Carbon‐13 NMR spectra of saturated heterocycles: XI—Tetrahydropyrans (oxanes)

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The 13C NMR spectra of 62 oxanes (tetrahydropyrans) with and without methyl substituents at various ring positions, some of them bearing in addition (or instead) ethyl, vinyl, ethynyl, carbomethoxy and methylol substituents at C‐2, have been recorded, and the 294 resulting chemical shifts have been correlated by multiple linear regression analysis. Axial and equatorial α‐, β‐, γ‐, δ‐, gem‐ and vic‐parameters for shifts caused by methyl groups at all ring positions, and similar parameters for Et,—CHCH2,—CCH, CO2Me and CH2OH groups at C‐2, are reported. Standard deviations of the parameters are, in most cases, within 0.3 ppm and the agreement of calculated and experimental shifts is excellent. This is probably the largest parameter set of this type extant. 13C NMR spectra of a number of additional substituted tetrahydropyrans, and of 3,6‐dihydro‐2H‐pyrans and 3,4‐dihydro‐2H‐pyrans, are tabulated and discussed.