Substituent effects on the blue-shifting hydrogen bonds between X - C ≡ C - CF₂ - H and water

MP2/6-31 + g(d) calculations were performed verifying the existences of blue-shifting X - C ≡ C - CF₂ - H⋯OH₂ hydrogen bonds. Detailed analyses revealed that the interaction energy and donor-acceptor distance had good correlations with the substituent Hammett constants. However, the extent of C-H bond contraction and the blue shift of the C-H stretching vibration did not show any good correlation with the traditional substituent constants, indicating that certain more complicated mechanisms might be involved in the present systems. Nevertheless, it was found that highly electron-withdrawing susbtituents were not favorable to the C-H bond contraction, and it was suggested that the attractive interaction between water and the carbon of - CF₂H probably played an important role in the blue shift.