名称:
The Gas-Phase Acidity of HCP, CH3CP, HCAs, and CH3CAs: An Unexpected Enhanced Acidity of the Methyl Group
摘要:
The gas-phase acidities of methylidynephosphine, HC=P. ethylidynephosphine. CH3C=P. and ethylidynearsine, CH3C=As, have been measured by means of Fourier Transform Ion Cyclotron Resonance (FTICR) mass spectrometry and calculated Lit the CCSD(T)/6-311+G(3df,2p)//QCISD/ 6-311 + G(df.p) level of theory. An analysis of these results shows that, in contrast to the well-known fact that HC=N is a stronger acid than CH3C=N, CH3C=P and CH3C=As are more acidic than HC=P and HC=As, respectively. The most important consequence of this unexpected effect is that while HC=P and HC=As are found to be weaker acids than HC=N. the opposite trend is found for the corresponding methyl derivatives, the acidity of which increases as CH3C=N < CH3C=P < CH3C=As. Also the effects of deprotonation on the structures and the vibrational frequencies of HC=X and CH3C=X (X=N, P, As) compounds are qualitatively similar. but quantitatively very different for nitrogen- as compared with phosphorus- and arsenic-containing compounds. A rationalization of these differences in terms of the bonding differences is presented.