The simplest hydrocarbons are alkanes. In these compounds, all the bonds of carbon atoms are single that means valencies of carbon atoms are saturated. Therefore, they are least reactive. That is the reason, alkanes are called paraffins (para means less, and affins means affinity or reactivity).
Alkanes form a homologous series of compounds in which each successive member of the series differs by a group but they have similar structures and similar chemical properties. The first member of the series is methane , next ethane , then next propane and so on as given in the previous chapter Table 11.3. The electron cross and dot structures of simple alkanes are presented as follows:
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Sources of Alkanes
12.1.1 Preparation of Alkanes
As we know, alkanes form a series of homologous compounds. So, their methods of preparation and chemical properties are similar. Although, there are many methods of preparation, but only two methods are discussed here.
12.1.1.1 Hydrogenation of Alkenes and Alkynes
Hydrogenation means addition of molecular hydrogen in alkenes and alkynes. As we know, alkenes and alkynes are unsaturated compounds, so they have the capacity to add up atoms in them. This reaction is carried out in the presence of nickel catalyst at to . However, in the presence of catalyst platinum or palladium, the reaction takes place at room temperature, such as:
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12.1.1.2 Reduction of Alkyl Halides
Reduction means addition of nascent hydrogen. In fact, it is a replacement of a halogen atom with a hydrogen atom. This reaction takes place in the presence of Zn metal and HCl.
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