Issue 5, 1998

Further insight via15N NMR spectroscopy into the reactive intermediates formed by superacid protonation of crowded nitro-PAHs: persistent dihydroxyiminiumpyrenium and hydroxyiminiumpyrenium dications

Abstract

Low temperature protonation of 1-nitropyrene and its 15N-labelled isotopomer with FSO3H·SbF5 (1∶1) (‘magic acid’)–SO2ClF (or SO2) or with FSO3H·SbF5 (4∶1)–SO2ClF generates either the dihydroxyiminiumpyrenium dication (NO2 diprotonation) or the hydroxyiminiumpyrenium dication as the principle NMR observable persistent species (depending on the sample concentration, reaction time and the superacid). The latter is independently generated by diprotonation of authentic 1-nitrosopyrene. Variable formation of dihydroxyiminiumpyrenium and hydroxyiminiumpyrenium dications is also observed in the protonation of sterically crowded 1-nitro-2,7-di-tert-butylpyrene, which gives the corresponding dihydroxyiminiumpyrenium dication in FSO3H·SbF5 (1∶1)–SO2ClF (or SO2) and the hydroxyiminiumpyrenium dication by low temperature reaction with FSO3H·SO2ClF or CF3SO3H·SO2. Protonation of the buttressed 1-nitro-2,4,6,8,10-pentaisopropylpyrene and its 15N-labelled isotopomer produces the dihydroxyiminiumpyrenium dication (no NMR evidence for the formation of the hydroxyiminiumpyrenium dication) which, as shown before (J. Chem. Soc., Perkin Trans. 2, 1995, 537), undergoes a facile cyclization to the oxazoline-fused pyrenium cation for which 15N NMR data are now presented. Diprotonation and subsequent cyclization of the singly 15N-labelled 1,3-dinitro-2,4,6,8,10-pentaisopropylpyrene are also studied. Whereas our work reaffirms the generality of NO2 diprotonation in nitropyrenes, it focuses attention on an additional pathway leading to [double bond, length half m-dash]NH(OH) dication formation.

PM3 calculations are used as a complementary tool to examine the geometries and energies of the resulting dications.

Article information

Article type
Paper

J. Chem. Soc., Perkin Trans. 2, 1998, 1167-1172

Further insight via15N NMR spectroscopy into the reactive intermediates formed by superacid protonation of crowded nitro-PAHs: persistent dihydroxyiminiumpyrenium and hydroxyiminiumpyrenium dications

K. K. Laali and P. Erik Hansen, J. Chem. Soc., Perkin Trans. 2, 1998, 1167 DOI: 10.1039/A800208H

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Spotlight

Advertisements