Gas-phase enthalpies of formation of the fluorobenzenes family and their dewar isomers from ab initio calculations

The standard gas-phase enthalpies of formation, at T= 298.15 K, of the complete series of fluorobenzene and their corresponding dewar isomers have been determined by means of the CBS-QB3 and G3MP2B3 composite approaches. These values have been estimated by using appropriate supporting reactions, such as, reactions of atomization or of atom substitution. The results show that there is a linear dependence between the enthalpy of the most stable n-fluorobenzene and the corresponding n-fluorodewar benzene (n = 0, 1,...,6). Further, the estimates are always more negative than the experimental results and so, suggested enthalpies of formation for 1,2,3-, 1,2,4- and 1,3,5-trifluorobenzenes and for 1,2,3,4- and 1,2,3,5-tetrafluorobenzeiies are those retrieved from G3MP2B3 calculations added by 8 kJ/mol. The interaction of four different M+ ions with fluorobenzene and the three difluorobenzenes shows that the a-interaction with 1,2-difluorobenzene is stronger than pi-interaction on these fluorobenzenes. (c) 2006 Elsevier B.V. All rights reserved.