C-C Bond Cleavage in Aromatic Molecules : Benzene , Toluene and Naphthalene

Abstract

The calculated energy reaction path, for the C-C bond cleavage in benzene, applying the Density Functional Theory method, yielded the values for the activation energy, Ea= 221.561kcal/mol and reaction energy, Er= 146.938kcal/mol respectively. The corresponding values for the different bonds in toluene are; C1-C2, Ea= 200.640kcal/mol, Er =140.800 kcal/mol; C2-C3, Ea = 214.790kcal/mol, Er= 154.160kcal/mol; C3-C4, Ea= 209.560kcal/mol, Er= 174.110kcal/mol; C1-C7, Ea= 148.050kcal/mol, Er = 104.230kcal/mol. For naphthalene the calculated energy values were; C1-C2, Ea= 226.640kcal/mol, Er = 157.094kcal/mol; C2-C3, Ea= 255.677kcal/mol, Er= 205.147kcal/mol; C9-C10, Ea= 299.851kcal/mol, Er= 270.575kcal/mol. The geometries of all transition states were coplanar with (4n+2) electrons with the exception of toluene C2-C3 bond reaction where the C2 atom moves towards C6 to form a cyclopropene structure. The C2-C3 bond cleavage in naphthalene proceeds towards the splitting of two acetylene molecules from the mother molecule, beyond the transition state. The geometries of the aromatic transition states showed typical bond alternation distances i.e. classical C=C and C-C bonds.