The proton spectra of the vinyl groups in a series of 23 substituted styrenes have been analyzed as ABC spin systems. The proton chemical shifts are compared with the previously reported shielding data for the corresponding vinyl carbon nuclei. The series includes 12 meta-and para-substituted examples and 10 ortho-substituted examples. The effects of steric inhibition of conjugation on the vinyl proton parameters for some 2,6-disubstituted derivatives are considered in detail.

No abstract

The benzyl proton shifts in 11 series of para-substituted toluenes bearing different cc substituents have been determined. I n each series, a plot of the benzylic shift against the Hanimett o values of the parasubstituent is linear. The slope of these plots varies from 0.2 to 0.0 p.p.m./o. The variation is found to be conformationally dependent, a fact which is not explicable by current theory. A hyperconjugative interaction is proposed to account for these results and for several anomalies in the literature.Canadian Journal of Chemistry, 46. 1595 (1968) In the last decade a large number of authors have presented data showing a correlation between the effect of substituents on the chemical shifts (SCS) of protons on a benzene ring, and the Hammett o values of the substituents (1-3). More recently, correlations between o values and the SCS of protons in the side chain of aromatics have been reported (4, 5, and references therein). It is usually assumed that the SCS results from the inductive and resonance effects of the substituent, which alter the electron density at the ring carbon atoms. This change is then transmitted through the n electrons to the proton in question. An alternative explanation involving field and mesomeric effects (the F-M correlation) has recently been put forward by Dewar and Takeuchi (6).We wish to report the determination of the para-substituent effect on the benzylic proton shifts, in eleven series of compounds of the formula X-C6H5-CH,-Z.For each Z, at least five X substituents were studied whose range of o values was 0.95 or greater.' An example of the Hammett correlation for the benzylic protons of eight tetrahydropyranyl ethers is shown in Fig. 1. This plot is typical of 'All chemical shifts were measured on a Varian DA-60 nuclear magnetic resonance spectrometer using dilute solutions (0.2 M ) in CDCI,, except in the case of compounds whose methylene protons were magnetically non-equivalent. In these cases 0.3 M solutions were used. In each series, 0.1 M solutions were also studied and dilution shifts beyond the experimental error of 0.2 c.p.s. could not be detected. Satisfactory elemental analyses were obtained for all new compounds included in this study.

The temperature dependence of the formyl proton shieldings of 9-anthraldehyde and 9-phenanthraldehyde in chloroform solutions has been measured. Four concentrations in the range 0.5-5.0 mole % were examined over the temperature interval -60 to +90 "C. From these results, the enthalpies and entropies of formation have been estimated for the complex formed by the self-association of two aldehyde molecules. The calculations indicate the A H and AS values to be -1.9 f 0.3 kcal/mole and -6 rt 1 e.u., respectively. These results are compared with other available data.

The chemical shift of the benzylic protons in fifteen series of para-substituted toluenes bearing different groups in the alpha position are reported. In each series a plot of the chemical shift in tau units of the benzylic protons against the Hammett o value of thepara substituent is linear. The slopes of these plots vary from -0.20 to +0.01 p.p.m./o. The variation of slopes appears to be conformationally dependent, an observation at odds with current theory. In two rigid systems having the same geometry the slope has been found to vary from -0.12 to -0.18 indicating a dependence on other factors as well. The effect of solvent on the slopes has been determined, and shows no correlation with solvent dielectric properties.