Substituent effects on the chemical shifts of the bridge protons of benzonorbornenes

Abstract

The substituetlt effects on the chemical shifts of the Cg bridge protons in a scries of 6-substituted benzonorbornenes and benzonorbornadienes, and on those of the Cz protons in 6-substituted 2-indanols, were investigated. They were linearly correlated with the modified Hammett relationship 7, -7, = p(um + uP)/2. The p values obtained from the anti-Co protons in the bornenes and bornadienes were slightly but significantly larger than those from the corresponding syn protons, whereas no significant difference was observed between the p values obtained from syn-9-benzonorbornenols and the indanols. The larger pa,,, values were explained in terms of a stereospecific electronic interaction between the T-electron system of the benzene ring and the orbital system of the bridge carbon. In addition, it was shown that the above modified Hammett relationship gives generally a good agreement with the substituent effects on the aliphatic constituents of benzocyclenes and analogous compounds.

Effect of substituents on the chemical shift of benzylic protons

“…In addition similar correlations have been observed for protons in the side chains of toluenes (4-7), phenols (8), anisoles (9), dihydrocinnamic acids ' (lo), cyclopropanes (1 l), and benzonorbornenes (12). The mechanism by which a substituent exerts its effect is a subject of some contention.…”

“…We must therefore seek a new explanation for our results. It is proposed that either the paramagnetic shielding term in the Ramsay formula is not negligible A somewhat analogous explanation involving homobenzylic resonance has been proposed by Tanida and co-workers (12) to account for the stereochemical difference between the p's for the syn and anti 7-hydrogens in a series of benzonorbornenes. We hope that additional results will provide further evidence regarding the mechanism by which an SCS is produced.…”

A Novel Approach to the Rare 4- and 5-Alkylindan-2-ols

“…Only very few publications 1,2 deal with the preparation of 4-and 5-alkylindan-2-ols 4 and 5. To the best of our knowledge, no general synthetic route to them, has yet been described.…”