The conformations of 3,4-dihydro-2H-1,5-benzodioxepin, and its derivatives as determined from their ultraviolet absorption spectra
Abstract
Derivatives of 3,4-dihydro-2H-1,5-benzodioxepin, with substituents in the aromatic and heterocyclic rings, have been prepared and the intensity of the Ph–O π→π* transition has been used to determine the angle of twist (θ) between the plane of the aromatic ring and the planes containing the oxygen bonds. The results obtained have been compared with the values of θ measured on molecular models. The unsubstituted heterocyclic ring appears to exist in a chair conformation, which is unaffected by substitution at the 2-, and 2- and 4-positions, but substitution at the 3-position, particularly by alkyl, methylene, or substituted methylene groups, produces a large increase in the content of the alternative skew conformation.