Ab initio studies of structural features not easily amenable to experiment. 22. Structural aspects of a long-chain hydrocarbon (n-nonane) and a study of the transferability of electronic effects through CC single bonds

✍ Scribed by J. N. Scarsdale; H. L. Sellers; Lothar Schäfer; Norman L. Allinger

• Publisher: John Wiley and Sons
• Year: 1982
• Tongue: English
• Weight: 318 KB
• Volume: 3
• Category: Article
• ISSN: 0192-8651
• DOI: 10.1002/jcc.540030220

✦ Synopsis

Abstract

The molecular structure of the stretched form of n‐nonane, as a typical long‐chain hydrocarbon, was refined by geometrically unconstrained ab initio force relaxation on the 4‐21G level. The CC bonds and CH bond distances in the interior of the hydrocarbon chain are found to be longer (by about 0.001 Å and 0.002 Å, respectively) than those near the end of the chain. Similarly, interior CCC bond angles are 0.4° larger than the terminal angles. The variation of structural parameters with distance from the molecular ends levels off after the second carbon atom, and the geometry of methylene is practically constant from C~3~ on. However, if one end of the system is perturbed by moving the inplane methyl hydrogen away from equilibrium, the resulting destabilizing electronic effects are transmitted through the CC bond distance chain in such a way that significant perturbations are still experienced at C~5~. Molecular mechanics (MM2) gives a structure in which the small changes in bond lengths and angles with chain location are well reproduced.