FT-IR of unsaturated b-amino acids in different solvents systems P. Bruni, C. Conti, R. Galeazzi, E. Giorgini, G. Tosi * Dipartimento di Scienze dei Materiali e dellaTterra, Universita degli studi di Ancona, Via Brecce Bianche, I-60131 Ancona, Italy Received 2 September 2002; accepted 26 September 2002 Abstract The infrared study of the solvent effect on 2-methylen-3-phenyl-3-aminocarbonyl compounds, precursors of g-hydroxy- b-amino acids, is reported. Intramolecular hydrogen bonding between NH and ester carbonyl group is present in apolar solvents, while in polar or/and protic solvents specific solute – solvent interactions are pre-dominant. In mixtures of chloroform and cyclohexane, various equilibria are present; the composition of the solute – solvent different complexes differs as the mol% of the solvent system changes. Conformational analysis confirms the infrared findings. q 2003 Elsevier Science B.V. All rights reserved. Keywords: Solvent effect; Infrared spectra; Hydrogen bonding 1. Introduction 2-Methylen-3-phenyl-3-aminocarbonyl com- pounds are interesting derivatives to be inserted into oligopeptides moieties to induce conformation- al constrictions. In addition, they can be considered precursors of g-hydroxy-b-amino acids. In these compounds, the presence of a diversified function- ality, such as carbonyl (ester and amide) and amino groups, that can undergo inter- or intramolecular hydrogen bonding, makes them interesting for a FT-IR study. Recently, infrared spectroscopy has been used to investigate solute – solvent inter- actions; in particular, in order to understand the influence of various solvent parameters, vibrational analysis was applied to study keto, ester and hydroxy groups [1–3]. In this work, a FT-IR study on 2-methylen-3-phenyl-3-aminocarboxylates 1 – 3 in neat phase and in solution of different solvents (pure and in mixture) is reported: intra- and intermolecular interactions are evaluated; on compounds 1 and 2 results from conformational analysis have been compared with IR data. 2. Experimental Compounds 1 – 3 were synthesised according to the procedure in Ref. [4]. Infrared spectra were obtained with a Perkin–Elmer Spectrum GX FT-IR spectrometer; treatment of the data was achieved with a Galactic software package Grams/32. All solvents were Aldrich spectroscopic grade. 0022-2860/03/$ - see front matter q 2003 Elsevier Science B.V. All rights reserved. PII: S0022-2860(02)00634-8 Journal of Molecular Structure 651–653 (2003) 245–252 www.elsevier.com/locate/molstruc * Corresponding author. Tel.: þ39-071-220-4723; fax: þ 39-071- 220-4714. E-mail address: tosi@mta01.unian.it (G. Tosi).