- THE DIPOLE MOMENTS OF 1,3-DIMETHYLTHIOUREA, 1,3-DIMETHYL-2-CYANOGUANIDINE AND 1,1-BIS-METHYLAMINO-2-NITROETHENE IN AQUEOUS SOLUTION
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The dipole moments, ν, of 1,3-dimethylthiourea, 1,3-dimethyl-2-cyanoguanidine and 1,1-bis-methylamino-2-nitroethene which are important partial structures of histamine H2 receptor antagonist drugs have been determined in aqueous solution at 25 deg C from static permittivities measured over a wide frequency range.The dipole moments were respectively 10.0, 13.1 and 15.1 Debyes, suggesting that each compound has a high degree of zwitterionic character in water.
- Young, Rodney C.,Ganellin, C. Robin,Graham, Michael J.,Grant, Edward H.
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p. 1493 - 1498
(2007/10/02)
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- MECHANISM OF H/D EXCHANGE AND VINYLIC SUBSTITUTION IN 2,2-DISUBSTITUTED NITROETHYLENE AND RELATED STUDIES
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Rate measurements for H/D exchange at the α-C atom of the nitroethylenic moiety in ranitidine, 2 (a histaminic H2-receptor antagonist with ulcerostatic activity), and in the model compounds 3a, 3b have revealed pseudo-first order, pH-dependent kinetics.These data have been interpreted in terms of an acid-catalysed intramolecular proton (deuterium) transfer within the nitrolic form of the compounds investigated with inversion of configuration at the carbon-carbon double bond.Qualitative studies of the rates of nucleophilic substitution at the vinylic β-C atom in 2,2-bismethylthio-1-nitroethylene (3a) and 2,2-bismethylthio-N-cyanoazomethine (4a) with methylamine, revealed inversion of the relative rates of the first and second substitution step.The result has been rationalized as due to a change from addition-elimination to β,γ-elimination-addition mechanism.HMO calculations of the ?-electron densities and ?-bond orders in 3a-3c and 4a-4c support this rationalization.
- Sega, Alessandro,Toso, Roberto,Sunjic, Vitomir,Klasinc, Leo,Sabljic, Aleksandar,Srzic, Dunja
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p. 217 - 222
(2007/10/02)
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