Reactivity descriptors for the hydrogen bonding ability of aliphatic alcohols Maria Dimitrova, Sonia Ilieva, Boris Galabov * Department of Chemistry, University of Sofia, 1 James Bourchier Avenue, 1164 Sofia, Bulgaria Received 22 May 2003; revised 23 June 2003; accepted 24 June 2003 Abstract A series of 18 aliphatic alcohols and their hydrogen-bonded complexes with ammonia are studied by applying density functional theory computations at the B3LYP/631G(d,p) level. Theoretically determined electronic parameters—partial atomic charges and electrostatic potential at nuclei (EPN)—are employed to characterize the reactivity of the monomer alcohols. The variations of binding energy are also interpreted in terms of the well-known experimental solvatochromic parameters, a: It is shown that both the experimental a constants and EPN values characterize quantitatively the reactivity of the studied molecules toward the complexation process. A linear link between a constants and EPN values was also found. q 2003 Elsevier B.V. All rights reserved. Keywords: Hydrogen bonding descriptors; Complexes of alcohols and ammonia; Atomic charges; Electrostatic potential; Acidity constants 1. Introduction The aim of this study is to analyse the inter- dependences between several quantities that can be used to quantify the reactivity of molecules with respect the process of hydrogen bonding for a series of proton donor aliphatic alcohols. Ammonia is used as a model proton acceptor. The theme is of importance in the general characterization and understanding of weak intermolecular interactions as well as for applications in QSAR and QSPR analysis. QSAR and QSPR studies employ a number of different hydrogen bonding descriptors [1–9]. Important reac- tivity parameters are the solvatochromic hydrogen bond donor terms a and hydrogen bond acceptor terms b [1,7]. These quantities are derived exper- imentally from spectroscopic data. Atomic charges calculated according to different schemes are a natural choice in the search for theoretically derived descrip- tors. A combination of atomic charges and HOMO or LUMO energies has produced good results [10,11]. Minima and maxima in the molecular surface electrostatic potential have been shown also to predict satisfactorily the hydrogen bonding ability of a number of molecules [12,13]. Thermodynamic hydro- gen bonding parameters have been proposed by Raevsky et al. [14]. Dearden and Ghafourian have analysed the potential of a number of these descriptors in a study of a series of substituted anilines [15]. In a series of studies from this laboratory [16–20] it was shown that theoretically estimated electrostatic potential at nuclei (EPN) values correlate linearly 0022-2860/03/$ - see front matter q 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0022-2860(03)00417-4 Journal of Molecular Structure 657 (2003) 317–324 www.elsevier.com/locate/molstruc * Corresponding author. Tel.: þ 359-26256421; fax: þ 359- 29621913. E-mail address: galabov@chem.uni-sofia.bg (B. Galabov).