Application of 4-Hydroxy-, 4-Oxo-, and 4-Hydroxyimino Derivatives of Stable 2,2,6,6-Tetramethylpiperidine N-Oxyl Radical for the Measurements of Lewis Acidity of Solvents

• Autorzy: Głowacka J. , Szczepek W. J. , Wrona P. K.
• Języki publikacji: EN

Abstrakty

EN

UV-VIS spectra of 2,2,6,6-tetramethylpiperidine N-oxyl (TMPNO) stable radical measured in 18 solvents were compared with the spectra of its derivatives functionalized in the 4 position (4-hydroxy- (h-TMPNO), 4-oxo- (o-TMPNO) and 4-hydroxyimino- (i-TMPNO)). The results obtained proved, that the max values corresponding to the n * transition in the N–O chromophore are for all TMPNO derivatives intercorrelated, and they also correlate very well with other acidity parameters (Z, ET and AN). Thus, all these compounds could be used as standard bases for determination of the experimental acidity of solvents. Detailed analysis of the spectral characteristics of all compounds leads to the conclusion, that the molar absorptivities ( ) ofTMPNOand h-TMPNO corresponding to the n* transition are of the order of 10 dm3 mol–1 cm–1, whereas those of the o-TMPNO and i-TMPNO are two times lower. In the case of the* transition we observed an opposite behaviour – the molar absorptivities ( ) of TMPNO and h-TMPNO are close to 2103 dm3 mol–1 cm–1, whereas those of the oxo and hydroxyimino derivatives are equal to ~4.4103 dm3 mol–1 cm–1. The integral intensities of both bands behave accordingly. These differences were attributed to the formation of the head-to-tail dimers, in which the N–O chromophore interacts with the exocyclic double bond in the 4-position of the piperidine.

• Wydawca: Polskie Towarzystwo Chemiczne
• Czasopismo: Polish Journal of Chemistry
• Rocznik: 2000
• Tom: Vol. 74, nr 9
• Strony: 1341--1341
• Opis fizyczny: –1348, Bibliogr. 19 poz., rys.

Twórcy

autor

Głowacka J.

autor

Szczepek W. J.

autor

Wrona P. K.

• Department of Chemistry, University of Warsaw, 02-093 Warsaw, Pasteura 1, Poland