Reaction due to α-hydrogen

Every student of Chemistry would have used the term Hydrogen on countless occasions. Here, we will be discussing about the various reactions due to alpha-hydrogen in the coming lines.

Reaction due to α-hydrogen

Due to the acidic nature of α-hydrogen of aldehydes and ketones, they undergo a number of reactions. This acidity is because of the strong electron withdrawing nature of the carbonyl groups and resonance stabilization of the conjugate base.

  • Aldol condensation: β-hydroxy aldehydes and β-hydroxy ketones are produced when aldehydes and ketones having one α-hydrogen undergoes a reaction in the presence of dilute alkali as a catalyst. This name Aldol is derived from the name of two functional groups aldehydes and alcohols. Water is lost by both Aldol as well as ketol to give α, β-unsaturated carbonyl compounds which are the products of aldol condensation and this reaction is called aldol condensation.
  • Cross aldol condensation: When two different aldehydes and ketones are involved in aldol condensation then it is called cross aldol condensation. We get the mixture of four products if both of them contains an α-hydrogen.
  • Cannizzaro reaction: When heated with an alkali, aldehydes and ketones which do have an α-hydrogen atom, undergoes self-oxidation and reduction reaction. One molecule in this reaction is reduced to aldehydes and one molecule is reduced to alcohol.
  • Electrophilic substitution reaction: In ring aromatic ketones and aldehydes, they undergo an electrophilic substitution reaction in which the carbonyl group acts as a deactivating group.

Uses of aldehydes and ketones:

  • For the synthesis of different products, aldehydes and ketones are used as solvents, reagents and starting materials.
  • For the preservation of biological specimens, preparation of bakelite and many more, we use formaldehyde which is also known as formalin.
  • For the manufacture of acetic acid, ethyl acetate and acetaldehydes.
  • Benzaldehyde is used in making perfumes and in dry industries.
  • Some of the common industrial solvents are acetone and ethyl methyl ketones.
  • Acetophenones, camphor and vanilla are some of the aldehydes and ketones that are used for flavour and colour.

From the above discussion, one could easily state that hydrogen has many applications for different industries and this is one of the main reasons why chemists around the world are conducting research on how to use α-hydrogen better in the coming years.


Practise This Question

Suppose you are a very competent surgeon in a super-famous hospital, which is located in Chennai. The year is 2004, 16 years after you joined as the chief of Surgery. The whole city is struck by a major tsunami and the non-stop rains have flooded your hospital. There is no electricity and you are in surgery with only 30 minutes of power backup, barely enough to sustain vital medical equipment and the lights. Your knowledge and experience suggest that you will be able to finish the surgery in not more than 18 minutes but the blood plasma has just precipitated. You cannot connect any more equipment but you will need to convert the precipitated blood into a colloid again or else the patient is no more. What do you do?