CARBON-OXYGEN BOND STRENGTH IN DIPHENYL ETHER AND PHENYL VINYL ETHER - AN EXPERIMENTAL AND COMPUTATIONAL STUDY

The thermal decomposition of gaseous diphenyl ether (DPE) and phenyl v inyl ether (PVE) has been studied, at atmospheric pressure in hydrogen and in a very low-pressure reactor, over a temperature range of 1050- 1200 K. The high-pressure rate constant for homolytic bond cleavage C6 H5O-C6H5 --> C6H5O. + C6H5. (1) obeys k(1) (s(-1)) = 10(15.50) exp(-75 .7/RT). Two pathways can be distinguished for C6H5OC2H3: C6H5. + C2H3O . (2) and C6H5O. + C2H3. (3) The overall rate constant follows k(2+3) (s(-1)) = 10(15.50) exp(-73.3/RT). The rate ratio, upsilon(2)/upsilon( 3), amounts to 1.8 and appears to be temperature independent. These fi ndings result in bond dissociation energies (BDE) at 298 K for C6H5O-C 6H5, C6H5-OC2H3, and C6H5O-C2H3 of 78.8, 75.9, and 76.0 kcal mol(-1), respectively. The enthalpies for reactions 1-3 have been also determin ed at 298 and 1130 K by ab-initio calculations using the density funct ional theory formalism on the B3LYP/6-31G(d) and B3LYP/6-311++G(d,p) l evel. Comparison between experiments and theoretical calculations reve als distinct variances (ca. 3-4 kcal mol(-1)) for the BDE(C-O) in aryl ethers and the BDE(O-H) in phenol and vinyl alcohol but a close agree ment for the BDE(C-H) in the related hydrocarbons: toluene, benzene, a nd ethene.