Melting point, experimental

FIGURE 2.2 n-Paraffin melting points experimental and calculated data. 

Both the amount and randomness of branching affect the melting point. Experimental conditions used for the following data were not adequate for equilibrium crystallinity and accuracy of melting points (52). 

An extensive series of studies for the prediction of aqueous solubility has been reported in the literature, as summarized by Lipinski et al. [15] and jorgensen and Duffy [16]. These methods can be categorized into three types 1 correlation of solubility with experimentally determined physicochemical properties such as melting point and molecular volume 2) estimation of solubility by group contribution methods and 3) correlation of solubility with descriptors derived from the molecular structure by computational methods. The third approach has been proven to be particularly successful for the prediction of solubility because it does not need experimental descriptors and can therefore be applied to collections of virtual compounds also. 

It is remarkable that only two descriptors were needed in this method. However, this equation is mostly only of historical interest as it is of little use in modem dmg and combinatorial library design because it requires a knowledge of the compound s experimental melting point which is not available for virtual compounds. Several methods exist for estimating log P [1-14], but only a few inroads have been made into the estimation of melting points. The melting point is a key index of the cohesive interactions in the solid and is still difficult to estimate. 

Full experimental details for the determination of melting and boiling points are given in Sections 11,10 and 11,11 respectively. The Tables II, 9, A and II, 9, B list suitable substances for the cabbration of thermometers by melting point or boiling point determinations respectively. Substances which are bracketed are alternative to each other. It need hardly be emphasised that only compounds of the highest purity should be employed. 

The student should read Sections 1,10 to 1,16 carefully before commencing any experimental work. A supply of melting point capillaries is prepared as described in Section 11,10 (compare Fig. 77, R , I). The apparatus illustrated in Fig. 77. 10, 2, a is assembled with concentrated sulphuric acid as the bath liquid the thermometer selected should have a small bulb. The melting points of pure samples of the following compounds are determined in the manner detailed in Section 11,10 —... 

Drop 1 g. of sodium into 10 ml. of ethyl alcohol in a small flask provided with a small water condenser heat the mixture until all the sodium has dissolved. Cool, and add 1 g. of the ester and 0-5 ml. of water. Frequently the sodium salt of the acid will be deposited either at once or after boiling for a few minutes. If this occurs, filter oflF the solid at once, wash it with a little absolute ethyl alcohol (or absolute methylated spirit), and convert it into the p-bromophenacyl ester, p-nitro-benzyl ester or S-benzyl-tso-thiuronium salt (for experimental details, see Section 111,85). If no solid separates, continue the boiling for 30-60 minutes, boil oflF the alcohol, allow to cool, render the product just neutral to phenolphthalein with dilute sulphuric or hydrochloric acid, convert the sodium salt present in solution into a crystalline derivative (Section 111,85), and determine its melting point. 

Derivatives of higher melting point may be obtained withp-nitrobenzoyl chloride the experimental details are similar to those given above for benzoyl chloride. 3 5-Dinitrobenzoyl chloride (Section 111,27,7) may also be used glycerol gives unsatisfactory results with this reagent. 

The normal boiling point of 2-methylthiazole is 17 0= 128.488 0.005°C. The purity of various thiazoles was determined cryometrically by Handley et al. (292), who measured the precise melting point of thiazole and its monomethyl derivatives. Meyer et al. (293, 294) extended this study and, from the experimental diagrams of crystallization (temperature/degree of crystallization), obtained the true temperatures of crystallization and molar enthalpies of fusion of ideally pure thiazoles (Table 1-43). 

Prepa.ra.tlon, There are several methods described in the Hterature using various cobalt catalysts to prepare syndiotactic polybutadiene (29—41). Many of these methods have been experimentally verified others, for example, soluble organoaluminum compounds with cobalt compounds, are difficult to reproduce (30). A cobalt compound coupled with triphenylphosphine aluminum alkyls water complex was reported byJapan Synthetic Rubber Co., Ltd. (fSR) to give a low melting point (T = 75-90° C), low crystallinity (20—30%) syndiotactic polybutadiene (32). This polymer is commercially available. 

A furtlier empiiical expression, due to Andrade, for die viscosity of liquid metals at tlreir melting points, which agrees well with experimental data is... 

For materials with very low melting points it is sometimes convenient to use dilute solutions in acetone, methanol, pentane, diethyl ether or CHCI3-CCI4. The solutions are cooled to -78° in a dry-ice/acetone bath, to give a slurry which is filtered off through a precooled Buchner funnel. Experimental details, as applied to the purification of nitromethane, are given by Parrett and Sun [J Chem Educ 54 448 7977]. 

This table shows that the similarity of the two aglycones is most marked in their salts, but they do not appear to be dimorphic forms giving identical salts, for the melting-points of the bases are unchanged after sublimation, the rotations of the two bases in solution are different, though those of the two hydrochlorides are identical within the limits of experimental error, and all attempts at interconversion of the two bases... 

CNTs, or changes of structure or melting point of liquid in nanometric cavities, etc. Many interesting experimental and theoretical studies are in progress on the CNT filling, and the obtained new knowledge will not only be useful for fullerene-related materials field, but also it will illuminate the development of the whole field of nanotechnologies. 

Polypropylene made by free-radical polymerization is generally atactic , that is to say, there is no pattern to the stereochemistry. On the other hand, both isotactic polypropylene (in which all the stereocenters are the same) and syndiotactic polypropylene (in which the stereocenters alternate) may be made via the Ziegler-Natta process (see Chapter 18, Problem 4). Experimentally, both isotactic and syndiotactic polypropylene generally have higher melting points than atactic polypropylene. 

The data for our analysis were collected from production runs of about 10000 steps, corresponding to a total simulation time of approximately 2 ps. The temperature for each simulation was chosen as that value for which experimental data are available. In general, the temperature lies about 50 K above the corresponding melting point. A detailed description of the computational features and the simulation procedure -including systems and temperatures - is given in [7]. 

The influence of surface energy on the melting-point of a solid has been calculated by P. Pawlow, who found experimentally that with salol granules of surfaces 228—1296 p2, the m.pt. decreased 2 8° C. per 100 times increase of surface (p = 0 001 mm.). 

Kirchhoffs investigation does not show that the sublimation and evaporation curves meet each other at the temperature at which solid and liquid are in equilibrium with vapour it proves that they are inclined at an angle, but the further fact that they intersect requires separate proof, which was inferred by James Thomson, and experimentally demonstrated by Ferche (1891) in the case of benzene the point of intersection, calculated from the vapour-pressure curves, was 5 405° C, whereas the melting-point was 5 42° C. 

That this is not the case follows from the experimental data discussed by A. Russell (9), and F. Koref (10) has attempted to calculate the change of frequency of an element when it enters into combination by means of the alteration of melting-point and atomic volume. According to Lindemann s equation, for the combined atom ... 

The change of melting-point can produce a very marked alteration of v (e.g., carbon and carbon dioxide). Koref calculates the v values for a number of compounds, and the molecular heats thence obtained agree with the experimental values moderately well. 

If 31/1 is small and AF is a known function of temperature, Eq. (2.3) can be used to determine the melting point and surface free energy of a lamella from experimental data. For long chain molecules there are several difficulties in choosing the relevant form for AF, Therefore we first consider the limiting case... 

The theory of melting continues to be the subject of recent publications, including consideration of vacancy concentrations near the melting point [8,9], lattice vibrations and expansions [8,10—12], Meanwhile, the phenomenon also continues to be the subject of experimental investigations Coker et al. [13], from studies of the fusion of tetra-n-amyl ammonium thiocyanate, identify the greatest structural change as that which... 

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