Kiesswetter, Roland and Burgemeister, T. and Mannschreck, Albrecht (1999) 1 ',3 ',3 '-trimethyl-6, 8-dinitrospiro [2H-1-benzopyran-2,2 '-indoline]: Fast thermal enantiomerization and slow thermal equilibration with a ring-opened isomer. ENANTIOMER, 4 (3-4). pp. 289-296. ISSN 1024-2430,
Full text not available from this repository. (Request a copy)Abstract
The transformation of the title compound (RS)-2 into the merocyanine 1 was studied by time-dependent H-1-NMR in DMF-D-7 at 22 degrees C. An equilibrium containing 1.9% (RS)-2 is established; the free enthalpy of activation for the (XS)-2 --> 1 process amounts to 101.3 kJ mol(-1). The interconversion of the enantiomers of the title compound was studied by temperature-dependent H-1-NMR in DMF-D-7. The barrier to ring opening (60.1 kJ mol(-1), 23 degrees C) was determined for the first time. Apparently (RS)-2 represents the 2H-1-benzopyran with the lowest Delta G not equal-value for this process which occurs as often as 155 times per second at 23 degrees C. The characterization and all H-1-NMR measurements of (RS)-2 were facilitated by its isolation as a solid. The two reactions, namely interconversion of enantiomers and transformation into a merocyanine, are found to be kinetically independent of each other. Their mechanisms are discussed on the basis of the scheme of free enthalpy changes.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | PHOTOCHROMIC DYES; ISOMERIZATION; SPIROPYRAN; RACEMIZATION; BARRIERS; barriers to ring opening; H-1-NMR temperature-dependent; H-1-NMR time-dependent; merocyanine; spiro-2H-1-benzopyran |
| 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: | 29 Nov 2022 11:43 |
| Last Modified: | 29 Nov 2022 11:43 |
| URI: | https://pred.uni-regensburg.de/id/eprint/48639 |
Actions (login required)
 |
View Item |
