Ab initio study of the chair cope rearrangement of 1,5-hexadiene

✍ Scribed by M.J.S. Dewar; E.F. Healy

• Publisher: Elsevier Science
• Year: 1987
• Tongue: English
• Weight: 326 KB
• Volume: 141
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(87)85073-x

✦ Synopsis

Ab initio calculations up to the MP4SDQ16-31G* level are reported for the chair Cope rearrangement of 1,5-hexadiene. These are consistent with a recent AMI study, which showed the reaction to take place via a biradicaloid intermediate. Recent AM 1 [ I] calculations [ 21 seem to have established that the chair [ 31 Cope rearrangements [4] of 1,5-hexadiene (1) and its derivatives take place by the non-synchronous mechanism suggested by Doering et al. [ 51, involving a biradicaloid #' derived from the 1 ,Ccyclohexylene biradical ( ), as a symmetrical intermediate (SI) . These reactions had earlier been assumed to be typical synchronous "allowed" pericyclic processes [ 6 ] taking place via aromatic [ 71 transition states (TS; 3), a mechanism supported by a recent ab inito MC SCF study [ 81 of the chair rearrangement of 1. The two mechanisms can be distinguished by the (equal) lengths of the forming (CC,) and breaking (C,C,) bonds in the SI, these being expected [ 21 to be > 2 8, in an aromatic SI (3) but < 1.7 A in the biradicaloid (2). The lengths found in the AM1 [ 21 and ab initio [ 81 studies were 1.65 and 2.06 A, respectively.

/