ISSN: 2410-9649 Tijar et al / Chemistry International 2(4) (2016) 201-221 iscientic.org. 201 www.bosaljournals/chemint/ editorci@bosaljournals.com Article type: Research article Article history: Received October 2015 Accepted December 2015 October 2016 Issue Keywords: Genetic algorithm Benzoic acid Salicylic acid Phthalic acid Multi niche crowding In this paper we present a detailed conformational study of three aromatic systems constituting the basic units of humic acids namely benzoic acid, salicylic acid and phthalic acid. The genetic algorithm, based on the multi-niche crowding (MNC) method, coupled with the semi-empirical AM1 method is used to analyze the potential energy surface (PES) of these systems. This algorithm, implemented in the MOPAC program and piloted by scripts, provides better detection of global and local minima in a reasonable time. The results obtained are comparable with those of previous studies. Three factors can be cited to justify the stability of conformations i.e. effects of conjugation, steric interactions and intramolecular hydrogen bonds. © 2016 International Scientific Organization: All rights reserved. Capsule Summary: The genetic algorithm based on the MNC method is used with the semi-empirical method AM1 in order to scan the potential energy surfaces of benzoic acid, salicylic acid and phthalic acid. Three factors can be cited to justify the stability of conformations i.e., effects of conjugation, steric interactions and intramolecular hydrogen bonds. Cite This Article As: R. Tijar, B. El Merbouh, M. Bourjila, A. EL Guerdaoui, R. Drissi El Bouzaidi, A. El Gridani and M. EL Mouhtadi. 2016. Conformational space analysis of neutral and deprotonated forms of benzoic acid, salicylic acid and phthalic acid using a genetic algorithm. Chemistry International 2(4) 201-221 INTRODUCTION Humic acids are the major components of the most common natural organic matter in the soil and in fresh water and water Sea (Witwicki and Jezierska, 2012). These naturally occurring acids play a major ecological and geochemical role. Their molecular structure is very complex and poorly defined which makes their full structural characterization extremely difficult. Many efforts have been made and many available techniques and methods have been used to derive an average structure of these acides (Susan et al., 1996; Yu-hui and Ting, 1997; Mamadou et al., 2003). Previously, they have been described as macromolecular polymers containing various functional groups such as carboxylic, phenolic, hydroxyl and carbonyl. Recently, based on experimental data, it has been suggested that such materials are likely rather supramolecular forming into smaller molecular units interacting by non-covalent forces such as van der Waals forces and hydrogen bonds (Markus et al., 2004; Tossell, 2009). These Chemistry International 2(4) (2016) 201-221 Conformational space analysis of neutral and deprotonated forms of benzoic acid, salicylic acid and phthalic acid using a genetic algorithm R. Tijar 1 , B. El Merbouh 1 , M. Bourjila 1 , A. EL Guerdaoui 1 , R. Drissi El Bouzaidi 1,2,* , A. El Gridani 1 and M. EL Mouhtadi 1 1 Laboratoire de chimie physique, Faculté des Sciences, B.P. 8106, Université Ibn Zohr, 80000, Agadir, Maroc. 2 Centre Régional des Métiers de L’Education et de la Formation (CRMEF), Souss Massa Daraa, Inezgane, Maroc. *Corresponding author’s E. mail: drissi.rachid1@hotmail.fr , Tel.: 212672222253, Fax: 212524882123 ARTICLE INFO A B S T R A C T