Describe the differences between primary, secondary and tertiary halogenoalkanes.

Primary, secondary and tertiary halogenoalkanes differ in the number of carbon atoms bonded to the carbon atom with the halogen.

Primary halogenoalkanes have the halogen atom bonded to a carbon atom that is only bonded to one other carbon atom. Secondary halogenoalkanes have the halogen atom bonded to a carbon atom that is bonded to two other carbon atoms. Tertiary halogenoalkanes have the halogen atom bonded to a carbon atom that is bonded to three other carbon atoms.

The reactivity of halogenoalkanes increases as the number of carbon atoms bonded to the carbon atom with the halogen decreases. This is because the carbon-halogen bond becomes weaker as the carbon atom becomes more substituted, making it easier for the halogen to leave and for a nucleophile to attack.

Primary halogenoalkanes are the least reactive and require strong nucleophiles and high temperatures to undergo substitution reactions. Secondary halogenoalkanes are more reactive and can undergo substitution reactions with weaker nucleophiles and at lower temperatures. Tertiary halogenoalkanes are the most reactive and can undergo substitution reactions with very weak nucleophiles and at room temperature.

The boiling points of halogenoalkanes also increase as the number of carbon atoms bonded to the carbon atom with the halogen increases. This is because the larger molecules have more surface area for London dispersion forces to act upon, making them more difficult to separate.