A. Krzan et al., Novel associations of ortho quinone monooximes: Hydrogen bonded dimers of 4,6-di-tert-butyl-1,2-benzoquinone-2-monooxime, ACTA CHIM S, 48(2), 2001, pp. 229-239
Unlike previously reported X-ray structures of ortho quinone monooximes, wh
ich exhibit either intramolecular hydrogen bonding or chain-like structures
in the solid state, the sterically demanding 4,6-di-tert-butyl-1,2-benzoqu
inone-2-monooxime (DT) crystallizes as dimers. In crystals from toluene DT
forms dimers held together by two hydrogen bonds in a six-membered ring com
monly found for simple oximes, but not for orhto quinone monooximes. Crysta
ls from methanol contain DT dimers held together by two bridging mehtanol m
olecules, each of which participate in three hydrogen bonds. Although pheno
lic and quinonoid tautomeric forms of DT coexist in solution, with nonpolar
solvents favoring the aromatic phenolic tautomer, both crystals exist in t
he quinonoid form, independent of the solvent from which they were crystall
ized. These quinonoid forms are stabilized by intermolecular multi center h
ydrogen bonds and dipole-dipole interactions countering the effect of the l
oss of aromatic stabilization. With copper (II) perchlorate, DT yielded cry
stals of Cu(II)(HL)(L)CLO4, where HL=DT. HL and L ligands are coordinated t
o Cu(II) in a cis relationship.