Towards more reliable prediction of formaldehyde multinuclear NMR parameters and harmonic vibrations in the gas phase and solution

Ab initio calculations at the Hartree-Fock level using London atomic orbita ls have been performed to investigate the basis set dependence of theoretic ally calculated multinuclear NMR parameters, both isotropic and anisotropic parts, of formaldehyde in the gas phase and in solution. A number of diffe rent families of basis sets, including the 6-311++G** and Sadlej's polarize d basis sets, and the correlation-consistent polarized split-valence basis sets of Dunning (cc-pVxZ) (x = D,T,Q,5,6) have been investigated. The conve rgence of the closely related augmented and core-valence correlation-consis tent basis sets has also been studied. The molecular properties of formalde hyde obtained from the RHF calculations in the gas phase have been compared with the properties calculated using B3PW91-DFT. The changes in the nuclea r shieldings and the harmonic vibrational frequencies of formaldehyde in so lvents of different polarity have been investigated at the Hartree-Fock lev el using a dielectric continuum model. Good agreement between the experimen tal and calculated solvent shift of the C=O stretching frequency of formald ehyde in cyclohexane and acetonitrile has been obtained. The results of thi s study provide a deeper insight into the nature of experimental NMR data o f formaldehyde and the reason for their low accuracy. (C) 1999 Elsevier Sci ence B.V. All rights reserved.