Quantum-chemical calculations (ab initio and semiempirical) were performed for neutral and monoprotonated model compounds of general formula H i X=NH (where X is C, N, S or P and i = 1, 2 or 3) and thermodynamic parameters for the protonation reaction were calculated. All derivatives belong to the family of nitrogen bases. The basicity of H 2 S=NH is larger than that of H 2 C=NH and lower than that of H 3 P=NH, indicating that derivatives with the S=N group can form a 'bridge' between guanidines and phosphazenes in the gas-phase superbasicity scale. The basicity of HN=NH is lower than that of H 2 C=NH. Topological analysis of electron density distributions in H 3 S=NH, H 2 S=NH 2 and two neutral isomers of H 2 S=NH showed significant differences in the properties of critical points on N-and S-protonations. All parameters such as r, laplacian atomic volumes and dipoles and also bond properties are affected on protonation.
SummaryCoupling column liquid chromatography and gas chromatography on-line is becoming more important in analytical chemistry. Especiallywhen large amounts of polar solvents can be introduced into the gas chromatograph without any problem, the technique will offer new possibilities. With a DPTMDS retention gap, evaporation rates and flooded zones of some solvents have been determined. Two modes of operation using partially concurrent solvent evaporation conditions are discussed: (1) injecting a sample via a loop of an LC valve followed by introduction into the gas chromatograph with an LC pump; (2) trace enrichment on a precolumn followed by on-line desorption with n-propanol into the gas chromatograph. Preliminary results for a splitter system, inserted between the retention gap and the analytical column which allows a considerable increase of the evaporation rate are also presented.
SummaryA system is described which accelerates the solvent evaporation rate in the retention gap. The evaporation is due to a saturation effect of the carrier gas stream, and a considerable increase in evaporation rate is obtained by inserting a split outlet between the retention gap and the Capillary separation column in the gas chromatograph. By varying the backpressure of the splitter device, the flow rate through the retention gap can be adjusted and so too the evaporation rate. The evaporation process was monitored by inserting a detector in the split outlet line.The technique was applied to the on-line LC trace enrichmentlGC analysis of water containing a mixture of polycyclic aromatic hydrocarbons.
A series of ortho-substituted NIN1-dimethyl-N2-phenylformamidines (o-FDM P) have been synthesized and their structure determined by i.r. and 'H n.m.r. methods. All, except the hydroxy derivative, have the same structure ( E ) . In the case of the hydroxy derivative an intramolecular hydrogen bond appears, and thus two structures Z (20%) and E (80%) are observed in the 'H n.m.r. spectrum in CDCI,. The influence of the ortho-substituent on the retention indices, determined on a non-polar column, and on the pK, values, measured in 95.6% ethanol (azeotrope) and in water is discussed, and compared with those observed for meta-and para-derivatives. The retention indices of the ortho-derivatives, except the hydroxy derivative, obey the same linear correlation as meta-, para-, and other alkyl and aralkyl derivatives. A deviation of the pK, values of the ortho-derivatives from the linear correlations found for the meta-and para-derivatives are explained by steric effects of the substituent and medium effects.This paper reports the influence of ortho-substituents on the physicochemical properties of N ' N '-dimethyl-N ,-phenyl-
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