The literature on "C n.m.r. examinations of steroids has been reviewed and the shielding data for over 400 examples are tabulated. The assignments for each compound have been-ionsidered and, where necessary, revised in the light of more recent evidence and for consistency throughout each series. The methods available for assignments are reviewed and, in many cases, illustrated with specific examples. The major practical features concerning "C studies of steroids are discussed as a guide to the use of the technique. From the main body of shielding data, an extensive set of substituent effects has been generated to aid the examination of new systems. The ntility and the limitations of these effects are described.Since the iirst report in 1969 b] Roberts's group' clearly established the utility of C n.m.r. studies of steroids, more than fifty papers have appeared extending the original work. A key factor in the development of this field has been the advent of n.m.r. instrumentation which permits the routine acquisition of 13C shielding data. Some of these papers have provided compilations of some have examined substituent effects in the steroid f r a m e w~r k , '~-~~' 29-32 others have used 13C n.m.r. data to support or provide a stereochemical assignment or structural identification,3346 while a few have used the 13C data to derive information on mechanistic roblemsZ8 and complexation behavior of It seems an appropriate time to review the available data, to compile the shieldings for the steroids which have been examined, and to revise those assignments which more recent results indicate are in error. Included in this compilation are the previously unpublished data for more than fifty cholestanes, androstanes and pregnanes. The trends exhibited by the results are also considered in an alternative format by way of a table of substituent cffects. These effects are particularly useful for predictive purposes. The methods which have been used to make assignments of the signals in the steroid spectra are discussed and illustrated. Previous reviews and compilations of 13C n.m.r. spectra of more limited ranges of steroids have appeared.49ps0'79In this review, we have subdivided the discussion into four major sections. First, a general description of experimental methods and techniques for obtaining steroid spectra is presented and then the variety of approaches for making specific signal assignments is considered, with examples drawn fiom the main data compilation. In the third section the shielding results are discussed, particularly with regard to the assign-B

No abstract

The 13C nuclear magnetic resonance spectra of a series of 40 substituted anisoles have bcen obtained to investigate the eifects of substitution on the aromatic and methoxyl carbon shieldings. This \\.orlc estepds our studies on the variations of cheiilical shifts of carbon nuclei in side chains of aryl derivatives. ?'he question of steric hindrance to conjugative i~lteraction of a methoxyl group \vith an aromatic ring is co~lsidered on the basis of the present results. Evidence of a steric effect in compounds in which both ortho positions are substituted is presented.As an extension of a general survey of the 13C chelnical shifts for a variety of aromatic systems, it was of interest to examine the effects of substitution on the shieldings of the methoxyl and aryl carbon nuclei in a series of anisoles. There are two major features to be investigated. Lauterbur has demonstrated the existence of an additive relationship for the effects of substituents on aryl carbon shieldings in a number of benzene derivatives (1, 2), ivhich holds very well provided the substituent groups are not ortho to each other (1-5). Since the chemical shifts for the aromatic carbons in several monosubstituted benzenes have been reported by Spiesecke and Schneider ( G ) , it is possible to predict the shieldings in other derivatives by using these data and assuming additivity. I t seemed i\iorthn;hile to test these predictions for a number of anisoles, since only a few have been reported (1, 7).For the same series we have determined the variation of the methoxyl carbon shieldings wit11 substitution to find if these are sensitive to substituent polarity. Proton nuclear magnetic resonance studies have shon-n that rnethoxyl proton shifts are linearly related to the I-Iammett u parameter (8).The second feature concerns the effects of substituents on carbon shieldings in orthosubstituted systems. In general, it is found that the shielding effects of substituents on the aryl carbons are no longer additive, but it appears that the magnitude of the deviation from additivity is a crude measure of the steric hindrance to electronic interactions (2)(3)(4)(5)9).An examillation of h e 13C spectra of a series of ortho-substituted anisoles could therefore provide information on the steric inhibition of resonance of the rnethoxyl function. In addition, changes in the shielding of the methoxyl carbon nucleus itself should provide information about this point.For these reasons the 13C spectra of 11 meta-and para-substituted anisoles, 14 orthosubstituted examples, and 15 diortho-substituted anisoles have been obtained. The chemical shifts for the n~ethoxyl and aryl carbon nuclei have been measured. These results are the subject of this paper. EXPERIMENTAL Nlrclear i?/lag?zetic Reso?za?zce SpectraThe 13C spectra were determined a t a spectronleter frequent)-of 15.085 i\/Ic/s with samples containing l3C in natural abundance. The detailed procedure has been described (3). For the most part, the spectra were obtained with the neat liquids. In the case of solids, s...

13C nuclear magnetic resonance spectroscopy has revealed that cultures of the fungus Alternariasolani incorporate [1,2-13C2]acetate into the anthraquinone macrosporin (3) and the tetrahydroanthraquinones altersolanol A (4) and dactylariol (6) from a single octaketide chain. The carbon skeleton of 4-13Cx was incorporated intoto into 3, with 6 as a probable intermediate; there is also evidence that 4 may be a precursor of altersolanol B (5). The 2Hmr spectra show that deuterium from [1-13C1, 2-2H3]acetate is retained to a considerable extent in the C-methyl groups and the 1, 6, and 8 positions of 3 and 4 but is completely lost from the 3-position in 4. Zinniol (7), also a metabolite of the fungus, is a normal tetraketide.

The results of a study of the resonance position of the carbonyl carbon nucleus in an extensive series of carbonyl derivatives are reported. A discussion of the major factors affecting the position of these carbon resonances is presented and some of the potential applications of these data to chemical problems are indicated.

The 13C n.m.r. spectra of several norbornyl derivatives have been recorded to examine the variation of I3C shieldings with molecular geometry. Since it is well established that nonbonded interactions between vicinal carbon nuclei lead to pronounced upfield shifts, the so-called y effects, series of methyl-substituted norbornanes, norbornenes, norbornan-2-ones (norcamphors), and norborn-5-en-2-ones were prepared a s model systems having a variety of y interactions between vicinal methyl groups. The observed shifts of these methyl carbons are considered in terms of the dihedral angle relating the vicinal nuclei. The use of specific deuterationfor unequivocal signal assignments ofcarbons geminal and vicinal to the site of deuteration is illustrated.Les spectres 1.m.n. I3C de plusieurs derives du norbornyle ont ete enregistres afin d'etudier la variation de I'effet de blindage du I3C en fonction de la geometrie moleculaire. Puisqu'il est bien connu que d e s interactions non-likes entre des carbones vicinaux entrainent des deplacements du signal vers des champs Cleves, relation connue sous le nom effets-y plusieurs norbornanes, norbornenes, norbornanones-2 (norcamphres) et norbornkne-5 ones-2 substituis par des groupes methyles ont i t 6 prCpares afin de servir d e modkles posskdant diffkrentes interactions y entre des groupes methyles vicinaux. O n a utilis6 la deutCration spicifique pour attribuer sans arnbiguite les signaux se rattachant aux carbones gCmines et vicinaux au site d e deuteration.[Traduit par le journal]Can. J . Chem., 51, 2893Chem., 51, (1973

The substituent effects of the hydroxyl group on the 13C shieldings of the trans-decalols and the 10-methyl-trans-decalols have been determined. The shifts for the carbons three and four bonds from the site of substitution depend strongly on their orientation with respect to the hydroxyl group. While the latter have not been widely recognized, these 6 effects are valuable for spectral analysis and stereochemical assignments since these range up to 3.4 p.p.m. I n direct contrast to the well established trends for y effects, steric crowding of 6 nuclei causes marked downfield shifts. The corresponding effects in several steroids are illustrated.On a determine les effets de substituent du groupe hydroxyle sur le blindage du 13C des transdecalols et des methyl-10 des trans-dicalols. Le deplacenient des carbones qui se trouve a trois et quatre liens du site de la substitution montre une grande dependance sur l'orientation par rapport au groupe hydroxyle. Mtme si ces derniers effets n'ont pas CtC reconnus d'une facon generale jusqu'a maintenant les effets sont trirs utiles pour I'analyse spectrale et la dktermination stCrCochimique puisqu'ils ont des valeurs allant jusqu'a 3.4 p.p.m. L'encombrement sterique des noyaux cause un deplacement chimique marque vers les bas champs et ceci en opposition directe avec les tendences bien Ctablies pour les effets y. On illustre enfin des correspondents dans plusieurs steroides.

The 15.1 hiIc/s 13C n.m.r. spectra of 55 substituted acetophenones have been examined and the chemical shifts of the various carbon nuclei determined. 'This series included a variety of monosubstituted cases (ortho, meta, and para) a s well as several polysubstituted examples. The factors contributing to the observed shieldings of all carbon nuclei are considered. The aromatic shieldings are compared with previous results for other aromatic derivatives. The application of the carbonyl shifts to the study of steric inhibition of resonance in these derivatives is examined critically. T h e shieldings of the acetyl methyl and para-carbon nuclei are found to offer confirmatory evidence for the existence of steric hindrance to coplanarity of the acetyl group ill several ortho-substituted cases.