An NMR and theoretical study on the conformational behaviour of benzylidenemalonaldehydes : A conformationally flexible unsaturated system

Abstract

The conformational behaviour of the methylenemalonaldehyde fragment of the title compounds is characterized by solvent and temperture dependencies of 1J( CH O), 3J( C HO,C H O), 3J( C HO,C H ), 4J(C H O,C H O) and 4J(C H O,C H ) spin-spin couplings as well some ab initio (STO-3G) and semiempirical level Molecular orbital calculations. The conformational behaviour of the couplings is also discussed on the basis of some INDO/FPT calculations. The conformations of the two formyls are strongly correlated, the trans - cis arrangements being favored. The conformation of the Z-formyl is determined by the steric interaction with the aromatic nucleus. The conformations of the formyls are sensitive to solvent and substitution on the aryl. Approximate populations and couplings of the sites are derived. There is some evidence about the non-planarity of the methylenmalonaldehyde fragnent. Complex formation with Mg(C10 4) 2 is reported.