1H NMR and 13C NMR spectral data are presented for 1,2-dimethoxybenzene-α,α′-13C, as well as for a number of other anisole derivatives. For the title molecule, the coupling constants between the 13C nucleus in the side chain and the para ring proton or 13C nucleus in the benzene ring show that the expectation value of sin2 θ is very near 0.2 at 300 K, where θ is the angle by which the methoxy groups twist out of the aromatic plane. This value of [Formula: see text] is much larger than that of 0.05 for anisole in solution, emphasizing the greater conformational mobility of the methoxy groups in 1,2-dimethoxybenzene (DMB). Long-range coupling constants between the methyl and ring protons in DMB are also discussed and compared with those in anisole and some of its derivatives. The preponderance of conformations with large values of θ, thought to occur in the vapor, disappears in solution at ambient temperatures. Under these conditions, the molecule is perhaps best described as preferring a planar conformation in which, however, the methoxy groups undergo excursions in θ whose average value is near 25°. Keywords: 1,2-dimethoxybenzene, conformational behaviour, internal mobility, long-range coupling constants, 1H and 13C NMR.

Unlike their counterparts in anisole or toluene derivatives, the six-bond spin–spin coupling constants between para ring protons or 19F nuclei and protons or 13C nuclei in the sidechain of derivatives of benzaldehyde, acetophenone, and benzophenone can apparently contain components of opposite sign, at least for the fluorine derivatives. The σ–π components are much smaller in magnitude than in toluene derivatives, leading to very small or unobservable coupling constants. Consequently they are of limited use in conformational analysis. INDO MO FPT computations and their modifications are examined as to the reasons for the small σ–π magnitudes. Although the spin polarizability of the 2pz orbital on oxygen appears to play an important role in the transmission of nuclear spin state information, the computations do not account for a 19F coupling mechanism that appears to be significant for planar conformations. On the other hand, spin–spin coupling constants over five formal bonds to meta protons are sizeable and stereospecific.

AbstractIn 2‐trifluoromethylphenyldifluorophosphine the proximate couplings 4J(19F31P) and 5J(19F19F) are + 68.3 and + 8.3 Hz, respectively. 1J(13C31P) is −57.0 Hz, 2J(13C‐1, 10F) is + 9.9 Hz and 2J(13C‐6, 13C‐6, 31P) is + 10.1 Hz. The trifluoromethyl substituent induces substantial changes in some coupling constants, particularly those between the 31P and ring 13C nuclei.

The reaction of an alkyl chloroformate with dimethyl sulfoxide gives the corresponding alkoxysulfonium chloride (I; X = 0) and carbon dioxide. However, the corresponding reactions with chlorothiolformate esters do not yield the salts (I; X = S). Phenyl chlorothiolformate reacts with dimethyl sulfoxide according to equation [1].