1,3,5,7-Tetra-t-butylbicyclo[4.1.0]hepta-2,4-diene: the first example of an alkyl-substituted norcaradiene in an equilibrium mixture with the cycloheptatriene tautomer

Abstract

1,3,5,7-Tetra-t-butylcyclohapta-1,3,5-trine actually contains its valence tautomer, the norcaradiene form (the title compound) in a ratio of 88.5:11.5 at 25 °C, as shown by ¹³C and ¹H n.m.r. spectroscopy, with ΔH° and ΔS° values of +5.3 ± 0.8 kJ mol^–1 and +2.0 JK^–1 mol^–1, respectively; two kinds of non-bonded repulsive interactions account for the effects of the t-butyl groups.