Use of semi-empirical models for calculation of B terms in MCD spectra. PPP model for [4N + 2] annulenes: a rule for substituent and heteroatom effects

✍ Scribed by Joseph Michl

• Publisher: Elsevier Science
• Year: 1976
• Tongue: English
• Weight: 335 KB
• Volume: 43
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(76)80599-4

✦ Synopsis

UGng the PPP model at monocxcltcd CI level and scvcral addItIonal blmphfying assumptions, the sign and magnitude of the lowest hICD (mdgnetlc circular dichrolc) band of a [4N + 21 nnnulcnc of arbitrary six perturbed by one or more substitucnts and/or hctcroatoms nrc cvaluatcd in closed form and r&ted to the difference bctwccn the energy ccparation of the two highest occupied molcculnr orbit& and the energy tcpamtion of the two lowest free molcculsr orbitals. This diffcrcncc can bc u~ally dcduccd by inspectIon from the nature and rclativc location of sub\titucnts, permittmg facile sign predictions without computations. The results establish a relation to the pcrimctcr model for polycyclic hydrocarbons and rl relation bctwcen MCI) dnd other forms of spectroscopy, in particular photoelectron and clcctron transmission spectroscopy