Alkane melting points

Alkane melting points. The melting-point curve for w-alkanes with even numbers of carbon atoms is slightly higher than the curve for alkanes with odd numbers of carbons. 

Hydrogen bonding m carboxylic acids raises their melting points and boiling points above those of comparably constituted alkanes alcohols aldehydes and ketones... 

Paraffin wax is macrocrystalline, britde, and is composed of 40—90 wt % normal alkanes, with the remainder C g—isoalkanes and cycloalkanes. Paraffin wax has Httle affinity for oil content fully refined paraffin has less than 1 wt % cmde scale, 1—2 wt %, and slack [64742-61-6] above 2 wt %. Within these classes, the melting point of the wax determines the actual grade, with a range of about 46—71°C. Typical properties of petroleum waxes are listed in Table 3. 

Pentaerythritol with its four primary hydroxyl groups is used for the preparation of tetraesters and presents Httie difficulty except for its high melting point of 263°C, when pure. Pentaerythritol tetraesters are used in aircraft lubes, synthetic drying oils, and alkyds. Esters derived from trimethylo1 alkanes and dipentaerythritol are also used in alkyd resins (qv). Esterification may take place in situ during preparation of the alkyd. 

Matthews-Akgerman The free-volume approach of Hildebrand was shown to be valid for binary, dilute liquid paraffin mixtures (as well as self-diffusion), consisting of solutes from Cg to Cig and solvents of Cg and C o- The term they referred to as the diffusion volume was simply correlated with the critical volume, as = 0.308 V. We can infer from Table 5-15 that this is approximately related to the volume at the melting point as = 0.945 V, . Their correlation was vahd for diffusion of linear alkanes at temperatures up to 300°C and pressures up to 3.45 MPa. Matthews et al. and Erkey and Akger-man completea similar studies of diffusion of alkanes, restricted to /1-hexadecane and /i-octane, respectively, as the solvents. 

Wojtkonski [185] has also reported on three series of melt spinnable thermotropic aromatic-aliphatic polyimines. The polyimines were prepared by reaction of 1,2-bis(4-formylphenoxy) ethane, terephthalaldehyde, or 4,4 -biphenyldicarboxaldehyde, respectively, with l,n-bis(4-amino-3-methylphenoxy) alkanes where n = 1-10, 12, 14, and 16 in dry DMAC containing 5% dry lithium chloride. The polymers decomposed at 400°C, and as the length of the flexible aliphatic segments increased, melting points decreased. Polymers with an odd... 

LLDPE with narrow molecular weight distribution exhibits a lower, a sharper melting point [3], better hot tack and heat seal properties as well as higher clarity and better impact resistance (Fig. 3), tensile strength (Fig. 4) [11], and lower levels of alkane-soluble components. The most distinguishing characteristic of metallocene-based LLDPEs is that they are not restricted by the current immutable property relationships that are... 

Alkanes with long, unbranched chains tend to have higher melting points, boiling points, and enthalpies of vaporization than those of their branched isomers. The difference arises because, compared with unbranched molecules, the atoms of neighboring branched molecules cannot get as close together (Fig. 18.5). As a result, molecules with branched chains have weaker intermolecular forces than their unbranched isomers. 

The C=C group and all four atoms attached to it lie in the same plane and are locked into that arrangement by the resistance to twisting of the TT-bond (Fig. 18.7). Because alkene molecules cannot roll up into a ball as compactly as alkanes or rotate into favorable positions, they cannot pack together as closely as alkanes so alkenes have lower melting points than alkanes of similar molar mass. 

Why do branched-chain alkanes have lower melting points and boiling points than unbranched alkanes with the same number of carbon atoms ... 

The double bond in alkenes makes them more rigid than alkanes. Some of the atoms of alkene molecules are locked into a planar arrangement by the TT-bond hence, they cannot roll up into a ball as compactly as alkanes can. Because they do not pack together as compactly as alkanes do, they have lower boiling and melting points. 

The complexes are solids but are not useful as derivatives, since they melt, with decomposition of the complex, at the melting point of urea. They are useful, however, in separating isomers that would be quite difficult to separate otherwise. Thiourea also forms inclusion compounds though with channels of larger diameter, so that n-alkanes cannot be guests but, for example, 2-bromooctane, cyclohexane, and chloroform readily fit. 

IR and Raman spectroscopic studies on films and powders of PDHS indicate that the hexyl side chains are crystallizing into a hydrocarbon type matrix (40). This is indicated by the presence of a number of sharp characteristic alkane bands which become dramatically broadened above the transition temperature. Similar changes are observed for n-hexane below and above the melting point. CPMAS 29Si NMR studies on PDHS also show that the rotational freedom of the side chains increases markedly above the transition temperature (41,42). All of the spectral evidence... 

X-ray diffraction studies have revealed that alkane chains with an even number of carbon atoms pack more closely in the crystalline state => attractive forces between individual chains are greater and melting points are higher. 

Paraffin waxes are also considered of mineral origin and are obtained from petroleum. The petroleum is distilled and the white colour of the wax is obtained by acid washing and purification. It has a typical melting point between about 47 °C and 64 °C. Its uses include candle making, casting and as a solidifier/stabilizer. The wax is composed of C20 C36 n-alkanes (40 90%), isoalkanes and cycloalkanes. 

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. 

Voiatility sequence for C, compounds (from boiling and melting points) alkane > aide- ... 

A simple spreadsheet, such as Microsoft Excel, can serve as the foundation of a database that has forward and reverse search capabilities. For instance, a table of normal alkanes, together with their densities, boiling points, and melting points, can serve as the starting point. If we want to know all the normal paraffins that boil between 0 and 40 C, all we have to do is to do a sort operation on the boiling-point column and obtain the result that the only paraffin that is in the range is normal heptane with a boiling point of 36.1 °C. For the more advanced Boolean search of normal alkanes that boil between 0 and 40 °C AND melt between —40 and 0 °C, it would be a far more laborious task in a spreadsheet. 

The immiscibility in the liquid phase was observed for [CjoCilm]Cl with water and for [C8Qlm]Cl wifh water and 1-octanol [51]. For both salts the solubility in 1-octanol was higher than that in water. Only [C8Cilm]Cl was liquid at room temperature (melting point, = 285.4 K) [51]. The binary mixtures of [Ci2Cilm]Cl with n-alkanes and ethers have shown a very flat liquidus curve, but only in [C42Cjlm]Cl + n-dodecane, or methyl 1,1-dimeth-ylether] the immiscibility in the liquid phase was observed for the very low solvent mole fraction [95]. 

As with alkanes, the boiling points and melting points of alkenes decrease with increasing molecular weight, but show some variations that depend on the shape of the molecule. Alkenes with the same molecular formula are isomers of one another if the position and the stereochemistry of the double bond differ. For example, there are four different acyclic structures that can be drawn for butene (C4H8). They have different b.p. and m.p. as follows. 

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