Everything Science Grade 12

CHAPTER 1. ORGANICMOLECULES 1.7

Formula Name Melting point (◦C) Boiling point (◦C) Phase at room temperature

CH 4 methane − 183 − 162 gas

C 2 H 6 ethane − 182 − 88 gas

C 3 H 8 propane − 187 − 45 gas

C 4 H 10 butane − 138 − 0. 5 gas

C 5 H 12 pentane − 130 36 liquid

C 6 H 14 hexane − 95 69 liquid

C 17 H 36 heptadecane 22 302 solid

Table 1.3: Properties ofsome of the alkanes

Reactions of the alkanes ESCN

There are three types ofreactions that can occurin saturated compoundssuch as the
alkanes.

1. Substitution reactions
   Substitution reactions involve the removal of a hydrogen atom which is replaced
   by an atom of anotherelement, such as a halogen (F, Cl, Br or I) (figure 1.11).
   The product is called a halo-alkane. Since alkanes are notvery reactive, either
   heat or light is needed for this reaction to take place.

e.g. CH 2 =CH 2 + HBr→ CH 3 -CH 2 -Br (halo-alkane)

H C

H

H

H

H

H

C H

C l

C l

2

light

+

Figure 1.11: A substitution reaction

Halo-alkanes (also sometimes called alkyl halides) that contain methaneand

chlorine are substancesthat can be used as anaesthetics during operations. One

example is trichloromethane, also known as ’chloroform’ (figure 1.12).

2. Elimination reactions
   Saturated compounds can also undergo elimination reactions to becomeunsatu-
   rated (figure 1.13). In the example below, an atom of hydrogen and chlorine are
   eliminated from the original compound to form an unsaturated halo-alkene.

e.g. ClH 2 C− CH 2 Cl→ H 2 C = CHCl + HCl