Cyclic-tri(N-methyl-meta-benzamide)s: Substituent effects on the bowl-shaped conformation in the crystal and solution states

Cyclic trimers of 3-(N-alkylamino)benzoic acid (calix[3]amides) with various substituents at the meta position of the phenyl rings were synthesized and the effects of the substituents on the crystal structures and energy profiles in solution were examined. The calixamides existed in a syn conformation in the crystal state, and this was also the major conformation in solution, especially in polar solvents. The energy barrier between syn and anti conformers in the solution was not significantly affected by substituents (12.7-14.0 kcal/mol). The effect of the substituent on the temperature dependence of the syn/anti ratio are discussed.