Co-host: The Chemical Society of Japan, The Society of Synthetic Organic Chemistry, Japan (Cooperation)
The gas-phase basicities (GBs) for a representative set of six formamidine ureas with variations in the imino substitutent (RN=CHN(Me)CONHMe) were determined in proton-transfer equilibria by ion cyclotron resonance (ICR) mass spectrometry and further explored with calculations at the B3LYP/6-31+G* level of theory. Relative GBs were linearly correlated to the inductive effect of the imine nitrogen substituents, giving a rohI= -33. The magnitude of the rohI value suggests that protonation occurs preferentially at the imino nitrogen. The calculated basicities for the imino N-protonated ones are in good agreement with the observed values. The GB values were also found to be similar to those previously reported for N1,N1-dimethyl-N2-substituted formamidines. These results indicate importance of intramolecular hydrogen-bonding interaction with the amide oxygen in the protonated ion.
