THEORETICAL-STUDY OF CH-CENTER-DOT-CENTER-DOT-CENTER-DOT-O HYDROGEN-BONDS IN H2O-CH3F, H2O-CH2F2, AND H2O-CHF3

Ab initio methods have been used to study the CH ... O hydrogen bond b etween H2O and CH3F, CH2F2, and CHF3. The calculations have been carri ed out using the 6-31G*, 6-311G**, 6-311++G**, and 6-31G** basis sets at the MP2 and MP4 levels of theory. Interaction energies include bas is set superposition error adjustments. The results show that the stro ngest CH ... O hydrogen bond is the bisector one with the lone pairs o n the oxygen. The inclusion of each additional fluorine results in a s ystematic strengthening of the hydrogen bond by 1 kcal/mol as well as in the shortening of the hydrogen bond distance by 0.1 Angstrom.