Kiesswetter, Roland and Pustet, Nikola and Brandl, Friedrich and Mannschreck, Albrecht (1999) Chiral 2H-pyrans, Part 10 - 1 ',3 ',3 '-Trimethyl-6-nitrospiro[2H-1-benzopyran-2,2 '-indoline]: its thermal enantiomerization and the equilibration with its merocyanine. TETRAHEDRON-ASYMMETRY, 10 (24). pp. 4677-4687. ISSN 0957-4166,
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The enantiomers of the title compound, the important photochromic material (RS)-1b, have been enriched semipreparatively by liquid chromatography. As a consequence, we were able to determine the barrier of the thermal interconversion (R)-1b=(S)-1b via time-dependent polarimetry, amounting to Delta G(not equal) kJ/mol at 22.0 degrees C in d(6)-DMSO (Table 2). The thermal equilibration of the corresponding merocyanine 2b was monitored in d(6)-DMSO by time-dependent H-1 NMR, resulting in Delta G(1)(not equal)=102.8 and Delta G(2)(not equal)=92.0 kT/mol at 22 degrees C (Table 1). This means that, starting from (RS)-1b, the opened isomer 2b is attained by a slow reaction (Delta G(1)(not equal)=102.8 kJ/mol, Fig. 4). Therefore, the merocyanine 2b cannot be identified with the intermediate required for the fast process of C(sp(3))-O bond cleavage (Delta G(not equal)=85.9 kJ/mol) upon the above enantiomerization of (RS)-1b. Apparently, these two thermal isomerizations (Fig. 4) are independent of each other. The structure of the unknown intermediate of the interconversion (R)-1b reversible arrow(S)-1b must therefore differ from the known one of merocyanine 2b. (C) 2000 Elsevier Science Ltd. All rights reserved.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | CHIROPTICAL DETECTION; CIRCULAR-DICHROISM; STEREODYNAMICS; RACEMIZATION; SPIROPYRAN; BARRIERS; |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Organische Chemie > Alumni or Retired Professors > Prof.Dr. Mannschreck |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 06 Dec 2022 09:19 |
| Last Modified: | 06 Dec 2022 09:19 |
| URI: | https://pred.uni-regensburg.de/id/eprint/48762 |
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