Aliphatic hydrogens Hydrocarbons that

One of the characteristic features of the metal-catalysed reaction of acetylene with hydrogen is that, in addition to ethylene and ethane, hydrocarbons containing more than two carbon atoms are frequently observed in appreciable yields. The hydropolymerisation of acetylene over nickel—pumice catalysts was investigated in some detail by Sheridan [169] who found that, between 200 and 250°C, extensive polymerisation to yield predominantly C4 - and C6 -polymers occurred, although small amounts of all polymers up to Cn, where n > 31, were also observed. It was also shown that the polymeric products were aliphatic hydrocarbons, although subsequent studies with nickel—alumina [176] revealed that, whilst the main products were aliphatic hydrocarbons, small amounts of cyclohexene, cyclohexane and aromatic hydrocarbons were also formed. The extent of polymerisation appears to be greater with the first row metals, iron, cobalt, nickel and copper, where up to 60% of the acetylene may polymerise, than with the second and third row noble Group VIII metals. With alumina-supported noble metals, the polymerisation prod-... 

Mercury salts can react directly with hydrocarbons exchanging hydrogen for mercury. This reaction is an electrophilic substitution (equation 5) and hence can take place with arenes, cyclopentadienyls, terminal aUcynes, and also with aliphatic hydrocarbons that contain activated carbon-hydrogen bonds (e.g. carbonyl or nitrile compoimds). When the hydrocarbon contains several equivalent hydrogen atoms, polymercuration is often observed. 

Aliphatic hydrocarbon (unsaturated) a compound containing carbon and hydrogen only that has either an open-chain struc-... 

Any chemical compound of hydrogen and carbon also called an organic compound. Hydrogen and carbon atoms can be combined in virtually countless ways to make a diversity of products. Carbon atoms form the skeleton of the hydrocarbon molecule, and may be arranged in chains (aliphatic) or rings (cyclic). There are three principal types of hydrocarbons that occur naturally in petroleum parajfins, naphthenes, and aromatics, each with distinctive properties. Paraffins are aliphatic, the others cyclic. Paraffins and naphthenes are... 

Alkanes are saturated hydrocarbons that is, they contain only carbon-carbon single bonds. In this context, "saturated" means that each carbon has the maximum number of hydrogens bonded to it. We often refer to alkanes as aliphatic hydrocarbons, because the physical properties of the higher members of this class resemble those of the long carbon-chain molecules we find in animal fats and plant oils (Greek aleiphar, fat or oil). 

In Table 5.4, values for the interfacial tensions of various water/liquid interfaces, as calculated by the models of Fowkes and Girifalco and Good, are compared with measured values. It is clear that Fowkes model gives good results for aliphatic hydrocarbons that interact with water by dispersion forces only. As soon as polar interactions (tt electrons, dipoles, hydrogen bonding, etc.) play a role as well, strongly... 

The simplest organic compounds are the hydrocarbons, binary compounds of carbon and hydrogen. Hydrocarbons are divided into two major classes, the aliphatic hydrocarbons and the aromatic hydrocarbons. We will examine three groups of aliphatic hydrocarbons, the alkanes, the alkenes, and the alkynes. The features that distinguish aliphatic and aromatic hydrocarbons will be identified when we study the latter group. As you will see shortly, these classifications are all based on molecular structure. 

Alkenes are aliphatic hydrocarbons that have at least one double bond between carbons in the structure. The simplest alkene has two carbons. Its lUPAC name is ethene and its common name, also endorsed by the lUPAC, is ethylene (Figure 14.15). Notice that to accommodate the double bond, the carbons each have only two hydrogens. Remember that a carbon can have four bonds— no more and no less. This means that the carbons that are part of a double bond only have two remaining bonds each for use for other atoms such as hydrogen. 

As already mentioned molecules cohere because of the presence of one or more of four types of forces, namely dispersion, dipole, induction and hydrogen bonding forces. In the case of aliphatic hydrocarbons the dispersion forces predominate. Many polymers and solvents, however, are said to be polar because they contain dipoles and these can enhance the total intermolecular attraction. It is generally considered that for solubility in such cases both the solubility parameter and the degree of polarity should match. This latter quality is usually expressed in terms of partial polarity which expresses the fraction of total forces due to the dipole bonds. Some figures for partial polarities of solvents are given in Table 5.5 but there is a serious lack of quantitative data on polymer partial polarities. At the present time a comparison of polarities has to be made on a commonsense rather than a quantitative approach. 

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