An INDO-MO study of the spectral properties and transannular interaction in [6]-helicene

The INDO-MO calculations on [6]-helicene reported here enable one to classify the four HOMO's as predominantly π, in contrast to other occupied MO's. A linear adjustment of these four HOMO's correlates well with the experimental photoelectron and optical spectra. Viewed through Mulliken's overlap population between overlapping rings, the transannular interaction in [6]-helicene appears to be unfavourable and therefore minimised. The use of a skeleton representation of the molecule is considered and found inadvisable.