Melting point homologous series

Their hydrophobicity and their plasticity were appreciated and used for a long time in a wide range of activities. To our knowledge, the first wax to have been exploited is beeswax. Beeswax is produced by various species of bees in the world, and it has a melting point between 62°C and 64°C. It mainly contains homologous series of even-numbered fatty acids (C22 C34, C2 being the predominat compound), odd-numbered ra-alkanes (C2i C33, C27 being the major compound) and even-numbered palmitic esters from C40 to C52 (Tulloch and Hoffman, 1972 Kolattukudy, 1976). Hydroxy esters, diesters and hydroxy diesters also form part of beeswax to a lesser extent. 

Cuy [3], for example, observed that certain physical properties, such as melting points, boiling points, molecular volumes, densities and viscosities, are an alternating function of the number of carbon atoms in any homologous series, in such a manner that if melting points, for instance, are plotted against the number of carbon atoms the curve has a saw-tooth appearance (see Fig. 2.1). 

After the discovery of plutoninm and before elements 95 and 96 were discovered, their existence and properties were predicted. Additionally, chemical and physical properties were predicted to be homologous (similar) to europium (gjEu) and gadolinium ( Gd), located in the rare-earth lanthanide series just above americium (gjAm) and curium ((,jCm) on the periodic table. Once discovered, it was determined that curium is a silvery-white, heavy metal that is chemically more reactive than americium with properties similar to uranium and plutonium. Its melting point is 1,345°C, its boihng point is 1,300°C, and its density is 13.51g/cm. ... 

Estimation of Melting Points As indicated above, the development of structure-rm relationships is not as straightforward as it is for other properties. In the following sections we discuss briefly the estimation of Tm for homologous series and for other sets of structurally related compounds. A GCM designed to estimate Tm for more diverse sets of compounds is introduced. Although not very accurate, the GCM approach may be applicable for the following tasks ... 

As the homologous series is ascended the melting-points of the dichlorides fall and the solubility in organic solvents increases. 

The alcohols (alkanols) form another homologous series with the general formula C H2 +1OH (or R— OH, where R represents an alkyl group). All the alcohols possess an -OH as the functional group. Table 15.2 shows the names and condensed formulae of the first four members along with their melting and boiling points. 

Table 1.1 shows that much of the work has been done on hydrocarbons and, in particular, homologous series. As a result, several very accurate methods are available for estimating the melting points of normal alkanes. For example, Broadhurst (1962) reports errors of less than 0.5°C for paraffins with chain lengths between 44 and 100 carbons. Similarly, Hanson... 

Although these methods have limited applicability, observations made during their development contributed to an understanding of the relationship between melting point and molecular structure. For example, Mills (1885) developed the following equation for the melting points of members of a homologous series ... 

Stable phases in the rare earth oxide systems are tabulated and discussed. New data on the structure of sesquioxides quenched from the melt are reported. The structural interrelations between the A, B, and C type sesquioxides and the fiuorite dioxides are pointed out. The sequences of several intermediate oxides in the CeO, PrO., and TbO, systems are observed to be related to the fluorite structure and the C form sesquioxide with respect to the metal atom positions. A hypothetical homologous series of the general formula Mn02n i, related to the fluorite structure and the A form sesquioxide with a more or less fixed oxygen lattice, is suggested. 

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