Couplings Deuterium exchange

Imtdazo[4,5-c]pyridtne, 4,5,6,7-tetrahydro-synthesis, 5, 623, 640, 641 Imidazo[4,5-c]pyridine-6-carboxylic acid, 4,5,6,7-tetrahydro-synthesis, 5, 623, 641 Imidazopyridines as anthelmintic, 1, 202 synthesis, 5, 462 Imidazo[l,2-n]pyridines deuterium exchange, 5, 611 diazo coupling, 5, 614 Dimroth rearrangement, 5, 613 halogenation, 5, 611 hydrogenation, 5, 614 Mannich reaction, 5, 612 nitration, 5, 612 1-oxides... 

Conditions (003)280, 25 °C, 400 and 600 MHz ( //), 100 MHz ( C). (a) HH COSY plot (600 MHz) following D2O exchange (b) H NMR spectra before and after deuterium exchange (c) sections of the C NMR spectra, in each case with the H broadband decoupled spectrum below and NOE enhanced coupled spectrum (gated decoupled) above ... 

The above considerations do not necessarily apply to reactions of electrophilic reagents with pyrazole and imidazole anions (134, 135). The imidazole anion is sometimes (diazo coupling, halogenation, deuterium exchange) substituted in the 2-position (139) and the indazole anion in the 3-position (cf. Section 3.4.1.4.5). 

Buckingham theory and, 330 chain decomposition, 325 cooperative behavior of defects, 338 deuterium shifts, 361 dispersive interactions, 330 elastic strain, 333 electrostatic coupling, 352 exchange of positions, 351 heteroisotopic pairs, 348... 

Nassar, A. E. (2003). Online hydrogen-deuterium exchange and a tandem-quadrupole time-of-flight mass spectrometer coupled with liquid chromatography for metabolite identification in drug metabolism. J. Chromatogr. Sci. 41 398-404. 

Recent experimental developments in coupling IR spectroscopy techniques with mass spectrometry, which allow the structural characterization of isolated and microsolvated protonated aromatic molecules in the gas phase have been summarized.64 Hydrogen-deuterium exchange has been observed at Ha in (59) and some closely related substrates when this ligand is complexed to Cu1 in [2Hg]acetone.65 The process is finely controlled by the precise coordination distance required to form agostic interaction between Cu(I) and the C-H bond and is believed to involve the enol form of [2H6]acetone and a reversible Cu(I) to Cu(III) interconversion. 

Unsubstituted imidazole reacts with most electrophiles preferentially at C-4(5), but in neutral or basic media it is often difficult to prevent multiple substitution, e.g. halogenation. Deuterium exchange is unusual in that 2-exchange is more facile than 4- or 5-exchange, and diazo coupling occurs with about equal facility in both 2- and 4-positions. Acidic reagents almost always involve the protonated imidazole (imidazolium) as the reactive species. In this form the reactivity is greatly decreased, and 4(5)-substitution is observed, e.g. nitration and sulfonation. Friedel-Crafts reactions will not occur at all. Under severe conditions, disubstitution may be possible. 

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