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

Abstract

The C - H bond dissociation energies for naphthalene were determined using a negative ion thermochemical cycle involving the gas-phase acidity (Delta H (acid)) and electron affinity (EA) for both the alpha- and beta-positions. The gas-phase acidity of the naphthalene alpha- and beta-positions and the EAs of the alpha- and beta-naphthyl radicals were measured in the gas phase in a flowing after glow-triple quadrupole apparatus. A variation of the Cooks kinetic method was used to measure the EAs of the naphthyl radicals by collision-induced dissociation of the corresponding alpha- and beta-naphthylsulfinate adducts formed by reactions in the flow tube portion of the instrument. Calibration references included both pi and sigma 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 EAs are 33.0 +/- 1.4 and 31.4 +/- 1.0 kcal mol(-1) (1 kcal = 4.184 kJ) for the alpha- and beta-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 penta coordinate hydroxysiliconate intermediate. The measured acidities are 394.0 +/- 5.0 and 397.6 +/- 4.8 kcal mol(-1) for the alpha- and beta- 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 alpha- and beta-positions, respectively. These energies are, to within experimental error, indistinguishable and are approximately the same as the first bond dissociation energy for benzene.

Microcanonical analysis of the kinetic method. The meaning of the “apparent entropy”

“…Researchers using the full entropy analysis method have equated the apparent entropy term either with the entropy difference for dissociation, ⌬⌬S(T), [21][22][23][24], or with the entropy difference for activation, ⌬⌬S ‡ (T) [26]. The assumption ⌬⌬S(T) ϭ ⌬⌬S ‡ (T) is also implicit in implementations of the kinetic method that calibrate against Gibbs energies instead of enthalpies, i.e., ln(I 2 /I 1 ) ϭ Ϫ⌬⌬G/RT eff instead of eq 7.…”

“…Armentrout proposed an improved statistical treatment of extended kinetic method data to obtain enthalpy differences and the apparent entropies with realistic uncertainties [21]. This "full entropy analysis" has been used for measurements of proton affinities and electron affinities [22][23][24][25][26] by the extended kinetic method. In their finite heat bath theory and RRKM theory simulations, Laskin and Futrell [9] found reasonable agreement between the apparent entropy and the thermodynamic entropy difference.…”

Vibrational and Electronic Structure of the α- and β-Naphthyl Radicals via Slow Photoelectron Velocity-Map Imaging

“…21,22 Experimental characterization is sparser. Reed and Kass 23 and Lardin et al 24 measured the electron affinities (EAs) of the α-and β-naphthyl radicals through kinetic methods and calculated the α and β C−H bond dissociation energies of naphthalene. Both studies found the α anion to be lower in energy than the β anion by several kJ/mol, favoring α formation in deprotonation of naphthalene.…”

“…Our overview spectrum of the α-naphthyl X̃band ( Figure S2) is in excellent agreement with the naphthyl spectrum reported by Ervin et al 18 Our measured EAs for α-and β-naphthyl (Table 1) agree with prior work, with much improved precision. 18,23,24 Both X̃bands show extensive FC activity, indicative of a large change in geometry upon photodetachment. For these transitions, the electron is detached from an s-p hybrid orbital localized on the deprotonated site; calculated Dyson orbitals are shown in Figure 3.…”

Investigation of Aromaticity of Tri and Tetraazanaphthalene Derivatives

“…Naphthalene is composed of two fused benzenes, and it has been studied frequently with its derivatives for about fifty years, since 1968 (Yencha & El-Sayed, 1968;Kitagawa, 1968;Kaim, Tesmann & Bock, 1980;Klasinc, Kovac & Gusten, 1983;Meylan & Howard, 1991;Heinis, Chowdhury & Kebarle, 1993;Schiedt, Knott, Barbu, Schlag & Weinkauf, 2000;Lardin, Squires & Wenthold, 2001;Song, et al 2002). Ghiasi (Ghiasi, 2005) worked on the aromaticity of mono-and di-silanaphthalene after the first achievement of the synthesis of 1-Silanaphthalene was published by Takeda et al (Takeda, Shinohara & Tokitoh, 2002).…”