IR spectra and structure of benzylidenemalononitrile and its cyanide, methoxide and heptylamine adducts: experimental and ab initio studies

The potassium cyanide, alkali-metal methoxide and heptylamine adducts of benzylidenemalononitrile were prepared as dimethyl sulphoxide (DMSO) and DMSO-d(6) solutions; their structures were studied by IR spectroscopy and ab initio force field calculations. The cyanide and methoxide adducts have a carbanionic structure, whereas heptylamine forms a zwitterion. The IR spectra of the adducts studied are characterized by very intense, low frequency v(CN) bands with a strong v(CN)(s)-v(CN)(as) splitting. The changes in the structure and force field of benzylidenemalononitrile accompanying its conversion into the adducts studied are essential and are spread over the whole molecule. The anionic charge is localized mainly within the dicyanomethide groups of the adducts. (C) 1997 Elsevier Science B.V.