The '"C NMR spectra of 20 polymethoxy-and/or methylenedioxyflavonols are reported. In key cases assignments have been made by examination of fully coupled spectra.

Spin-spin coupling between 14N and "C nuclei is observed in NMR spectra of some quaternary ammonium compounds, including a series of heterocyclic cations. 'J values are in the range 2.24.2 Hz.Instances of coupling through two and three bonds are also reported and these are correlated with "C chemical shift data for the structures concerned.13C, 14N NMR coupling Quaternary ammonium compounds; 'J, 'J and 5J values

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Details of the carbon-13 n.m.r. spectra of four 1,2,3,4-tetrachlorotetralins (naphthalene tetrachlorides) and of three 1,2,3,4-tetrachlor0-2-methyltetralins are presented. Chemical shifts of the signals attributable to the individual alicyclic and aromatic carbon atoms have been recorded and as far as possible identified by conventional methods ; lJC,= coupling constants have also been recorded. Several different types of 2Jc,H and 3Jc,H coupling constants have been identified from the details of the single resonance and partly decoupled high-resolution spectra. The results are discussed in relation to the known stereochemistry of these compounds.ELSEWHERE 2-4 lH n.m.r. spectroscopy has been used in conjunction with other techniques 5 9 6 to define the stereochemistry of the five known naphthalene tetrachlorides. Of these, the four whose structures are shown in diagrams (1)-( 4) were available to us in quantity sufficient for useful determination of their 13C n.m.r. spectra. Results from the use of this technique were expected to be helpful in extending knowledge of the factors determining chemical shifts and coupling constants in compounds of defined geometry; relatively few values of long-range (2 Jc, H and Jc, H) coupling const ants are available in the literature.'** The comparisons are extended by inclusion of values for the three 2-methylnaphthalene tetrachlorides ( 5) -(7) .l

Vicinal coupling constants in the 'H and "C NMR spectra of rcl,t-2,~-3,t-4-tetrachlorotetraIii change with temperature and solvent in a manner better explained by conformational equilibration than by intramolecular or solvent-determined distortions.The N M R spectrum of a compound which in solution can exist in more than one conformation in rapid equilibrium is characteristically intermediate between those of the individual conformers, so that the composition of such conformational mixtures can be determined if the spectral parameters of these conformers can be estimated.' Vicinal coupling constants have often been used for this purpose.'" In some cases, the spectral properties of the individual conformers can be determined but, more often, they have to be estimated either from known analogies or by long extrapolations. Idealized geometries have usually to be assumed, and it has been recognized4 that intramolecular distortions could produce angle changes which would be reflected by changes in these parameters, simulating changes in the proportions of the conformers. Weak association between solvent and solute can also change observed chemicalThe use of such measurements to calculate proportions of conformers suffers from a further difficulty, because structural factors affect the relationship between coupling constant, dihedral angle and bond angle.9-'3We have previously discussed the 'H and 13C N M R spectra of a number of isomeric or substituted 1,2,3,4-tetrachlorotetralins.14~1s For these compounds, as for cyclohexenes,16 conformational equilibria rapid on the N M R time-scale persist to quite low temperatures, and the observation of the spectra of two conformers separately, possible for some systems," is not practicable for reasons of solubility. For some of the isomers, the 3-bond coupling constants appear to be intermediate between that expected for either of the half-chair conformations; the results have been treated conventionally to estimate conformational proportions. These calculations are, however, subject to all the uncertainties mentioned above and, consequently, we have sought definite evidence that two conformations coexist in solution in proportions which affect the measured vicinal coupling constants. To do this, we have