Related Experiment Video
Updated: Aug 19, 2026

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
Inter- and intramolecular excited state proton transfer in 2-hydroxy-9H-carzole-1-carboxylic acid
1Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India.
Abstract:
Absorption, fluorescence and fluorescence excitation spectroscopy and single photon counting time dependence spectrofluorimetry have been used to study the inter- and intramolecular excited state proton transfer (ESIPT) reactions in 2-hydroxy-9H-carbazole-1-carboxylic acid (2-HCA). Except in cyclohexane and water (pH 5) dual fluorescence is observed in rest of the solvents used. Normal Stokes shifted band seems to originate from 2-HCA-1-c and tautomer emission band from the tautomer formed by ESIPT in 2-HCA-1-c followed by structural reorganization. Both these emission band systems originate from the same ground state species. AM1 and CNDO/S-CI calculations have been carried out to establish the identity of the species. Different prototropic equilibria have been determined and discussed.
Related Concept Videos
Reactions of Carboxylic Acids: Introduction
Loss of Carboxy Group as CO2: Decarboxylation of β-Ketoacids
Intramolecular Aldol Reaction
Structures of Carboxylic Acid Derivatives
Carboxylic acid derivatives contain an acyl group attached to a heteroatom such as chlorine, oxygen, or nitrogen. The carbonyl carbon and oxygen are both sp2-hybridized with an unhybridized p orbital.
The three sp2 orbitals of the carbonyl carbon form three σ bonds, one each with the carbonyl oxygen, the α carbon, and the heteroatom, whereas the other two sp2 orbitals of the carbonyl oxygen are occupied by the lone pairs. Further, the unhybridized p...
Carbocations
Nitriles to Carboxylic Acids: Hydrolysis

