Application of the Variable Oxygen Probe to Determine the π-Electron Donor Ability of the Alkyne Group

Eight ester and ether derivatives of propargyl alcohol with varying electron demand were structurally characterised using low temperature X-ray crystallography, these were combined with seven derivatives obtained from the Cambridge Structural Database. Variable oxygen probe analysis of these derivatives provided evidence that the ethynyl substituent is a relatively weak π-electron donor, and is a slightly less effective donor than the C–C bond of an ethyl substituent.

Experimental evaluation of the electron donor ability of a gold phosphine fragment in a gold carbene complex

Bond length deformations within the cyclopropyl ring of a gold cyclopropyl(methoxy)carbene complex provide an experimental measure of the electron donor ability of the gold phosphine fragment.

Effects of Core and/or Peripheral Protonation ofmeso-Tetra(2-, 3-, and 4-pyridyl)Porphyrin andmeso-Tetra(3-methylpyridyl)Porphyrin on Their UV-vis Spectra

Core and/or peripheral protonation ofmeso-tetra(pyridyl)porphyrins, H2(py)P, with weak and strong acids have been studied by UV-vis spectroscopy. The results support the proposal that the position of the Soret as well as the Q(0,0) bands of the dications is influenced byπdonation from themesosubstituents to the porphyrin core. The red shift of the Q(0,0) band of H2t(py)P dications with 2-, 3-, and 4-pyridyl substituents does not correlate with the order ofπelectron donor ability of themesogroups. The decreased electron donation from the central nitrogen atoms to the acids on going from 3-pyridyl group to 4- and 2-pyridyl ones has been used to explain this observation. In spite of the negative effect of N-methylation of pyridyl substituents on the basicity of the central nitrogen atoms ofmeso-tetra(3-methylpyridyl)porphyrin, H2t(3-Mepy)P, protonation of H2t(3-Mepy)P occurs with weak and strong acids. The blue shift of the Q(0,0) bands upon protonation of H2t(3-Mepy)P with weak and strong acids clearly shows the importance of resonance interactions between theπ-systems of porphyrin and the aryl substituents on the position of the band.

DDQ-promoted thiocyanation of aromatic and heteroaromatic compounds

Thiocyanation of various aromatic and heteroaromatic compounds has been achieved using ammonium thiocyanate in the presence of 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) in methanol solution at room temperature and under reflux condition. The rate of reaction is influenced by the electron-donor ability of the aromatic nucleus.Key words: amines, DDQ, indoles, thiocyanation.