1. Halogenoalkanes By Andrew Kropp, Hannah Couture, Mohamed Bounaim, and Amy Smith

2. What is a Halogenoalkane? a chemical compounds derived from an alkane containing one or more halogens Examples: Chlorofluorocarbons (ex. CH2ClF) Methyl bromide CH3Br Ethyl chloride C2H5Cl

3. How to name Halogenoalkanes Functional group = halogen Ex. Fluorine = fluoro Number by which carbon attached to, put in alphabetical order Ex. Bromoethane

4. More examples of Naming 1,1 dibromoethane 2 fluoropropane 1-bromo 2-methylpropane

5. Classification Halogenoalkanes can be classified as primary, secondary or tertiary depending on their structure Primary (1°) – carbon carrying halogen is attached to only one carbon alkyl group Secondary (2°)– carbon carrying halogen is attached to two other alkyl groups Tertiary (3°) – carbon carrying halogen is attached to three alkyl groups

6. Examples of Primary (1°)Halogenoalkanes ** Can you name these halogenoalkanes? (10 bonus points)

7. Examples of Secondary(2°)Halogenoalkanes

8. Examples of Tertiary (3°) Halogenoalkanes

9. Nucleophilic Substitution Reactions Halogenoalkanes react with substances such as sodium hydroxide to produce an alcohol through a reaction called nucleophilic substitution A nucleophile is a species (an ion or a molecule) which is strongly attracted to a region of positive charge in something else. Nucleophiles are either fully negative ions, or else have a strongly negative charge somewhere on a molecule. Common nucleophiles are hydroxide ions, cyanide ions, water and ammonia.

10. Nucleophilic Substitution Reactions Cont. Example using sodium hydroxide: The hydroxide ion acts as a nucleophile and is thus attracted to where the halogen has left the alkane and takes the place of the halogen These reactions are called Sn reactions (substitution nucleophilic) and there are two mechanisms for them: Sn 1 and Sn 2 The type of mechanism depends on whether the halogenoalkane is a primary, secondary, or tertiary alkane

11. Sn2 Mechanism – For primary halogenoalkanes Substitution nucleophilic bimolecular (called bimolecular because there are 2 reactants at the slow step) 1. slow step: OH¯ attacks Carbon 2. transition step: OH¯ and Cl¯ are partially bonded to C 3. fast step: alkane releases chloride ion, alcohol is formed

13. Sn1 Mechanism – For tertiary halogenoalkanes Substitution NucleophilicUnimolecular (because one reactant at slow step) *since there are 3 alkyl groups around carbon it creates a steric hindrance = the 3 bulky groups make it hard for OH¯ to attack the C 1. Halogenoalkane ionizes – the C-Halogen bond is broken, Halide ion takes electrons – there is a + charge on the carbon = carbocation 2. Alkyl groups donate electrons to keep it stable, OH¯ fills the open spot and it becomes an alcohol

14. Step 1: Step 2:

15. Mechanism of Secondary Halogenoalkanes They can use either Sn1 or Sn2 mechanism depending on the reaction conditions Many times they use a mixture of the two mechanisms, with the Sn1 being the majority

16. Reactivity of Halogenoalkanes The relative reactivity of halogenoalkanes depends on the Carbon-halogen bond strength and decreases down the group Examples: Iodoalkanes= weakest bond, most reactive Fluoroalkanes= strongest bond, least reactive

17. The End