The proton resonance spectra of a variety of condensed aromatic compounds including benzene, naphthalene, anthracene, phenanthrene, pyrene, acenaphthylene and triphenylene were obtained in dilute CDCl 3 solution. Comparison of the proton chemical shifts obtained with previous literature data for CCl 4 solution shows small but significant differences. A previous model (CHARGE6) for calculating the proton chemical shifts of aliphatic compounds was extended to aromatic compounds. This was achieved by including an automatic identification of both five-and six-membered aromatic rings based on atomic connectivities plus a dipole calculation of the aromatic ring current. The ring current intensity in the molecules was calculated by two alternative methods. a) The ring current intensity in the individual benzenoid rings was a function of the number of adjoining rings and b) the molecular ring current was proportional to the molecular area divided by the molecular perimeter. This, plus the inclusion of deshielding steric effects for the crowded protons in these molecules, gave a good account of the observed chemical shifts. The model was also applied successfully to the non-alternant hydrocarbons of fulvene and acenaphthylene and to the aliphatic protons near to and above the benzene ring in tricyclophane and [10]cyclophane.The Huckel calculation of the π electron densities in CHARGE6 was used to calculate the π electron densities in substituted benzenes. The π-inductive effect was used to simulate the effect of CX 3 groups (X = H, Me, F) on the benzene ring. These together with the long range effects of the substituent groups identified previously allowed a precise calculation of the SCS of a variety of substituents on all the benzene ring protons.The model gives the first accurate calculation of the proton chemical shifts of condensed aromatic compounds and of the proton SCS in the benzene ring. For the data set of 55 proton chemical shifts spanning 3 ppm the rms error of the observed vs. calculated shifts was ca. 0.1 ppm. The model also allows the interpretation of the shifts in terms of the separate interactions calculated in the programme, i.e. π electron densities and steric, anisotropic and electric field effects. Previous correlations of the proton SCS with π electron densities and substituent parameters are shown to be over simplified. The relative proportions of these different interactions are very different for each substituent and for each ring proton.

The 1 H NMR spectra of a number of alkenes of known geometry were recorded in CDCl 3 solution and assigned, namely ethylene, propene, 4-methylcyclohexene, 1,4-dimethylcyclohexene, methylene cyclohexane (in CFCl 3 -CD 2 Cl 2 at 153 K), 5-methylene-2-norbornene, camphene, bicyclopentadiene, styrene and 9-vinylanthracene. These results together with literature data for other alkenes, i.e. 1,3-and 1,4-cyclohexadiene, norbornene, norbornadiene, bicyclo[2.2.2]oct-2-ene and a-and b-pinene, and other data allowed the determination of the olefinic shielding in these molecules. The shielding was analysed in terms of the magnetic anisotropy and steric effects of the double bond together with a model (CHARGE7) for the calculation of the two-and three-bond electronic effects. For the aromatic alkenes ring current and p-electron effects were included. This analysis showed that the double bond shielding arises from both anisotropic and steric effects. The anisotropy is due to the perpendicular term only with a value of 1c.C C/ of −12.1 × 10 −6 cm 3 mol −1 . There is also a steric deshielding term of 82.5/r 6 (r inÅ). The shielding along the p-axis changes sign from shielding at long range (>2.5Å) to deshielding at short range (<2Å). The model gives the first comprehensive calculation of the shielding of the alkene group. For the data set considered (172 proton chemical shifts) ranging from d = 0.48 to 8.39, the r.m.s. error of observed vs calculated shifts was 0.11 ppm.

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