Figure 4-15. The two alkanes used in octane number determination.
The branch of chemistry that deals with studies of crude oil is called petrochemistry
. Industrial plants for converting crude oil to useful products, called oil refineries
, employ numerous chemical transformations as well as separation techniques and purification processes. It is worth to note that, in principle, alkane fuels can be produced without oil. During World War II, Germany, a country without natural oil reserves, was blockaded from external oil supplies and had to use synthetic oil
, which was produced from coal by various chemical methods.
Although methods exist for small-scale preparation of alkanes, these methods are rarely used in chemical laboratories for two main reasons. First, many pure alkanes are commercially available from petrochemical and fine chemical industries. Second, laboratory methods to prepare alkanes are rather limited. If you are interested, you may familiarize yourself with two older methods, the Wurtz reaction
and the Kolbe electrolysis
, developed by Charles Adolphe Wurtz (1817-1884) and Hermann Kolbe (1818-1884), respectively. In organic chemistry, particularly important chemical transformations are often named after their discoverers. Such transformations are called Organic Name Reactions
. We will encounter more of such reactions in due course. 4.2.7. Chemical Properties of Alkanes.
An alternative name for alkanes is paraffins
. The word paraffin
is derived from two Latin words parum
, together meaning "insufficient affinity" (insufficient reactivity). Indeed, alkanes are very poorly reactive compounds. Three factors contribute to the high chemical inertness of alkanes. First
, Lewis structures of alkanes show that all C atoms in their molecules have 8 electrons in the outer shell (Figure 4-16). In accord with the octet rule, the carbon atoms of alkanes are "happy". So are the hydrogen atoms, which all have two electrons in their outermost shells. There are neither lone electron pairs on alkane molecules, which would make them reactive toward electron acceptors, nor low-lying vacant orbitals for reactions with electron donors.