Phenylhydrazone derivatives of Meldrum's acid: crystal and molecular structures of 2,2-dimethyl-1,3-dioxan-4,5,6-trione 5-(2-nitrophenylhydrazone)(1) and 2,2-dimethyl-1,3-dioxan-4,5,6-trione 5-(2-chlorophenylhydrazone)(2)

Abstract

A series of phenylhydrazone derivatives of 2,2-dimethyl-1,3-dioxan-4,6-dione (Meldrum's acid) and of the corresponding 2-phenyl compound has been prepared. Their i.r. and ¹H n.m.r. spectra are discussed in terms of the extent of intramolecular hydrogen bonding. With ortho-nitro-group substituents on the aromatic ring, enhanced low-field chemical shifts of the order δ_NHca. 15 imply a bifurcated hydrogen-bonding environment. Compound (1), C₁₂H₁₁O₆N₃, crystallises in the monoclinic space group P2₁/a with a= 7.178(7), b= 13.976(12), c= 13.042(11)Å, β= 102.7(1)°, Z= 4. Compound (2), C₁₂H₁₁ClO₄N₂, crystallises in the orthorhombic space group P2₁2₁2₁ with a= 14.279(12), b= 18.950(15), c= 9.460(12)Å, Z= 8. Both structures were solved by the statistical method using the Shel-X 76 system of programs and refined using full-matrix least squares. The numbers of reflexions used in refinement and the final R values are (1), 1 369, 0.069 and (2), 1 490, 0.080, respectively. In (1) the NO₂⋯ HN and CO ⋯ HN separations confirm the ortho-nitro-involvement in bifurcated intramolecular hydrogen bonding; in (2), though there is still substantial CO ⋯ HN intramolecular hydrogen bonding the ortho-chloro atom is not involved. For (2) the ring fragment (I) is essentially planar but this is not so for (1). The 1,3-dioxan-4,6-dione cyclic system adopts a boat conformation in each structure. There is no intermolecular hydrogen bonding.