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235 Probing the Reactive Center for Site Selective Protonation in a Molecule by the Local Density Functional Descriptors Sandip K. Rajak University of Kalyani, India Nazmul Islam University of Kalyani, India Dulal C. Ghosh University of Kalyani, India Chapter 9 ABSTRACT In this study, the authors have explored the efficacy of the local density functional descriptors like the fukui functions (f), the local softness (s) and the local philicity as probe for the reactive centers and site selectivity of the chemico-physical process of protonation of some molecules having multiple site for protonation, viz CH 3 NCO (Methyl isocyanate), CH 3 NCS (methyl isothiocyanate), NH 2 OH (hydroxyl amine), NH 2 OCH 3 (o-methylhydroxylamine) , CH 3 NHOH (N-methylhydroxylamine), NH 2 CH 2 COOH (glycine), CH 3 CH(NH 2 )COOH (alanine) and OHCH 2 CH 2 NH 2 (ethanol amine) . The authors have seen in terms of the numerical values of the local descriptors measures the reactivity (nucleophilicity) of a particular atomic site of a donor center towards a proton. In all cases, it can be said that the dynamic chemico-physical process of site selectivity can nicely be correlated in terms of the computed values of the local descriptors. Thus, it is found that the theoretical descriptors of the DFT can be efficiently exploited to study the mechanism of site selectivity in a chemical reaction. DOI: 10.4018/978-1-4666-1607-3.ch009 Copyright © 2012, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited.