N)₃PN. The G2(MP2)-calculated PA(N-cyano) for (H₂N)₂CN–CN and (H₂N)₃PN–CN are larger than that of HCN by 186 and 250 kJ mol⁻¹, respectively. The hypothesis of protonation in the gas phase at the N-imino and N-amino atoms, corresponding respectively to PAs weaker by 30 and 70 kJ mol⁻¹ than that of the N-cyano site, can be rejected.