Chapter 10: Organic reactions: pathways to new products

10.1 Reactions of Alkanes

Alkanes contain strong carbon-carbon single bonds and strong carbon-hydrogen bonds. There are no partial charges on alkane molecules that might initiate reactions. The effect is that alkanes only undergo very few reactions.

(1) Combustion of alkanes

Alkanes can undergo combustion, producing CO2(g) and H2O(g)

When asked to create a combustion equation for a particular fuel, do the following steps:

  1. Write the fuel’s molecular formula
  2. Add excess O2(g)
  3. Produce CO2(g) and H2O(g)
  4. Balance C, H and O in that order.
  5. REMEMBER TO INCLUDE ALL THE STATES!

General formula: alkane + O2(g) → CO2(g) + H2O(g)

Example: C6H14(l) + O2(g) → 6CO2(g) + 7H2O(g) (halves are okay!)

(2) Substitution of alkanes

Alkanes can also undergo substitution, in which one of the hydrogen atoms is replaced with a halogen (e.g. F, Cl, Br, or I).

General formula: alkane + X2 → chloroalkane

Example: CH3CH3(g) + Cl2(g) + UV light → CH3CH2Cl(g) + HCl(g) (note that HCl is a gas!)

10.2 Reactions of alkenes

(1) Addition of alkenes

Alkenes can under addition reactions with halogens, hydrogen gas or water.

addition reactions of alkenes
Source: VCEasy.org

The first reaction happens at room temperature. If you have a gaseous alkene like ethene, you can bubble it through either pure liquid bromine or a solution of bromine in an organic solvent like tetrachloromethane. The reddish-brown bromine is decolourised as it reacts with the alkene.

(2) Addition polymerisation of alkenes
Source: Chemhume.co.uk

Chemguide links

Chemguide is an excellent revision resource that goes a little further than VCE. Read the relevant Chemguide pages below.

http://www.chemguide.co.uk/organicprops/alkanemenu.html
http://www.chemguide.co.uk/organicprops/alkenemenu.html
http://www.chemguide.co.uk/organicprops/estermenu.html

10.3 Oxidising ethanol to ethanoic acid

You will need to memorise the following ways to oxidise an alkanol into a carboxylic acid.

3 ways to oxidise alcohols
Source: VCEasy.org

For more information, visit this Chemguide page.

10.4: Making Esters

Table of Esters and their Smells
Click to enlarge

10.5: Organic Reaction Pathways

making esters from alkenes
Source: VCEasy.org

10.6: Fractional distillation

Fractional distillation can be used to separate compounds with different boiling points. It is commonly used in the separation of the compounds contained within crude oil.

More information about fractional distillation can be found here.

When hydrochloric acid is added to propene, two products can be produced: 1-chloropropane and 2-chloropropaneOnly the 1-chloropropane can be made into a carboxylic acid. We must therefore separate the 1-chloropropane from the 2-chloropropane by fractional distillation.

When reacting alkenes with 3 or more carbons (such as propene) with hydrochloric acid, we must write “HCl and fractional distillation” on the arrow.

For example:

propane fractional distillation
Source: Heinemann Chemistry 2

Click here for a 4-minute explanatory video about fractional distillation (beyond the VCE Chemistry course).

Read: Heinemann Chemistry 2 Chapter 10

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