1. Aldehydes and ketones: nucleophilic addition reactions

2. Aldehydes and ketones contain a carbonyl group, C=O.

3. Oxygen is a very electronegative element and the C=O bond is highly polar.

4. Nucleophiles can attack the partially positively charged carbon atom.

5. A covalent bond forms between the nucleophile and the carbon atom.

6. A pair of electrons from the carbon–oxygen double bond moves to the oxygen atom.

7. A carbon–oxygen single bond forms and the oxygen atom gains a negative charge.

8. A covalent bond forms between the oxygen atom and a hydrogen ion, H +. This ion can come from the solvent, water.

9. A hydroxyl group forms in the final product.

10. This is a general mechanism for nucleophilic addition in carbonyl compounds.

11. Let's look at the mechanism of the reaction between a carbonyl compound and the cyanide ion, CN –.

12. Oxygen is a very electronegative element and the C=O bond is highly polar.

13. The cyanide ion has a lone pair of electrons on its carbon atom. It acts as a nucleophile and it can attack the partially positively charged carbon atom.

14. A covalent bond forms between the cyanide ion and the carbon atom.

15. A pair of electrons from the carbon–oxygen double bond moves to the oxygen atom.

16. A carbon–oxygen single bond forms and the oxygen atom gains a negative charge.

17. A covalent bond forms between the oxygen atom and a hydrogen ion, H +. This ion can come from the solvent, water.

18. A hydroxyl group forms.

19. The final product is a hydroxynitrile.

20. Let’s look at the reaction mechanism when the carbonyl compound is an aldehyde, ethanal.

21. The final product is 2-hydroxypropanenitrile. It contains an asymmetric carbon atom and shows optical isomerism.

22. Let’s look at the reaction mechanism when the carbonyl compound is a ketone, propanone. The final product is 2-hydroxy-2-methylpropanenitrile, which does not show optical isomerism.

23. Let's look at the mechanism of the reaction between an aldehyde, ethanal, and a reducing agent such as sodium tetrahydridoborate(lll), NaBH 4.

24. Oxygen is a very electronegative element and the C=O bond is highly polar.

25. The BH – ion provides the hydride ion, H –. This has a lone pair of electrons and it acts as a nucleophile. It can attack the partially positively charged carbon atom.

26. A covalent bond forms between the hydride ion and the carbon atom.

27. A pair of electrons from the carbon–oxygen double bond moves to the oxygen atom.

28. A carbon–oxygen single bond forms and the oxygen atom gains a negative charge.

29. A covalent bond forms between the oxygen atom and a hydrogen ion from water, the solvent.

30. A hydroxyl group forms.

31. The final product is a primary alcohol, in this case ethanol.

32. This is the reaction mechanism when the carbonyl compound is a ketone, propanone. The final product is a secondary alcohol, in this case propan-2-ol.