Determination of the electron affinities of α- and β-naphthyl radicals using the kinetic method with full entropy analysis. The C — H bond dissociation energies of naphthalene

✍ Scribed by Harvey A. Lardin; Robert R. Squires; Paul G. Wenthold

• Publisher: John Wiley and Sons
• Year: 2001
• Tongue: English
• Weight: 213 KB
• Volume: 36
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/jms.159

✦ Synopsis

Abstract

The C — H bond dissociation energies for naphthalene were determined using a negative ion thermochemical cycle involving the gas‐phase acidity (Δ__H__~acid~) and electron affinity (EA) for both the α‐ and β‐positions. The gas‐phase acidity of the naphthalene α‐ and β‐positions and the EAs of the α‐ and β‐naphthyl radicals were measured in the gas phase in a flowing afterglow–triple quadrupole apparatus. A variation of the Cooks kinetic method was used to measure the __EA__s of the naphthyl radicals by collision‐induced dissociation of the corresponding α‐ and β‐naphthylsulfinate adducts formed by reactions in the flow tube portion of the instrument. Calibration references included both π and σ radicals, and full entropy analysis was performed over a series of calibration curves measured at collision energies ranging from 3.5 to 8 eV (center‐of‐mass). The measured __EA__s are 33.0 ± 1.4 and 31.4 ± 1.0 kcal mol^−1^ (1 kcal = 4.184 kJ) for the α‐ and β‐naphthyl radicals, respectively. The gas‐phase acidities for naphthalene were measured by the DePuy silane cleavage method, which utilizes the relative abundances of aryldimethylsiloxides and trimethylsiloxide that result from competitive cleavages from a proposed pentacoordinate hydroxysiliconate intermediate. The measured acidities are 394.0 ± 5.0 and 397.6 ± 4.8 kcal mol^−1^ for the α‐ and β‐ positions, respectively. The C — H bond dissociation energies calculated from the thermochemical cycle are 113.4 ± 5.2 and 115.4 ± 4.9 kcal mol^−1^ for the α‐ and β‐positions, respectively. These energies are, to within experimental error, indistinguishable and are approximately the same as the first bond dissociation energy for benzene. Copyright © 2001 John Wiley & Sons, Ltd.