The C-H ••• π bonds:: strength, identification, and hydrogen-bonded nature:: a theoretical study

Using the MP2 method and, in some cases, a basis set-up to aug-cc-pVTZ quality, the properties of C-H ... pi bonds have been investigated in model dimers. Their strength goes from 0.55 up to 2.5 kcal/mol, depending on the C-H carbon hybridization and the a system. The presence of these bonds is identified by the presence of a bond critical point linking the H atom and atoms of the a system. The critical point characteristics and the vibrational shift of the C-H ... pi bonded dimers are similar to those present in C-H ... O and O-H pi hydrogen-bonded dimers, thus indicating a hydrogen-bonded nature. (C) 2000 Elsevier Science B.V. All rights reserved.