III. The suffix consists of the name of alkane as described for linear alkanes. The number of carbons (for determining the prefix of alkane's name) is determined by the formula: x + y + z + 2 where x and y are the number of carbon atoms in each of the rings and z is the number of carbons in the bridge. Thus, the name for compound 1 (x + y + z + 2 = 2+2+1+2 = 7) is bicyclo[2.2.1]heptane while that for compound 2 (x + y + z + 2 = 3+2+0+2 = 7) is bicyclo[3.2.0]heptane.

IV. If there is more than one bridge, as in case of polycyclic compounds, a main ring and a main bridge is to be selected. The main ring should contain as many carbon atoms as possible from the main skeleton. This count should begin from one of the bridge heads. If there is more than one bridge, then a main bridge is selected to include as many atoms as possible which are not contained in the main ring.

A prefix indicating the number of rings is to be prefixed. Thus, 3 and 4 both have 3 rings (tricyclo). Numbers for indicating lengths of carbon chains in each ring are to be placed in square brackets as in case of bicyclic compounds. In this case the secondary bridges are to be neglected while counting the atoms in the main ring. If however, there are secondary bridges, there should be additional superscript locants (the rule of lowest locants is valid) are to be written. The x + y + z +2 rule may be also applied here to find the parent name of the alkane.

3.3 Physical Properties

The lower members of alkanes are gases. As the molecular weight increases, they become liquids while still higher members are solids. Thus, the physical state changes from gas to liquid to solid as the molecular weight increases. Branching of alkanes also leads to lower boiling points. Thus, among the isomers of n-pentane, neopentane has the lowest boiling point. A similar effect is noticed in case of alkyl halides.

Alkanes are non-polar compounds and as such they are insoluble in water. In fact, solid alkanes behave as water repellents. Thus, the water proofing property of wax is an example of this property.

3.4 Preparation of Alkanes

The principal source of alkanes is naturally occurring petroleum and gas. Natural gas consists of mainly methane whereas petroleum consists of a complex mixture of various hydrocarbons which are then fractionally distilled to obtain either a mixture of hydrocarbons corresponding to boiling range or a pure hydrocarbon. Some of important constituents obtained by fractional distillation of petroleum are listed below (Table 2).

Table 2