Organic synthesis of aliphatic and aromatic compounds

What is organic synthesis:

Synthetic routes in aliphatic / aromatic chemistry:

Aliphatic routes:

Aliphatic routes:

The general approach:-


·        For a 2 step synthesis:-

1        Examine the starting molecule’s functional group.

2        Examine the target molecules functional group.

3        Note which functional group has been changed on the starting molecule.

4        Note what that functional group has been changed to in the target molecule.

5        Using your knowledge maps, find the intermediate functional group that the starting molecule can be changed to and the target molecule can be made from.

6        Apply the conditions and you have a 2 step synthesis.


Example 1:


Starting molecule:–       propene

Target molecule:–          propanoic acid


2 – step synthesis:-


                                       CH3CH = CH2      ŕ      Unknown      ŕ      CH3 – CH2– COOH



                                       CH3CH = CH2      ŕ      CH3 – CH2 – CH2OH      ŕ      CH3 – CH2– COOH


Step 1:-          Steam and phosphoric acid

Step 2:-          Reflux with sulphuric acid and potassium dichromate


Example 2:


Step 1:

Step 2:


Example 3:


Step 1:

Step 2:


Task:  Collate all your organic reactions diagrams from AS and A2 (include reagents and conditions)

Once you have completed the task aabove:

Have a go at synthesising:

  1. 1,2-Dibromobutane from butan-1-ol
  2. Butanoic acid from 1-bromobutane
  3. Ethane from ethanol
  4. Ethyl ethanoate from ethene
  5. Ethlamine from ethanol
  6. phenylamine from benzene
  7. 3 - chloronitrobenzene from benzene

Qu 1 P63   1,2  P65

Designing a two step synthesis:



Optical isomerism


Task:  Build a molecule using:


            Black molymod in the centre

            Attatch a green, blue, red and white molymod to the central black molymod:


Your teacher will guide you what to do from here.



Optical isomers:

When a carbon atom has 4 different groups attached to it, you get 2 shapes that are mirror images of each other, known as optical isomers.  The carbon atom is called the ‘Chiral Centre’.

Properties of optical isomers:

Optical activity and amino acids:

Qu 1 - 3  P53


Chirality in pharmaceutical synthesis


The importance of chirality in drug synthesis:




  • Seldane was the first antihistamine on the market to combat hay fever.

  • The drug is chiral.

  • One stereoisomer relieved hayfever.

  • The other caused potentially fatal heart conditions.


Synthesising pharmaceuticals:

Synthesis Vs Nature:


  Synthesis Nature
Isomers Both one
Made In the laboratory In the body
Dose Twice needed Half needed
Side effects Probably None
Cost Cheaper More expensive
Separation in lab Usual chemical difficult - isomers have same physical and chemical properties Using enzymes - costly and time consuming


Modern chiral synthesis:

1)  Using enzymes as biological catalysts:

2)  Chiral pool synthesis:

3)  Use of transition metal complexes:

Chiral drugs at home:

Qu 1 - 3   P67  /    Qu  3   P 69   /   Qu 1b,7,8  P72