The crystallographic characterization of an unusual chemical reversal of photoisomerization

Abstract

lmines formed from pinacolone and primary amines could be acylated by acid chlorides or anhydrides to products hydrolysable to 1,3-diones. Renzoyl chloride with pinacolone benzylinline gave 3-(N-benzoyl-N-benzylamino)-4,4-dimethyl-1-phenylpent-2-en-1-one, both geometrical isomers of which were prepared. The yellow Z isomer was converted into the colourless E isomer on exposure to daylight and this change was reversed by brief treatment of the E isomer with aqueous ethanolic alkali. The Z and E isomers have been characterized crystallographically. The E isomer is monoclinic, C2/c, a 10.241(4), b 17.199(6), c 25.495(9) Å, β 100.45(3)º, Z = 8; R was 0.052 for 1947 'observed' reflections. The Z-isomer is orthorhombic, P2₁2₁2₁, a 18.24(1), b 15.60(l), c 7.871(4) Å, Z = 4; R was 0.061 for 902 'observed' reflections.