Dissociation of ionized benzophenones investigated by the kinetic method: effective temperature, steric effects and gas‐phase CO^+• affinities of phenyl radicals

Abstract

Ionized benzophenones ([PhC(O)PhY](+*); Y = 4 - NO(2), 4 - CF(3), 4-F, 4-Br, 4-Me, 3,4-diMe, 4-OH, 4-OMe, 2-Cl, 2-Me, 2-OH, 2,6-diMe) undergo competitive dissociation upon collision-induced dissociation (CID) at 20 eV collision energy to generate benzoyl cations ([PhCO](+) and [YPhCO](+)) and phenyl radicals (Ph(*) and YPh(*)). For the para-substituted benzophenones, the natural logarithm of the abundance ratio of the benzoyl cations [ln([PhCO(+)]/[YPhCO(+)])] is found to correlate linearly with the calculated CO(+*) affinities of the phenyl radicals Ph(*) and YPh(*). A deviation from linearity is observed for the ortho-substituted isomers. This is probably due to a significant intramolecular steric interaction between the carbonyl group and the ortho substituent which prevents the formation of a stable planar system. An observed shift in the intercept relative to the origin is interpreted as the result of a systematic error in the calculated CO(+*) affinities and this effect is minimized by calculations at a higher level. The dissociation of ionized para-substituted benzophenones is associated with a relatively high effective temperature of 1816 +/- 41 K, calculated from the slope of the kinetic method plot, a value that is consistent with a covalent bond in the activated ion. In addition, Delta(DeltaS(CO(+) )), the dissociation entropy of the benzoyl cations to form CO(+*) and the aryl radical, is found to be about 4 J mol(-1) K(-1) by employing the extended version of the kinetic method.

Comparative Study of Mono- and Dinuclear Complexes of Late 3d-Metal Chlorides withN,N-Dimethylformamide in the Gas phase

“…Thus, [(DMF) 2 Zn 2 Cl 3 ] + with m / z 379 has a slightly smaller arrival time than [(DMF) 3 ZnCl] + with m / z 318. Interestingly, the arrival time distribution of mass-selected [(DMF) 2 Zn 2 Cl 3 ] + ( m / z 378.781) shows a small second component at t a = (4.06 ± 0.06) ms in addition to the major component with t a = (4.45 ± 0.06) ms; modeling with Gaussian functions suggest an about 1:30 ratio of the two components. , Observation of a minor isomer with lower mobility is fully consistent with the structures predicted for [(DMF) 2 Zn 2 Cl 3 ] + (Figure ). The major component is assigned to structure 6 , [(DMF) 2 Zn(μ-Cl) 2 ZnCl] + , a contact ion pair with a significant dipole moment (μ calc = 13.1 D), which promotes the interaction with the gas present in the mobility unit.…”

On-line chiral analysis using the kinetic method

“…For example, proton affinities have been studied by mass selecting proton-bound dimers and measuring the relative rates of their competitive dissociations. 3 This methodology has also been used to probe affinities (ion and electron), [4][5][6][7][8][9][10][11] ionization energies, 12,13 acidities, [14][15][16][17][18][19][20] steric effects, 21,22 isotope effects [22][23][24] and entropy changes. [25][26][27] Reviews of the capabilities and theoretical basis of the kinetic method have appeared.…”

Special Issue with Research Topics on “Recent Analysis and Applications of Mass Spectra on Biochemistry”

“…The kinetic method developed by Cooks and co-workers shows many advantages, among others [69]. In addition, a linear correlation between the energetics of MS reactions based on Hammett free energy and kinetic parameters has been established by McLafferty and co-workers [70]. Data on the intensity of peaks of the mass spectra of parent and product ions of analytes examining reaction kinetics show a linear relation between intensity peak ratio and time of chemical reaction (r 2 = 0.99) [64][65][66][67][68].…”