Normal Alkanes Paraffins

The spectra of normal alkanes (paraffins) can be interpreted in terms of four vibrations, namely, the stretching and bending of C—H and C—C bonds. Detailed analysis of the spectra of the lower members of the alkane series has made detailed assignments of the spectral positions of specific vibrational modes possible. 

Not all of the possible absorption frequencies of the paraffin molecule are of equal value in the assignment of structure. The C—C bending vibrations occur at very low frequencies (below 500 cm-1) and therefore do not appear in our spectra. The bands assigned to C—C stretching vibrations are weak and appear in the broad region of 1200-800 cm they are generally of little value for identification. 

The vibrational modes of alkanes are common to many organic molecules. Although the positions of C—H stretching and bending frequencies of methyl and methylene groups remain nearly constant in hydro- 

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That the surface tensions of solutions of d- and /-optical isomers aredififerent seems doubtful. Surface tensions of normal alkanes (paraffin hydrocarbons) containing n atoms of carbon are given by a —l4-6 log ( —3)+ll 52 within experimental error. 

A paraffin wax is a petroleum wax consisting principally of normal alkanes. MicrocrystalHne wax is a petroleum wax containing substantial proportions of branched and cycHc saturated hydrocarbons, in addition to normal alkanes. SernimicrocrystaUine wax contains more branched and cycHc compounds than paraffin wax, but less than microcrystalHne. A classification system based on the refractive index of the wax and its congealing point as... 

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. 

Paraffins (Alkanes). These saturated aliphatic hydrocarbons include normal alkanes as well as branched alkanes (isoalkanes), represented by the formula The... 

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. 

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... 

Another important and well studied paramagnetic ion in the lattice of oxide semiconductors is Zr3+ in Zr02. Zirconia dioxide is widely used both as a catalyst of different chemical processes, and as a carrier for constructing supported metal-complex catalysts. In the last years, sulfated zirconia attracted significant interest as an active and selective catalyst in skeletal isomerization of normal alkanes at low temperatures, cracking of paraffins, alkylation and acylation of aromatics [42, 53 and Refs therein]. The appropriate experimental data are collected in the following Table 8.2. 

The pore openings of zeolite A just allow normal alkanes to enter the pore system of the crystal. It might be of interest to have a zeolite available which adsorbs the normals and the mono methyl-branched paraffins and leaves the high octane dimethyl branched compounds unadsorbed. 

Paraffin wax is macrocrystalline, bdtde, and is composed of 40-90 wt % normal alkanes, with the remainder isoalkanes and cycloalkanes. 

The waxy oil is fractionated to produce an oily wax called slack wax. This is separated by solvent extraction and fractionated into different melting point ranges to give waxes with a variety of physical characteristics. Paraffin waxes consist mainly of straight-chain alkanes (also called normal alkanes), with small amounts (3-15%) of branched-chain alkanes (or iso-alkanes), cycloalkanes, and aromatics. Microcrystalline waxes contain high levels of branched-chain alkanes (up to 50%) and cycloalkanes, particularly in the upper end of the molecular weight distribution. Paraffin waxes contain alkanes up to a molecular mass of approximately 600 amu, whereas microcrystalline waxes can contain alkanes up to a molecular mass of approximately 1100 amu. 

Normal alkanes (normal paraffins) ranging from C5 to C40 are often the most abundant constituents in many oils. Large n alkanes (>Cig) are often referred to as waxes. 

The separation of linear and branched alkanes is also of importance in the process known as dewaxing, in which the removal of normal alkanes makes the product hydrocarbon less viscous and reduces the so-called pour point temperature. Such processes can be combined with catalytic isomerisations to optimise the value of oil fractions (Chapter 8). Linear paraffins are also separated using a zeolite-based process from kerosene fractions to give reactants for the synthesis of linear alkylbenzene sulfonate anionic surfactants, which are both cost effective and biodegradable. 

Normal alkanes (straight-chain alkanes or normal paraffins) are the simplest homologous series of the group. 

The general appearance of the mass spectrum depends on the type of compound analyzed. We will look first at the normal alkanes (saturated straight-chain hydrocarbons of the formula C H2 +2. also called paraffins). Figure 10.13 shows the spectra of n-C,6 and n-C Q alkanes. It can be seen that... 

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