ISSN:
0009-2940
Keywords:
Indigo
;
Calculations, AM1
;
cis/trans Isomerization
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
AM1-SCF and AM1-SDCI calculations have been carried out for indigo and three conformers of N,N′1-diacetylindigo in their cis and trans configurations. The molecular structure of trans- N,N′1-diacetylindigo was determined by X-ray diffraction. The calculated ground-state data obtained within the SCF approximation (relative energies, structural parameters) are in excellent agreement with the corresponding experimental values. Potential energy curves (PEC) for the isomerization reaction cis/trans in several electronic states were obtained from AM1-SDCI calculations. For N,N′1-diacetylindigo the ground state PEC has a maximum at a torsion angle about the central C—C bond of 90°, whereas the S1- and T11-state PEC's show minima at the corresponding geometry. For indigo itself significant barriers to the photoisomerization in the S1- and T11-excited states are predicted because of increased NH…OC hydrogen bonding. The results provide an explanation for the phototropic behaviour of N,N′1-diacetylindigo and the photostability of indigo. The calculated enthalpies of activation for the isomerization process cis → trans in the ground state compare well with available experimental data, thus rendering feasible the prediction of the thermal stability of cis isomers not yet synthesized.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19931260423
