Spin-spin coupling between side-chain and ring protons and the effect of electron delocalization on allylic coupling

Abstract

The side-chain-ring coupling constants3 in the three isomeric tetrachlorotoluenes are Jortho 0.63�0.02 c/s, Jmeta 0.36�0.02 c/s, and Jpara 0.63�0.01 c/s. The magnitudes of side-chain coupling constants in benzene derivatives are discussed. In symmetrical six-membered aromatic and heterocyclic compounds the magnitude of the ortho side-chain coupling constants is approximately 0.6 c/s but varies from less than 0.3 cis to 1.1 c/s in molecules where some bond localization occurs. Ortho side-chain coupling constants in five-membered heterocyclic compounds also appear to be affected by electron localization. It is therefore likely that the magnitude of the ortho side-chain coupling constants may be a direct measure of bond order. Long-range coupling data on indole derivatives are reported. In two β,β-dimethylstyrenes the stronger side-chain to ring coupling is to the ortho position. The relation between allylic coupling and electron delocalization is explored and a new criterion for electron delocalization proposed.

The preferred conformations in solution and rotational barriers of the phenyl moiety in 3,5-dichlorobenzyl derivatives of ammonia, dimethylamine, and dimethylarsine

“…Because the phenyl proton region in benzyl compounds is too complex for a precise analysis of its 'H nmr spectrum, the compounds contained chlorine substituents at the meta positions. There is no evidence that these substituents alter the conclusions to be arrived at below (6,8).…”

“…On the other hand, when X = C1, Br, or I the J method indicates that 3 is preferred by 2 kcall mol or more (2). The long-range spin-spin coupling c o n~t a n t ,~~,~~~~~, between the methylene protons and the ring proton in the para position obeys a sin2 8 relationship, where 8 is the angle by which the C-H bond on the side chain is twisted out of the plane of the benzene ring (3)(4)(5)(6).…”

Influence of Lewis acids on the Diels–Alder reaction. II. Rearrangement of 1- and 1,4-substituted diethyl 7-oxabicyclo[2•2•1]2,5-heptadiene-2,3-dicarboxylate adducts to 4- and 4,6-substituted diethyl 3-hydroxyphthalates

“…Each compound gave a characteristic AB pattern for two ortho coupled aromatic hydrogens. In two compounds, the proton giving rise to the low-field half of the AB pattern was long-range coupled (21) to the benzylic methyl (2b) or methylene (3) hydrogens, while in all three, the proton giving rise to the high-field part of the AB system had a chemical shift consistent with the presence of an ortho phenolic hydroxyl group (22 a carbonyl function would give a signal at lower field (ca. z 2.0) (22).…”

Spin–spin coupling constants between side-chain and ring fluorine nuclei in some benzotrifluoride, benzal fluoride, and benzyl fluoride derivatives: coupling mechanisms

“…and J? : , ?, in toluene derivatives have been discussed in some detail (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12). In addition to their intrinsic interest as indicators of electronic structure, some of these couplings are useful in the aetermination of conformational preferences and, indeed, of internal barriers to rotation in benzene derivatives (13)(14)(15)(16).…”