Abstract-The carbon-1 3 NMR spectra of 16 aliphatic phosphorus compounds with -PCI2, -P(OCH,),, -P(CH& or -PS(CH,), groups were determined and interpreted on the basis of the usual a,B-deshielding and y-shielding effects. The a-effects of all the groups were quite large (15 to 30 pprn), though the B-effects were small (0 to 3 ppm). The y-effects were also small (0.2 to 1.6 ppm), but of significance in suggesting reduced steric compression relative to that found for methyl and most of the common organic functional groups. This may be attributed to the greater length of the C-P bond. The phosphorus-31 NMR spectra of these compounds also show the existence of interaction with y-carbons by exhibiting small additive upfield shifts.CARBON-13 NMR spectroscopy has already found use in structural studies of organophosphorus compounds, especially cyclic derivatives, but relatively little systematic work on the effects of the common phosphorus functions on alkyl carbons has been reported. The literature to about 1970 has recently been reviewedla and since that time only one additional study (on tertiary phosphines) has appeared.2 We felt the need for additional basic information in conjunction with studies on phosphor inane^^ and on alicyclic compounds with phos-

Placing a methyl at the 3 or 4 position of 1-methylphosphorinane results in conformational equilibria for both the cis and trans isomers that are strongly biased toward the form with equatorial C-methyl. This remains true when the phosphines are converted to sulfides, oxides, or methiodides. The steric demand of C-methyl is therefore considerably greater than that of P-methyl, a fact predicted fpr 1-methylphosphorinane by its AGO value of +0.35 kcal/ mol. I3C NMR spectroscopy was especially helpful in qualitatively analyzing the equilibria; the C-methyl and its carbon of attachment in a pair of isomers had little chemical shift variability, while P-methyl differed by 4-6 ppm, always with the axial methyl relatively upfield. Both the sulfides and the oxides have ring carbons 3 and 5 at higher field (2-3 ppm) when the sulfur or oxygen atoms are axial. This greater y effect for a single-atom substituent on phosphorus over a methyl group has been observed previously for the case of S, but not for 0. While 31P NMR shifts were sensitive to the stereochemistry about phosphorus, no consistency in the direction of the effect was present. For the phosphines, axial methyl caused the expected relatively upfield shift. This was observed also for the sulfides, hut the reverse effect prevailed for the oxides.Phosphorus-substituted phosphorinanes are of considerable interest because of the predominance of the conformer with axial substituent, over that with equatorial a t room temperature.2 For the 1-methyl derivative, the equilibrium constant (a s e) is estimated to be about 0.55, which gives AGO = +0.35 kcal/mol at 27 "C. This unusual result stems from a combination of a rather low enthalpy difference for the conformers (AHo = -0.68 kcal/mol) and a significant entropy effect (ASo = -3.4 eu). 1-Methylarsenane was later reported by another group to exhibit similar p h e n~m e n a .~We have continued our investigation of the 1-methylphosphorinane system by considering the consequences of placing methyl a t either the 3 or the 4 position, and then of adding sulfur, oxygen, or methyl to phosphorus to increase its covalency in these compounds. The synthesis and spectral properties of all of these compounds are reported in the present paper. Our major probe of the conformational changes occurring in these families has been I3C NMR spectroscopy; we have previously employed this technique for hydroxy4 and keto5 derivatives of phosphorinanes and have witnessed a number of useful effects. 31P NMR spectroscopy has also figured in our earlier studies and we have examined our new C-methyl compounds by this technique also.The spectral data we have accumulated are best interpreted on the basis of perturbation of the conformational equilibrium for the parent 1-methylphosphorinane (1). Thus, a more CH la l bspace-demanding group such as CH3 (AGO = -1.7 kcal/mol in cyclohexanes; for thianes,6 -1.80 f 0.10 for 4-CH3 and 1.40 f 0.07 for 3-CH3) placed on ring carbon 4 should control the equilibrium and the P-CHs group will be forced into greater oc...