Probe for Substituent Hyperconjugative Power: MCD (Magnetic Circular Dichroism) of the Benzene Lb Band

摘要

A simple molecular orbital analysis based on the perimeter model shows that the magnetic circular dichroism (MCD) of a substituted benzene provides information on the net pi-electron donar or acceptor effect of the substituent. The high sensitivity of the MCD measurement to weak substituent effects makes it particularly suitable for investigations of hyperconjugation. Experimental results for several dozen formally saturated substituents are reported. The observed trends are rationalized in terms of current bonding theory. Keywords: Substituent effects; Perimeter model; Magnetic circular dichroism.