H-1-H-1 LONG-RANGE COUPLINGS IN FUSED CYCLOPROPANES - NMR SPECTRAL ASSIGNMENT AND CONFORMATION OF 17,18-CYCLOSTEROIDS

H-1-H-1 NMR couplings through four bonds ((4)J(H-H)) involving cyclopr opane hydrogens were calculated for model compounds by semiempirical m ethods and used for the C-13 and H-1 NMR spectral assignment of 17,18- cyclosteroids The couplings ((4)J(HH)) between cyclopropyl and non-cyc lopropyl hydrogens follow an angular dependence which resembles that o f allylic couplings, Solution conformations of rings C-D and the side- chain of 17,18-cyclopregnanes were determined from semiempirical molec ular orbital calculations, three and four bond H-1-H-1 coupling consta nts and NOE measurements.