New thermochemical parameter for describing solvent effects on IR stretching vibration frequencies - Communication 2. Assessment of cooperativity effects

Solvent effects on O-H stretching vibration frequency of methanol in hydrogen bond complexes with different bases, CH3OH center dot center dot center dot B, have been investigated by FTIR spectroscopy. Using chloroform as a solvent results in strengthening of CH3OH center dot center dot center dot B hydrogen bonding due to cooperativity between CH3OH center dot center dot center dot B and Cl3CH center dot center dot center dot CH3OH bonds. A method is proposed for quantifying the hydrogen bond cooperativity effect. The determined cooperativity factors take into account all specific interactions of the solute in proton-donor solvents. In addition, a method of estimation of cooperativity factors A(b) and A(OX) in system (CH3OH)(2)center dot center dot center dot B is proposed. It is demonstrated that in such systems, the cooperativity factor of the OH center dot center dot center dot B bond decreases and that of the OH center dot center dot center dot O bond increases with increasing the acceptor strength of the base B. The obtained results are in a good agreement with the data obtained previously from matrix-isolation FTIR spectroscopy. (c) 2005 Elsevier B.V. All rights reserved.