The absorption and circular dichroism spectra of chiral olefins

摘要: Abstract Absorption and CD spectra over the quartz vacuum UV region down to 165 nm are reported for a range of chiral alkenes in vapour phase solution from +70° −185°C. A major couplet oppositely-signed bands with comparable band areas, near 48 55 kK, is observed number dissymmetric olefins some cases weaker Rydberg absorption found at lower frequency. The characterised by its sharp vibronic structure large blue-shifts produced on passing condensed reduction temperature. olefin opposite sign assigned near-complete mixing electric-dipole πx→πx* magnetic-dipole πx→πy* excitations, producing pair isotiopic same polarisation dipole strengths associated couplet. Three mechanisms discussed; sterically-induced π-bond torsion, first-order static field model, second-order dynamic-coupling model dependent, respectively, upon effective charge mean polarisability dissymmetrically-located substituent. latter two models give octant rule previously proposed empirically connecting rotational strength lower- higher-frequency member position substituent chromophore coordinate frame.