An estimate of the spin–spin coupling constant, ¹J(¹H,¹³C), in gaseous benzene

Abstract

An excellent linear correlation (r = 0.9999) exists between the spin-spin coupling constants

Solvent Effects on the Indirect Spin–Spin Coupling Constants of Benzene: The DFT-PCM Approach

“…(2) Our calculations slightly underestimate the solvent shift in CS 2 relative to cyclohexane, whereas we overestimate the effects for pyridine and acetone. However, this is consistent with our model, in which we consider an infinitely diluted benzene molecule in a pure solvent, whereas a more reasonable representation would be a 5% solution of benzene in solvent [43]. This could be modeled using an "effective" dielectric constant [43,45], which would lead to an increase of the dielectric constant of the cyclohexane solution and reduce the effective dielectric constants of the other solutions, thus probably leading to a better agreement with the experimental observations.…”

“…Our results corroborate the observation [23,42] that the MCSCF results significantly overestimate most of the coupling constants. In a recent paper, an attempt was made to extract a vibrationally averaged 1 J(H 13 C) coupling constant for benzene in the gas phase by extrapolation of accurately measured coupling constants in four relatively non-polar solvents to a dielectric medium with a dielectric constant of 1 (which corresponds to the dielectric constant of vacuum) [43]. In addition to depend strongly on the solvent being well represented as a structureless dielectric continuum, such an approach also relies heavily on the assumption that the spin-spin coupling constant varies smoothly with the dielectric constant.…”

“…We have reinvestigated this extrapolation scheme by PCM calculations using the same solvents as in Ref. [43]. Our results for 1 J(H 13 C) are collected in Table 2.…”

“…If we try to apply the linear extrapolation done in Ref. [43] to our theoretical data, we get a predicted gas-to-cyclohexane solvent shift of 0.869 Hz and 1.112 Hz for the coupling constants calculated at the vacuum geometry and the solvent-relaxed geometry, respectively. Both of these numbers are almost twice as large as the calculated solvent shift, clearly illustrating the inadequacy of the linear regression for obtaining the gas-phase value of the spin-spin coupling constant.…”

37,35Cl isotope effects on19F and13C chemical shifts of chlorofluoro- and hydrochlorofluorocarbons

“…Except in the simplest of cases, this is not a trivial task. These materials are often encountered in complex mixtures, and even pure materials may yield non-first-order 19 F and 1 H spectra that cannot be interpreted by inspection alone. In the simplest cases, the spectroscopist's common tools (e.g.…”