Ab initio prediction of optical rotation: Comparison of density functional theory and Hartree-Fock methods for three 2,7,8-trioxabicyclo[3.2.1]octanes
Version of Record online: 11 APR 2002
Copyright © 2002 Wiley-Liss, Inc.
Volume 14, Issue 4, pages 288–296, 2002
How to Cite
Stephens, P.J., Devlin, F.J., Cheeseman, J.R. and Frisch, M.J. (2002), Ab initio prediction of optical rotation: Comparison of density functional theory and Hartree-Fock methods for three 2,7,8-trioxabicyclo[3.2.1]octanes. Chirality, 14: 288–296. doi: 10.1002/chir.10039
- Issue online: 11 APR 2002
- Version of Record online: 11 APR 2002
- Manuscript Accepted: 3 AUG 2001
- Manuscript Received: 20 JUN 2001
- NSF. Grant Number: CHE-9902832
- optical rotation;
- density functional theory (DFT);
We report ab initio calculations of the frequency-dependent electric dipole-magnetic dipole polarizabilities, β(ν), at the sodium D line frequency and, thence, of the specific rotations, [α]D, of 2,7,8-trioxabicyclo[3.2.1]octane, 1, and its 1-methyl derivative, 2, using the Density Functional Theory (DFT) and Hartree-Fock/Self-Consistent Field (HF/SCF) methodologies. Gauge-invariant (including) atomic orbitals (GIAOs) are used to ensure origin-independent [α]D values. Using large basis sets which include diffuse functions DFT [α]D values are in good agreement with experimental values (175.8° and 139.2° for (1S,5R)-1 and -2, respectively); errors are in the range 25–35°. HF/SCF [α]D values, in contrast, are much less accurate; errors are in the range 75–95°. The use of small basis sets which do not include diffuse functions substantially lowers the accuracy of predicted [α]D values, as does the use of the static limit approximation: β(ν) ≈ β(o). The use of magnetic-field-independent atomic orbitals, FIAOs, instead of GIAOs, leads to origin-dependent, and therefore nonphysical, [α]D values. We also report DFT calculations of [α]D for the 1-phenyl derivative of 1, 3. DFT calculations find two stable conformations, differing in the orientation of the phenyl group, of very similar energy, and separated by low barriers. Values of [α]D predicted using two different algorithms for averaging over phenyl group orientations are in good agreement with experiment. In principle, the absolute configuration (AC) of a chiral molecule can be assigned by comparison of the optical rotation predicted ab initio to the experimental value. Our results demonstrate the critical importance of the choice of ab initio methodology in obtaining reliable optical rotations and, hence, ACs, and show that, at the present time, DFT constitutes the method of choice. Chirality 14:288–296, 2002. © 2002 Wiley-Liss, Inc.