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The C−H and α(C−X) Bond Dissociation Enthalpies of Toluene, C6H5-CH2X (X = F, Cl), and Their Substituted Derivatives: A DFT Study
journal contribution
posted on 2005-11-17, 00:00 authored by Pham-Cam Nam, Minh Tho Nguyen, Asit K. ChandraThe homolytic C−H bond dissociation enthalpies (BDEs) of toluene and its para- and meta-substituted
derivatives have been estimated by using the (RO)B3LYP/6-311++G(2df,2p)//(U)B3LYP/6-311G(d,p)
procedure. The performance of two other hybrid functionals of DFT, namely, B3PWP91 and O3LYP, has
also been evaluated using the same basis sets and molecules. Our computed results are compared with the
available experimental values and are found to be in good agreement. The (RO)B3LYP and (RO)O3LYP
procedures are found to produce reliable BDEs for the C−H bonds in toluene and the C−X (X = F, Cl) bond
in α-substituted toluene (C6H5−CH2X) and their substituted derivatives. The substituent effect on the BDE
values has been analyzed in terms of the ground-state effect and the radical effect. The effect of polarization
of the C−H bond on the substituent effect is also analyzed. The BDE(C−H) and BDE(C−X) values for
α-substituted (X = F and Cl) toluenes with a set of para substituents are presented for the first time.