Assignment of the electronic absorption spectrum of 1,4 : 5,8-anthracenediquinone (1,4 : 5,8-ADQ) has been carried out with the aid of magnetic circular dichroism and LCAO MO SCF CI calculations including all valence electrons. The lowest energy absorption region of 1,4 : 5,8-ADQ has been revealed to be composed of the n-π* transition or transitions. The higher energy absorption region has been concluded to consist of four π-π* transitions, which are regarded as Lb, La, Ba, and Bb in the Platt’s notation for anthracene. The above assignment of 1,4 : 5,8-ADQ has been experimentally confirmed with its linear dichroism spectra in stretched polyethylene sheets and its circular dichroism spectra in the β-cyclodextrin solution. The relationship between the absorption spectra of 1,4 : 5,8-ADQ and 1,4-naphthoquinone has been discussed from the experimental and theoretical points of view.
rac-2,2'-Dimethyl-l,I-biazulene rac-la['I has been resolved directly with the aid of HPLC using a commercially available ( + )-polytriphenyl-methyl methacrylate column[51 (RT,. The fraction of l a that 1 : X = H l a : X = CH, 16: X = OCHJ elutes first is levorotatory and exhibits a distinct negative C D couplet in the region 30000-40000 cm-' (Fig. 2), whereas the second fraction, which is dextrorotatory, gives a mirror image of the C D spectrum. Accordingly, rac-la is considered to be completely resolved.A given excited electronic state of azulene ( Fig. 3a) gives rise in rac-1,l'-biazulene 1 to two electronic states A and B of point group symmetry C2, of which the B state is energetically more stable (Fig. 3b). Both the A t A and B t A transitions of rac-1 originate from an excitation of azulene in which the long axis polarization has a particular value of the dipole strength161 and a non-zero rotational strength for all values of the dihedral angle a between the planes of the azulene groups except 0 and 180". Provided the absolute configuration is R (see Fig. 3c), a chirality consideration"' leads to the negative C D band associated with the B+A transition and to the positive band associated with the A t A transition (Fig. 3d). A similar consideration reverses the sign of C D bands for S-configuration; however, the B state is lower in energy than the A state.
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