Structure and reactivity of o-phthalaldehyde by X-ray, microwave, and molecular orbital calculations

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Results from a single crystal X-ray diffraction study on o-phthalaldehyde (1) revealed dihedral angles between the CHO groups and the benzene ring of 13(2)° and 27(2)°. In acetaldehyde solution, the 1H-NMR of 1 showed only broadening of the aldehyde singlet down to - 120 °C. The microwave spectrum of 1 was analyzed to give a non-zero second-moment Pcc of 0.662 u-A2, consistent with a non-planar structure in the gas phase with the CHO groups rotated out-of-plane by an average of 10 ± 2°. The X-ray determined structure, microwave experimental results and ab initio calculations at the MP2/6-31 + G(d) level all agree that 1 has a nonplanar structure. There is a remarkable agreement between the structure derived from X-ray and ab initio methods with electron correlation. Ab initio calculations at the Hartree-Fock level optimized to planar structures. © 2002 Elsevier Science B.V. All rights reserved.

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Journal of Molecular Structure