Stereochemistry of bimolecular displacement in azavinyl systems crystal and molecular structure of N-(2,4-dinitrophenyl)-N-methylpivalohydrazonyl bromide

Abstract

Crystal structure determination and n.m.r. measurements show that hydrazonyl halides have the Z configuration [(6); X = Br, R¹= Bu^t. R²= N(Me)C₆H₃(NO₂)₂; X = Cl, R¹= Ph, and R²= N(Me)Ph, N(Me)C₆H₄NO₂, and N(Me)C₆H₃(NO₂)₂]. Reaction of the halides with methoxide ion in methanol or in methanol–dioxan is bimolecular and under these conditions the sole products formed are the Z-isomers (6; X = MeO), although in general the E isomers (7; X = MeO) are thermodynamically more stable. This observed retention of configuration at sp² carbon is discussed. Crystals of the title compound are monoclinic, space group P2₁/c, with Z= 4 in a unit cell of dimensions a= 7.35(5), b= 8.06(6), c= 25.60(10)Å. β= 95.0(1)°. The structure was determined by the heavy-atom method from visually estimated data and refined by full-matrix least-squares techniques to R 0.104 for 526 unique reflections.