Conformational energies and geometries of some oxa- and dioxabicyclo[3.3.1]nonanes from molecular mechanics

✍ Scribed by P. E. J. Peters van Cranenburgh; J. A. Peters; J. M. A. Baas; B. van de Graaf; G. de Jong

• Publisher: Elsevier Science
• Year: 2010
• Tongue: English
• Weight: 396 KB
• Volume: 100
• Category: Article
• ISSN: 0165-0513
• DOI: 10.1002/recl.19811000409

✦ Synopsis

Abstract

Empirical force field calculations have been performed on 2‐oxabicyclo[3.3.1]nonane, 3‐oxabicyclo[3.3.1]nonane and on 2,4‐dioxabicyclo[3.3.1]nonane and some of its methyl substituted derivatives. In 2‐oxabicyclo[3.3.1]nonane the cc and bc conformers are about equally strained. The calculations show that for 3‐oxabicyclo[3.3.1]nonane the cc, and for 2,4‐dioxabicyclo[3.3.1]nonane the bc, is the most stable conformation; the cc has a steric strain which is 8.3 kJ mol^−1^ higher. Replacement of the methylene units of bicyclo[3.3.1]nonane by ether oxygens seems to be mainly reflected in the amount of flattening of the wings in the various conformers. In the cc conformer of 3‐oxabicyclo[3.3.1]nonane the flattening is relatively small, whereas in 2,4‐dioxabicyclo[3.3.1]‐nonane the extent of the flattening is large with respect to the carbocyclic system. The calculated geometries and barriers to methyl rotation for the be conformer of 3,3‐dimethyl‐2,4‐dioxabicyclo‐[3.3.1]nonane and for the cb conformer of the 7,7‐dimethyl derivative show characteristic differences.