1986-00-1Relevant articles and documents
A new type of excited-state intramolecular proton transfer: Proton transfer from phenol OH to a carbon atom of an aromatic ring observed for 2-phenylphenol
Lukeman, Matthew,Wan, Peter
, p. 9458 - 9464 (2002)
The photochemical deuterium incorporation at the 2′-and 4′-positions of 2-phenylphenol (4) and equivalent positions of related compounds has been studied in D2O (CH3OD)-CH3CN solutions with varying D2O (CH3OD) content. Predominant exchange was observed at the 2′-position with an efficiency that is independent of D2O (MeOD) content. Exchange at the 2′-position (but not at the 4′-position) was also observed when crystalline samples of 4-OD were irradiated. Data are presented consistent with a mechanism of exchange that involves excited-state intramolecular proton transfer (ESIPT) from the phenol to the 2′-carbon position of the benzene ring not containing the phenol, to generate the corresponding keto tautomer (an o-quinone methide). This is the first explicit example of a new class of ESIPT in which an acidic phenolic proton is transferred to an sp2-hybridized carbon of an aromatic ring. The complete lack of exchange observed for related substrates 6-9 and for planar 4-hydroxyfluorene (10) is consistent with a mechanism of ESIPT that requires an initial hydrogen bonding interaction between the phenol proton and the benzene π-system. Similar exchange was observed for 2,2′-biphenol (5), suggesting that this new type of ESIPT is a general reaction for unconstrained 2′-aryl-substituted phenols and other related hydroxyarenes.
Studies of Consecutive Reactions of Quinones in a Reversed Geometry Mass Spectrometer
Proctor, C. J.,Kralj, B.,Larka, E. A.,Porter, C. J.,Maquestiau, A.,Beynon, J. H.
, p. 312 - 322 (2007/10/02)
Consecutive reactions involving the ejection of molecules of carbon monoxide from quinone systems have been studied.Using a reversed geometry double focusing mass spectrometer, the individual steps of a consecutive reaction may be separated into different field free regions.The structure of ions formed in the ion source may be compared with those formed from the fragmentation of metastable ions in a field free region by studying differences in the pattern of translational energies released when they break.In the case of anthraquinone it is found that two structures exist for the +. ion.Critical energy measurements strengthen this argument.Furthermore, 18O labelling has been used to distinguish between the loss of carbon monoxide from different positions on the molecular ion of 1-hydroxyanthraquinone.
