Hoff studies

While Arrhenius was studying conductivity, others were characterizing colligative properties of solutions. The Dutch chemist J. T. van t Hoff studied osmotic pressure and derived the law of osmotic pressure,... 

This term was introduced to the normal chemical language in the 20th century due to the efforts of Bodenstein. In Semenov s view, the understanding that, no matter how complicated is a reaction s process the law of the elementary act is sufficiently simple, is exclusively the credit "of Van t Hoff s genius prediction, though he himself did not understand it quite clearly [5, p. 6]. Though the epithet "genius with respect to Jacob Henri Van t Hoff is still valid, the situation, however, defies its complete reconstruction. On the one hand, it is likely that Van t Hoff renounced in principle the analysis of complex reactions that do not obey the laws of "normal conversions . Apparently, it is for this reason that in the "Etudes he did not examine etherification reactions practically [19]. Van t Hoff studied such simple reactions as the decomposition of dibromosuccinic acid and the reaction of... 

J. H. van t Hoff, Studies in Chemical Dynamics, (trans. T. Ewan), F. Muller, Amsterdam, with Williams and Norgate, London, 1896. 

Two compounds from this list are worthy of note lactic acid (Fig. 10) and tartaric acid (Fig, 11). Wishcenus (Fig. 12) extensively investigated the isomers of lactic add between 1863 and 1873, and was convinced that the number of isomers exceeded that allowed by the existing structural theory (12). However, due to experimental difficulties in obtaining pure samples of the isomers, in addition to the limits of the structural theory then known to him, he ended up going around in drdes. van t Hoff studied the publications of WisUcenus on lactic adds and they led him to his own stereochemical ideas. In fact, lactic add was the first concrete example of an optically active compound that van t Hoff discussed after his theoretical introduction. He pointed out that ethylidene lactic add contains an asymmetric carbon. Therefore, it can exist as two pure enantiomers ora racemic mixture, which nicely cleared up the confusion surrounding the lactic add... 

Van t Hoff had studied science and mathematics at the Delft Polytechnic, then the University of Leiden. Eager for the best chemical education possible, he entered Kekul s lab in Bonn in October 1872 and worked there until June 1873. He must have become acquainted there with Kekule s tetrahedral carbon models, which Kekule was using regularly in his lectures. In summer and fall 1873 van t Hoff studied at Utrecht, passing his doctoral exams a few days before the end of the calendar year. He then spent from January until June 1874 with Wurtz... 

A connnon approach has been to measure the equilibrium constant, K, for these reactions as a fiinction of temperature with the use of a variable temperature high pressure ion source (see section (Bl.7.2)1. The ion concentrations are approximated by their abundance in the mass spectrum, while the neutral concentrations are known from the sample mlet pressure. A van t Hoff plot of In K versus /T should yield a straight Ime with slope equal to the reaction enthalpy (figure B1.7.11). Combining the PA with a value for basicityG at one temperature yields a value for A.S for the half-reaction involving addition of a proton to a species. While quadnipoles have been tire instruments of choice for many of these studies, other mass spectrometers can act as suitable detectors [19, 20]. 

Amino-4-phenylthiazole when heated with Raney Ni is reported to yield acetophenone (469). In the course of a general study on reductive cleavage in heterocyclic systems Hoff et al. studied the reaction of 2-amino-4-methylthiazole with Na in liquid ammonia. Two equivalents of Na are necessary to obtain a mixture of 4-methyl-3-thiazoline (240) and... 

As already mentioned, there are two so called "dead volumes" that are important in both theoretical studies and practical chromatographic measurements, namely, the kinetic dead volume and the thermodynamic dead volume. The kinetic dead volume is used to calculate linear mobUe phase velocities and capacity ratios in studies of peak variance. The thermodynamic dead volume is relevant in the collection of retention data and, in particular, data for constructing vant Hoff curves. 

Panagiotopoulos et al. [16] studied only a few ideal LJ mixtures, since their main objective was only to demonstrate the accuracy of the method. Murad et al. [17] have recently studied a wide range of ideal and nonideal LJ mixtures, and compared results obtained for osmotic pressure with the van t Hoff [17a] and other equations. Results for a wide range of other properties such as solvent exchange, chemical potentials and activity coefficients [18] were compared with the van der Waals 1 (vdWl) fluid approximation [19]. The vdWl theory replaces the mixture by one fictitious pure liquid with judiciously chosen potential parameters. It is defined for potentials with only two parameters, see Ref. 19. A summary of their most important conclusions include ... 

Hoff (1983) studied the effect of igniting natural gas after a simulated pipeline rupture by firing a bullet into the gas mixture. The tests were on a 10-cm diameter pipeline operating at an initial pressure of 60 bar and a gas throughput of 400,000 mVday. The openings created in the pipeline simulated full-bore ruptures. Maximum flame speeds of approximately 15 m/s, and maximum overpressures of 1.5 mbar were measured at a distance of 50 m. 

Hoff, A. B. M. 1983. An experimental study of the ignition of natural gas in a simulated pipeline rupture. Comb, and Flame. 49 51-58. 

Oxidation of arsenic(III) by chromate in alkaline medium was studied by Kolt-hoff and Fineman. They found the reaction to be first order with respect to both chromate and arsenic(rir). At pH greater then 9.1 the rate coefficient is independent of the hydrogen-ion concentration. The average value of the rate coefficient at 30° in solutions of pH 9.1 and ionic strength 1.75 was found to be (1.61+0.08) x 10 l.mole sec . ... 

Of great importance for the development of solution theory were the studies of col-ligative solution properties, detected in the 1870s and 1880s by F. M. Raoult, J. H. van t Hoff, and others. These are properties that depend not on the chemical nature of solutes but on their concentration. Three such colligative properties exist ... 

Equilibrium measurements measure the relative AG, and thermochemical studies generally are interested in enthalpy values, AH. The enthalpy can be obtained from AG by using the relation AG = AH — TAS. The entropy of proton transfer can either be estimated, reliably calculated using electronic structure calculations, or can be measured directly by using a Van t Hoff approach. Measuring the quantity AS requires a variable temperature study. 

Since the experimental studies of van t Hoff at the turn of the century, geochemists have sought a quantitative basis for describing the chemical evolution of seawater and other complex natural waters, including the minerals that precipitate from them, as they evaporate. The interest has stemmed in large part from a desire to understand the origins of ancient deposits of evaporite minerals, a goal that remains mostly unfulfilled (Hardie, 1991). 

Within this historical setting, the actual birth of stereochemistry can be dated to independent publications by J. H. van t Hoff and J. A. Le Bel within a few months of each other in 1874. Both scientists suggested a three-dimensional orientation of atoms based on two central assumptions. They assumed that the four bonds attached to a carbon atom were oriented tetrahedrally and that there was a correlation between the spatial arrangement of the four bonds and the properties of molecules, van t Hoff and Le Bell proposed that the tetrahedral model for carbon was the cause of molecular dissymmetry and optical rotation. By arguing that optical activity in a substance was an indication of molecular chirality, they laid the foundation for the study of intramolecular and intermolecular chirality. 

Examples of other work on research schools M. Eckert, "Sommerfeld s School and the Electron Theory of Metals," HSPS 17 (1987) 191234 Gerald Geison, Michael Foster and the Cambridge School of Physiology The Scientific Enterprise in Late Victorian Society (Princeton Princeton University Press, 1978) L. J. Klosterman, "A Research School of Chemistry in the Nineteenth Century Jean Baptiste Dumas and His Research Students," Annals of Science 43 (1985) 180 H. A. M. Snelders, "J. H. van t Hoffs Research School in Amsterdam (18771895)," Janus 71 (1984) 130 F. L. Holmes, "The Formation of the Munich School of Metabolism," in William Coleman and F. L. Holmes, eds., The Investigative Enterprise Studies on Nineteenth-Century Physiology and Medicine (Berkeley, Los Angeles, and London University of California Press, 1988). 

Ingold quickly found a valuable colleague in H. M. Dawson, who had studied at Manchester with Arthur Smithells and in Germany with van t Hoff, K. Elbs, and Abegg. Thermodynamics and kinetics were Dawson s principal interests "Dawson taught me a lot of physical chemistry in a quiet way, and I became very interested in his attempts to sort out the kinetic effects of the constitutents of electrolytic solutions," Ingold later reminisced. 15... 

Isotopes were not available in van t Hoff s day. My student generation was taught that an asymmetric carbon atom was a carbon atom attached to 4 chemically different groups. When isotopes of carbon, UC and 13C, were first applied as tracers to study carbohydrate metabolism, the entire emphasis was on the chemical similarity of 11C and 13C to the more abundant isotope 12C. Thus, it was of pressing interest to determine whether CO 2 participated in the oxidation of carbohydrate in animal tissues, a conclusion strongly suggested by the demonstration in Krebs laboratory, that pyruvate and oxalacetate behaved alike in pigeon liver, and by Wood and Werkman s earlier demonstration that some he-... 

A van t Hoff plot of In k against l/T yields a straight line if the stationary phase is not deformed. The relation Ink and —AH/RT is used to study the temperature-dependent selectivity of the stationary phase.33-35... 

An interesting historic parallel (91) can be drawn to van t Hoffs proposal of the tetrahedrd geometry for groups bound to a tetra-valent carbon atom because its original appearance was also in the form of an obscure pamphlet in Dutch (Utrecht, 1874) however, van t Hoffs work was quickly translated into French (1875) and German (1876) for publication in vehicles having considerably wider circulation. In Zeelen s case, only the synthetic aspects of his dissertation were subsequently published in the journal literature (92). However, the later paper does provide a cautionary note that the surfactant compounds employed in the film balance studies may not have been optically pure because racemization during their synthesis was possible. 

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