Wiley

Carbon‐13 NMR spectra of various 8‐aryl‐8‐azabicyclo[3.2.1]oct‐3‐en‐2‐ones and other related compounds, including tropinone, were determined, and the predominant conformation at the bridgehead nitrogen was established. The full assignment of resonances from proton decoupled and coupled spectra was based on the analysis of the splitting pattern and characteristic chemical shifts. The use of the determined ¹³C NMR spectra in the assignment of ¹³C NMR data in related but more complicated structures is also proposed.

The preferred solute conformation of ethyl 3α‐phenyltropane‐3β‐carboxylate hydrochloride, the tropane analogue of pethidine, is shown to be a piperidine chair with an axial 3‐phenyl substituent by analysis of its ¹H NMR characteristics and spectral comparisons with model compounds. Conformational studies of synthetic intermediates are also reported and favoured boat forms identified for 3α‐diphenylhydroxymethyl‐3β‐tropanol and 3α‐phenyl‐3β‐tropanyl phenyl ketone. In the hot‐plate test for analgesia performed on mice, ethyl 3α‐phenyltropane‐3β‐carboxylate is about 1·5 times as effective as pethidine.

An approach for the automatic assignment of ¹³C spectra, based on the chemical shift/charge density relationship, is suggested. All permutations of spectral signals are computer‐generated, and for every permutation a least squares adjustment is carried out. The permutation presenting the highest correlation coefficient, or the lowest Hamilton's agreement factor, is considered to be correct. The application is exemplified by the ¹³C chemical shifts of a series of aromatic compounds. It is shown that more reliable assignment is achieved if the considered permutations are restricted by taking intoaccount the signal multiplicity.

Inverted files of spectral features should be employed when searching for identical or similar spectra. The efficiency of interescting the entries for chemical shifts with a small deviation is very high for larger molecules and incomplete spectra. A novel spectral code describing the spectral appearance in hierarchical order (SAHO) facilitates the search for complete spectra with a relatively high tolerance of the chemical shifts. A vailable information on the chemical composition of the molecule, as well as the incusion of SFOR‐multiplicities, will further narrow down the number of suitable reference compounds.

The principles of the theoretical calculations of the carbon atom screening constant are reviewed. The Independent Electron, SCFMO and Valence Bond formulae are briefly discussed, and the relative importance of the different terms involved in an approximate decomposition of σ¹³C are pointed out. The variations of the excitation energy ΔE, the mean distance between the nucleus and 2p electrons, and the electronic charges and bond orders with the structure are presented. The nature of the steric effect is also explained. In a second part the various empirical correlations which make an evaluation of δ¹³C from structural and physical properties possible are shown. The actual substituent parameters of the main classes of compounds are listed and worked examples given to make the use of the tables easier. The correlations between δ¹³C and the electronic charge, electronegativity, Hammett‐Taft constants, electric field effects, geometrical parameters, spectroscopic data (electronic transitions, screening of other nuclei) and pH are also discussed with a view to appraising the carbon screening.

The ¹³C NMR signals of some mono‐ and disubstituted aryl compounds were assigned by means of empirical additive substituent parameters and information taken from fully coupled spectra. This assignment was compared with that obtained with the help of the method of automatic assignment of the signals based on the linear relationship between ¹³C chemical shift and charge density. The results show that in the cases of XR substituents (X = O, NH and R = H, CH₃, CH₂CH₂OH) a good correlation is observed and the automatic assignment is correct. In contrast, in the cases of CH₂CH₂Y substituents (Y = OH, NH₂, Cl) a worsening of the correlation is observed and the automatic assignment is not correct.

It is suggested that for compounds with a preliminarily known assignment, the automatic assignment can serve as an additional criterion for the reliability of the linear relationship between ¹³C chemical shift and charge density.

The conformational preferences in solution of eight new open‐chain and cyclic aromatic sulphides containing pyridine or 1,3,4‐thiadiazole units have been investigated, parallel to those of some structurally related phenyl sulphides, by means of ¹H NMR spectroscopy. The results obtained have shown that replacement of phenyl by the pyridyl or the 1,3,4‐thiadiazolyl moieties induces slightly different propeller arrangements, ascribed to the higher conjugative tendency of both electron‐deficient heteroaromatic rings, in all open‐chain mixed sulphides, in opposition to the skew arrangements observed for phenyl sulphide derivatives. No prominent differences have been found for cyclic sulphides, which preferentially adopt the sterically unhindered saddle shape conformation.

The ¹³C NMR spectra of β‐methyl‐β‐nitrostyrene and its nine mono‐ and dimethoxy‐derivatives have been determined. Chemical shift data are presented and analysed in a self‐consistent manner which allows most of the signals to be unambiguously assigned. Trends in the data can be interpreted in terms of the conformational properties of the variously‐substituted compounds.

The olefins Ph₂P(X)CHCHR [X=lone pair, O, S, Ch₃I; RCh₃, ph, P(X)ph₂] have been prepared and their ¹H, ¹³C and ³¹P NMR spectra measured. trans ³J[P(IV)C] (range 18.3–25.7 Hz) is greater than cis ³J[P(IV)C] (range 6.9–11 Hz) but this relationship does not hold for P(III) compounds. In the ³¹P spectra the E isomer absorbs to higher field than the Z isomer for P(III) and P(IV) compounds. The ¹H data are in accord with previous results; average substituent shielding coefficients for ph₂P(X) substituted alkenes are reported.

Le spectre de RMP de quelques nouveaux oxazaphosphorinanes‐1,3,2 est analysé. Dans un cas, après élimination du couplage entre les protons et le phosphore, on a affaire à un système ABKLXY particulier dans lequel certaines constantes de couplage entre protons vicinaux sont nulles. Le système ABKLXY où J_AK = J_AL = J_BK = J_BL est étudié, ce qui permet d'accéder à la plupart des paramètres du composé considéré. La conformation du cycle est précisée, la valeur de l'enthalpie libre conformationnelle est donnée et, pour l'oxazaphosphorinane‐1,3,2 précédent, l'angle de torsion des liaisons C₄C₅ et C₅C₆ est calculé.