Chemical Shifts of Axial and Equatorial α-Protons in the N.m.r. of Steroidal α-Haloketones

Abstract

N.m.r. of Steroidal a-HaloketonesSir:The discovery' that axial hydrogens are more highly shielded than corresponding equatorial ones increased the use of n.m.r. chemical shift data in structural studies of cyclohexane systems. Interpretations of this differential shielding have been p r o p o~e d~,~~,~~d and scattered examples of exceptions to the rule have been reported.lbs4 We have found that a carbonyl group adjacent to a monohalogenated carbon in ster-(1) (a)

Correlation between optical rotation sign and conformation of γ-butyrolactones

“…And because, for compounds 6-10, the relative order of the chemical shifts of H 3a and H 3b is d H 3a > H 3b , it can also be seen that compounds 6-10 all adopt conformation II. Apparently, this result agrees with the previous observations that in steroidal a-acetoxy ketones, 12 a-halo ketones 13 and a-bromo cyclohexanones, 14 the a-protons of the carbonyl groups resonate at lower magnetic fields when axial than when equatorial.…”

Cyanoethylations and Michael additions. II. The synthesis of allylic cyclohexenols by γ-cyanoethylation of α,β-unsaturated aldehydes and ketones. Part II

“…maximum d L corresponding to the stretching freq~~encies of the carbonyl function, this effect being, however, greater for the equatorial substituent of ketone 9; thus, the nitrile group behaves in this respect not like a bromine, chlorine, or acetoxy substituent, but rather like a fluorine substituent (23e, 27).' 1°The axial 162-proton of ketone 9 is more deshielded than the equatorial 162-proton of ketone 10, which corresponds well to the situation in the case of a-halogenated cyclohexanones (24). We have already discussed the deshielding by the axial nitrile function of the 18-methyl group of ketone 10.…”

CuII and AuIII Complexes with Glycoconjugated Dithiocarbamato Ligands for Potential Applications in Targeted Chemotherapy

“…The protons of the hydroxy groups of the pyranose ring couple with the adjacent methynic protons and give rise, in the case of GluDTC, to three doublets (protons 7, 8, 9) and a triplet (proton 10), at 4.95, 4.87, 4.83, and 4.50 ppm, respectively (Table ). Generally, the resonances of the equatorial protons in the pyranose ring are shifted to lower fields relative to the axial protons …”

“…Generally,t he resonances of the equatorial protons in the pyranose ring are shifted to lower fields relative to the axial protons. [47,48] In particular,a ll methynic protons in the b-d-glucoside ligand experiencet he most shielding effect relative to the axial counterparts of the b-d-galactoside and a-d-mannoside derivatives (except for the 1 Ha tC 1 ). For example, the protona tt he positionC 2o ft he formerr esonates at highest field (2.93 ppm) with ad ifference of 0.66 ppm with respect to the equatorial proton at the same positiono ft he ManDTC (3.59 ppm).…”