Structure of α-benzylidene-(±)-piperitone, an exception to topochemical behaviour

Abstract

C₁₇H₂₀O, M_r=240.2, monoclinic, P2₁/n, a=6.116 (2), b=16.127 (3), c=14.417 (5) Å, β=96.62 (2)°, V=1412.5 (7) ų, Z=4, D_m=1.13, D_x=1.129 Mg m^-3, Cu Kα, λ=1.5418 Å, μ=0.454 mm^-1, F(000)=520.0, T=298 K, R=0.062 for the 1800 reflections used in the refinement. The two pairs of reactive double bonds which are related by a centre of inversion are properly oriented for [2+2] photocycloaddition. In spite of the favourable arrangement of the double bonds the molecule is photostable. A possible explanation for the inertness of the compound is provided in terms of a large atomic displacement of the styrene group upon excitation in the crystal lattice.