Carbon−Oxygen Bond Strength in Diphenyl Ether and Phenyl Vinyl Ether:  An Experimental and Computational Study

Abstract

The thermal decomposition of gaseous diphenyl ether (DPE) and phenyl vinyl 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 C6H5O−C6H5 → C6H5O• + C6H5 • (1) obeys k 1 (s-1) = 1015.50 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) = 1015.50 exp(−73.3/RT). The rate ratio, v 2/v 3, amounts to 1.8 and appears to be temperature independent. These findings result in bond dissociation energies (BDE) at 298 K for C6H5O−C6H5, 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 determined at 298 and 1130 K by ab-initio calculations using the density functional theory formalism on the B3LYP/6-31G(d) and B3LYP/6-311++G(d,p) level. Comparison between experiments and theoretical calculations reveals 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 agreement for the BDE(C−H) in the related hydrocarbons: toluene, benzene, and ethene.

Computational Study of Bond Dissociation Enthalpies for Substituted β‐O‐4 Lignin Model Compounds

“…It is usual practice when calculating BDEs to include only the lowest energy conformer. [29,77,78] However, many of the conformers were appreciably populated at 298 K. Instead of excluding all but the lowest energy geometry, we calculated a weighted BDE by a Boltzmann distribution, approximated as e…”

A theoretical and mass spectrometry study of the fragmentation of mycosporine-like amino acids

“…The chemistry of ions in the gas-phase may be thought of as an ideal process since the ions can be considered to be isolated. In this context, the methodologies that are used to solve the Schrödinger equation (either ab initio or DFT) apply the condition of the absence of any intermolecular interactions [40][41][42][43].…”

Determination of Bond Dissociation Enthalpies in Solution by Photoacoustic Calorimetry

“…Despite their importance, BDEs in more complex species are more difficult to measure and thus less reliable. 7 Experimental approaches for the direct and indirect determination of BDEs in the gas phase 4,7 or in solution (electrochemical cycles 8 and PAC) as well as new computational methods such as density functional theory 9 have led to a dramatic increase in the number of reliable BDEs for organic and organometallic compounds. For consistency, all of the data are normally extrapolated to standard state conditions (i.e., 298 K in the gas phase).…”