Ž . Chemical Physics 241 1999 167–177 Computational studies in aqueous and chloroform solutions of complex organic solutes: distinctive effects of the solvent on solutes with small chemical differences Elaine A. Armelin a , Carlos Aleman b, ) , Paulo M. Donate a , Sergio E. Galembeck a ´ a Departamento de Quımica da Faculdade de Filosofia, Ciencias e Letras de Ribeirao Preto, UniÕersidade de Sao Paulo, AÕenida ´ ˆ ˜ ˜ Bandeirantes No. 3900, 14049-901, Ribeirao Preto, SP, Brazil ˜ b Departament d’Enginyeria Quımica, E.T.S. d’Enginyers Industrials de Barcelona, UniÕersitat Politecnica de Catalunya, Diagonal 647, ´ ` Barcelona E-08028, Spain Received 6 April 1998; in final form 24 September 1998 Abstract The solvation in chloroform and aqueous solutions of three complex organic molecules have been investigated using Ž . self-consistent reaction-field SCRF methods. Solutes contain a phenyl ring with two attached methoxy groups, differing only in the chemical nature of the two functional groups located at the end of a flexible aliphatic chain. The study of solutes with only such small difference constitute a challenge for SCRF methods. Calculations in solution were performed on a selected number of conformers generated through a conformational search. The results provide a picture of the changes induced by the different solvents on the conformational preferences of the solutes. Conformations are described using general structural patterns rather than discrete structures due to the flexibility of the methoxy groups and the aliphatic chain. On the other hand, solute–solvent interactions have been analyzed and related with the transfer free energies and the partition coefficients to chloroform from water. q 1999 Elsevier Science B.V. All rights reserved. 1. Introduction The ability to understand the solvation of organic solutes in different solvents is very important in chemistry. Thus, solvation is useful for the predic- w x tion of the chemical reactivity 1–3 , the determina- w x tion of transfer free energies between solvents 4–6 and the conformational analysis in condensed phases w x 7–10 . Much progress has been made in the past few years on the development of quantum self-con- Ž . sistent reaction-field SCRF methods for describing ) Corresponding author. Fax: q34-93401-6600r7150. w x the effects of both aqueous 1,11–23 and organic w x solvents 24–27 . wx In a recent work 6 we compared the free ener- Ž . gies of solvation DG in aqueous and organic sol solutions for simple solutes with amide, keto and ester functional groups, i.e. CH –X–CH and CH – 3 3 3 X–CH –CH –X–CH with X s NHCO, C5O and 2 2 3 COO. Results indicate that the solvation of the amide derivatives increases with the polarity of the solvent whereas for the keto and ester derivatives the solva- tion in organic solvents is favored over water. More recently, the effects of the aqueous solvent on pep- tides with amide and retro-amide groups were ana- w x lyzed 28 . Results indicated that solute–solvent in- 0301-0104r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0301-0104 98 00410-8