Abstract:
A qualitative conformational analysis on cyclohexane, oxane and thiane structures bearing two geminal
electron-withdrawing groups and having two acetoxy substituents at the b and b’ positions has been performed. The
predominant conformation in thiane structures is determined by a preponderant hockey-stick effect. In the other structures, the
predominant conformation is determinated by the competition between stabilizing gauche and destabilizing steric effects
depending on the R1 and R2 bulks. Molecular mechanics procedure reproduces the conformational behaviour in compounds
25-32. Crystals of 29 are triclinic, P-1, a = 9.607(6), b = 13.437(8), c = 14.838(8) Å, a = 106.50(7), b = 98.61(6), b =
91.17º, V 0 1836(2) Å3, Z = 4,
Dx = 1.246 Mg.m-3, l (Mo Ka) = 0.71069 Å, m = 0.094 mm-1, F(000) = 736, T =293 ºK, R = 0.046 and
wR = 0.063, S= 0.88, for 2277 unique observed refelections with F20>8s(F20). The bond lengths and angles are normal
and do not reflect delocalization.