Semiempirical and ab initio conformational analysis of 2-methylene-8,8-dimethyl-1,4,6,10-tetraoxaspiro[4.5] decane with application of GIAO-SCF methods to NMR spectrum interpretation

J Mol Graph Model. 2000 Dec;18(6):567-80. doi: 10.1016/s1093-3263(00)00039-5.

Abstract

The GIAO-SCF method for calculating isotropic nuclear magnetic shielding values has been utilized to explain certain features in the 1H-NMR spectrum of 2-methylene-8,8-dimethyl-1,4,6,10-tetraoxaspiro[4.5] decane. Population distributions of the low-energy conformers based on their ab initio energies were used to produce weighting factors for the individual calculated shielding values to calculate the weighted average of the shielding values for a complete set of conformers. The differences in 1H chemical shifts between the hydrogens of the two methyl groups and between the axial and equatorial hydrogens in 2-methylene-8,8-dimethyl-1,4,6,10-tetraoxaspiro[4.5] decane were shown to be due to energy differences between the chair and boat orientations of the six-membered ring and contribution from a twist-boat conformation. Results suggest a hypothesis that intramolecular differences in chemical shift might be calculated to a greater degree of accuracy than chemical shifts calculated relative to a standard.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Magnetic Resonance Spectroscopy / methods
  • Models, Molecular
  • Molecular Conformation
  • Spiro Compounds / analysis*
  • Spiro Compounds / chemistry*

Substances

  • 2-methylene-8,8-dimethyl-1,4,6,10-tetraoxaspiro(4.5)decane
  • Spiro Compounds