Application of the electro-optic Kerr effect to investigation of the intermolecular H-bond  O.V. Prezhdo a , V.V. Prezhdo b, * a Department of Chemistry, University of Washington, Seattle, WA 98195-1700, USA b Institute of Chemistry, Pedagogical University, 5 Checinska Street, 25-020 Kielce, Poland Received 25 October 1999; received in revised form 25 January 2000; accepted 7 February 2000 Abstract The intermolecular H-bond plays an important role in chemical and biological systems and processes. This review considers various aspects of the application of the electro-optic Kerr effect in the investigation of the intermolecular H-bond. Current approaches to the determination of structures of H-bonded molecular complexes are described. From the measurements of the electro-optic and molar Kerr constants of the complexes and their individual components these methods produce the basic parameters of the H-bonded complexes, including the complex formation equilibrium constant (K) and the H-bond dipole moment (m H ). The importance of a new parameter, namely, the structural additive difference of the molar Kerr constants (DmK) S is illustrated. The prospects of future progress in the studies of the intermolecular H-bond by the electro-optic methods are discussed.  2000 Elsevier Science B.V. All rights reserved. Keywords: H-bond; Electro-optic Kerr constant; Dipole moment; Proton acceptor ability; Equilibrium constant; Structure of complexes 1. Introduction Currently, there exist much data dealing with acid– base interactions. Reviews can be found in mono- graphs edited by Gragerov et al. [1], Schuster et al. [2], Sokolov [3], Ratajczak and Orville-Thomas [4], Huyskens et al. [5] and Dore and Teixeira [6]. A general interaction scheme between an acid A–H and a base B is expressed as A–H + B I , A–H … B II , A - … HB + III , A - … S … HB + IV , A - + HB + V 1 Here, step I describes the non-interacting compo- nents; step II represents formation of the intermole- cular H-bond; step III shows the ionic pair complex; step IV leads to the solvent-separated ion pair; finally, step V represents dissociation of the ion pair and formation of the separate ions. Investigation of the electro-optic properties consti- tutes an important approach to the determination of the geometric structures of molecules and complexes, including complexes with the intermolecular H-bond [7]. The utility of the electro-optic measurements is Journal of Molecular Structure 526 (2000) 115–130 0022-2860/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S0022-2860(00)00446-4 www.elsevier.nl/locate/molstruc  Presented at the XIV International School-Seminar “Spectro- scopy of Molecules and Crystals”, Odessa, Ukraine, 7–12 June 1999. * Corresponding author. Tel.: + 48-81-361-4012; fax: + 48-81- 361-4942. E-mail address: victor@top.pu.kielce.pl (V.V. Prezhdo).