Carbon-13 chemical shifts of 4-substituted tricyclenes

Abstract

¹³ C Chemical shifts of a series of 4-substituted tricyclenes (1)–(10) are reported and are considered in relation to substituent effects and related structures. Chemical shifts of C(4) and the equivalent C(2) and C(6) cyclopropyl carbons correlate empirically with the electronegativity parameter, E_R. Smaller low-field β-shifts observed for C(3) and C(5) of the tricyclenes with respect to adamantanes (10) when the bridgehead substituent contains more than one atom heavier than hydrogen are rationalised in terms of the distances over which the diamagnetic shielding component of these structures has to operate. A good correlation is obtained between the substituent induced shifts of the exocyclic methyls C(10) and the equivalent pair C(8) and C(9) which are respectively to low and high field. The directions of these shifts extends a previously noted pattern for methyl induced shifts. ¹³C Shift data are reported for a limited number of 1-substituted bicyclo[2.2.2]octanes.