Cryoscopic measurement

Isoxazole dissolves in approximately six volumes of water at ordinary temperature and gives an azeotropic mixture, b.p. 88.5 °C. From surface tension and density measurements of isoxazole and its methyl derivatives, isoxazoles with an unsubstituted 3-position behave differently from their isomers. The solubility curves in water for the same compounds also show characteristic differences in connection with the presence of a substituent in the 3-position (62HC(17)1, p. 178). These results have been interpreted in terms of an enhanced capacity for intermolecular association with 3-unsubstituted isoxazoles as represented by (9). Cryoscopic measurements in benzene support this hypothesis and establish the following order for the associative capacity of isoxazoles isoxazole, 5-Me, 4-Me, 4,5-(Me)2 3-Me> 3,4-(Me)2 3,5-(Me)2 and 3,4,5-(Me)3 isoxazole are practically devoid of associative capacity. 

The existence of the nitronium ion in sulfuric-nitric acid mixtures was demonstrated both by cryoscopic measurements and by spectroscopy. An increase in the strong acid concentration increases the rate of reaction by shifting the equilibrium of step 1 to the right. Addition of a nitrate salt has the opposite effect by suppressing the preequilibrium dissociation of nitric acid. It is possible to prepare crystalline salts of nitronium ions, such as nitronium tetrafluoroborate. Solutions of these salts in organic solvents rapidly nitrate aromatic compounds. ... 

For water at 0°C (the osmotic coefficient is mostly determined from cryoscopic measurements),... 

Fig. 2. The proposed solution structure as determined by cryoscopic measurements.

E. NMR Spectroscopic and Cryoscopic Measurements 1. Li20-, Na20-, and Fluoride-Complexed Clusters... 

Cryoscopic measurements in benzene with different concentrations have demonstrated that the compounds remain undissociated. However, 8 and 9 undergo dissociation in solution as shown by means of NMR and cryoscopic measurements. A relatively strong deshielding of the 7Li nuclei has been observed for 8 and 9 but also in the case of the incompletely lithiated clusters 3a and 4a. 

The dimer 12 can only be dissolved in ether solvents, when it undergoes dissociation, as corroborated by cryoscopic measurements and 23Na NMR spectra (24). In contrast, the Narduster salt 14 cannot be dissolved in any common organic solvents without decomposition... 

The question as to the best formulation of structures and species in some binary fluoride systems was the subject of extensive experimental investigations, involving infrared and Raman spectroscopy in the molten state and in solutions as well as NMR spectroscopy and conductometric and cryoscopic measurements. Some crystal structure studies have also been published. The systems of SeF4 with BF3, SbF5, AsF5, NbF5, and TaFs have been studied recently. 

The final conductivity of the Ph3 PO system is lower than that of the Ph2POCl system, although the former is known to have a higher donicity than the latter. Cryoscopic measurements in the Ph2POCl system reveal that the number of particles is increased by the ionization process and thus autocomplex formation can be excluded. The following mode of ion formation has been suggested ... 

The solution structures of cyano-Gilman cuprates and lower-order cyanocuprates have been studied by cryoscopic measurements in THF [141]. The results of this study have in several cases shown ways to obtain useful single crystals of several higher- and lower-order cyanocuprates and consequently to determine their structures in the solid state. It appears that a number of these cyanocuprates retain their observed solid-state structure when dissolved in THF. 

All these transformations except for reversion of radical to cation have been accomplished with the benzobisdithiazolium cation (60) which has given rise to radical cation (61) and diradical (62) <86SM233,86SM239,88JCR(S)358>. The diradical (62) is a dimer in solution (cryoscopical measurements in hexane) <86SM233> the radical cation (61) is loosely dimeric in the crystal (Section 4.12.3.1). 

Crown thioethers, coordination chemistry, 35 3 (CIO4), 43 226 Crude oil, vanadium in, 35 99 Crustaceans, arsenic in, 44 150, 167, 168, 170 Cryoscopic measurements, sulfuric acid and, 1 390-391... 

The second problem results from the fact that the azaenolates exist as aggregates or mixed aggregates in ethereal solvents. Cryoscopic measurements established that the azaenolate generated from 4,5-dihydro-4-methoxymethyl-2-methyl-5-phenyloxazole and butyllithium in tetrahydrofuran is a dimer18. When the metalation was performed with butyllithium or tert-butyl-lithium, an aging effect was observed. Thus, the enantiomeric excess on alkylation drops from 43% to 28% and 11 % when the azaenolates generated at — 78 °C were allowed to warm to... 

Due to disorder in the cyclopentadienyl groups the exact bonding of the cyclopentadienyl group to zinc remained uncertain, but it has been suggested that the cyclopentadienyl group is /7 -bonded to one zinc atom and r -bonded to the other one. In solution, however, cryoscopic measurements in benzene pointed to the existence of discrete monomeric species. IR and H NMR studies of solutions of 57 are consistent with /j -binding of the cyclopentadienyl group to zinc in a symmetric Csy structure. 

TABLE 3 DETERMINATION OF ASSOCIATION NUMBER OF BPMg BY CRYOSCOPIC MEASUREMENTS IN BENZENE SOLUTION. 

Concentration of BPMg calculated from U.V. spectra xlf)2 mol.kg-1 Concentration of BPMg calculated from cryoscopic measurements 10 mol.kg l Association number a ... 

The theoretical mol. wt. for H5IO6 is 227 96. The ebulliscope measurements show that the acid is probably ionized like a binary electrolyte H5I06=H-+H4l06 in boiling aq. soln., while the cryoscopic measurements of the 5 per cent. soln. show that the ionization is not so very marked, and becomes very small with the 12 to 20 per cent. soln. Taken in conjunction with the conductivity measurements, these results are taken to show that polymerized molecules are probably present in the cold soln. This conclusion is in accord with the results obtained with telluric acid. 

Sulphur, however, dissolves in certain organic liquids, for example, hot glycerol or ethylene glycol, and in pyrosulphuric aeid, yielding clear blue solutions.5 Cryoscopic measurements with solutions in the latter solvent indicate that the sulphur molecules are diatomic, and it is to be assumed that this is also the case with the blue solutions in organic solvents. Thus, in such solutions the sulphur is more highly dispersed than in most organic solvents, in which the molecules are octatomic. 

Sulphur Monobromide, or Disulphur Dibromide, S2Br2.—This is the only definite bromide of sulphur. It is obtained on heating an equi-atomic mixture of sulphur and bromine at 100° C. in a sealed tube.4 The product is distilled under reduced pressure and collected in a dry receiver. Combination of the two elements can also occur at a lower temperature, as is shown by the fact that sulphur dissolved in bromine is present as sulphur monobromide molecules and not as free sulphur, proof being possible by cryoscopic measurements.5... 

Confirmatory evidence of the probable correctness of the formula Na2Sa04 is supplied by electrical conductivity measurements on aqueous solutions and comparison of the results with those given by the normal salts of the other sulphur oxy-acids, namely Na2S04, Na2S03, Na2S203 and NajSa-Og. All these salts dissociate in two stages. Cryoscopic measurements with the sodium salt also indicate the formation of three ions per molecule. 

Cryoscopic measurements on the acid in benzene, etc., indicate a mixture of single and double molecules. Single molecules of thiocyanie acid may be represented by the formula NsC — SH or S C=NH. Probably the inorganic salts and the esters derived from them have the constitution represented by the first formula. The esters are converted into sulphonic acids and hydrocyanic acid by oxidation,... 

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