EXPERIMENTAL (FT-ICR) VS CALCULATED (AM1) GAS-PHASE BASICITIES OF N1,N1-DIMETHYL-N2-PHENYLFORMAMIDINES - SUBSTITUENT AND SOLVENT EFFECTS

Gas-phase basicities (as GBs) for a series of 11 N1,N1-dimethyl-N2-phe nylformamidines are calculated by means of the semiempirical AM1 metho d and compared with those experimentally obtained from proton transfer equilibria measurements using FT-ICR mass spectrometry. Geometries of the neutral, N1-, N2- and X-protonated forms are discussed. AM1 calcu lations confirm the earlier conclusion based on experimental results t hat the N2 atom is the favoured site of protonation in the gas-phase. Its basicity is higher by ca. 25 kcal/mol than that of the N1 atom. Th e AM1 method reproduces satisfactorily the experimental gas-phase basi cities in the series under study. Calculated and measured GB of formam idines are linearly correlated to the substituent polarizability, fiel d and resonance effects. As compared to the aza group in pyridines the formamidine group is more sensitive to the transmission of the field, than the resonance effect. Sensitivity of the formamidine group to su bstituent effects is very close to that of the amino group in N,N-dime thylanilines. Substituent effects in the gas phase are compared with t hose found previously in solution.