Conformational analysis of some alkylbenzene derivatives Part III: The barriers to rotation and the preferred conformations of some hydroxy‐alkyl groups in 1‐(1‐hydroxyalkyl)‐3,4,5‐trimethoxybenzenes

The barriers to rotation about the Cal‐Car bond of six hydroxyalkyl groups in 1‐C(OH)‐R1R2‐3,4,5‐trimethoxybenzenes have been determined from the coalescence of the PMR signals for the aromatic hydrogen atoms. The coalescence temperatures (°C) and the free energies of activation (kcal/mole) measured for the groups substituted with R1 and R2 are, respectively: But, H, −96, 8.7; But, Et, −38, 11.3; But. Pr, −40, 11.3; But, Bu, −38, 11.4; But, Pri, −8, 13.0; Pri, Pri, −42, 11.2. The heights of the barriers to rotation and the preferred conformations of the hydroxyalkyl groups with respect to the plane of the benzene ring are discussed.