LOW-TEMPERATURE X-RAY-DIFFRACTION ANALYSIS OF 2.1.1(2,5).1(4,7).1(8,11).0(1,8).0(2,7)]HEXADECANE - DSC, MM2 AND H-1-NMR STUDY OF ITS [2+2]RETROCYCLOADDITION TO AN ISOMERIC DIENE

The synthesis of pure 3 has been achieved by deiodination of 1 with Na -K alloy at r.t. and by [2+2] photocyclization of diene 4. X-ray diffr action analysis at -30 degrees C of the thermally unstable 3 shows the cyclobutane ring to be highly rectangular with large central and shor t lateral bonds. Also, the C4-C5 and C10-C11 bonds in 3 and diene 4 ar e very large. A clear neat DSC conversion of 3 to 4 allowed us to obta in the Delta H and the Ea values for this transformation. Delta H is i n good agreement with MM2 calculations, while Ea compares well with ki netic measurements in CDCl3 solution. Copyright (C) 1996 Elsevier Scie nce Ltd