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Name Reactions- Aldol Condensation, Cannizzaro, Claisen-Schmidt, Perkin, Benzoin, Sandmeyer, Gattermann, Wurtz, Friedel crafts reaction,Practice Problems & FAQs

Have you seen the contacts list on your phone? There is a long list of names with unique and different mobile numbers for each contact, which we use to connect with the said person. In a similar fashion, to classify, study, and analyze the long list of organic reactions, many of these reactions have been named after the scientists who discovered them.

TABLE OF CONTENT

  • Aldol Condensation Reaction
  • Cross-Aldol Condensation Reaction
  • Cannizzaro Reaction
  • Cross Cannizzaro Reaction
  • Claisen-Schmidt Reaction
  • Perkin Reaction
  • Claisen Condensation Reaction
  • Dieckmann Cyclisation
  • Benzoin Condensation Reaction
  • Sandmeyer Reaction
  • Gattermann Reaction
  • Wurtz Reaction
  • Wurtz-Fittig Reaction
  • Fittig Reaction
  • Friedel-Crafts Alkylation Reaction
  • Friedel-Crafts Acylation Reaction
  • Clemmensen Reduction Reaction
  • Practice Problems
  • Frequently asked questions
  • Related Topics

Aldol Condensation Reaction

Aldol condensation is a reaction where two small carbonyl molecules are condensed or joined to give rise to a bigger molecule. Aldol condensation reaction usually takes place between two aldehydes or ketones. Two similar carbonyls react and give rise to a product containing one carbonyl group and another alcoholic group. The product formed is called aldol product, followed by condensation ,-unsaturated carbonyl compounds are formed as a final product.


Condition for Aldol Condensation

Generally, For a molecule to give an aldol condensation reaction, it should contain alpha hydrogen.

Cross-Aldol Condensation Reaction

Cross-aldol condensation is a reaction where two different aldehydes or ketones react to form different products. Cross-aldol condensation usually takes place between

  1. Different aldehydes
  2. Different ketones
  3. One aldehyde and one ketone

Example: 

Find out the product.


4 products are formed in a cross aldol condensation reaction.

Product 1: Self Aldol Product


Product 2: Self Aldol Product


Product 3: Cross Aldol Product


Product 4: Cross Aldol Product


Cannizzaro Reaction

In the presence of a strong base like Sodium Hydroxide, two similar aldehydes react to form an acid and alcohol. For a Cannizzaro reaction to take place, the aldehydes must not have α hydrogens. The steps involved in the Cannizzaro reaction include:

Cannizzaro reaction is a redox reaction.


Cross Cannizzaro Reaction

The Cross Cannizzaro reaction is similar to the Cannizzaro reaction. The only difference is that the cross Cannizzaro reaction takes place between two different aldehydes. Cross Cannizzaro reaction also takes place in the presence of a strong base and involves the same steps as seen in the Cannizzaro reaction.


Claisen Schmidt Reaction

Claisen Schmidt reaction is a cross aldol reaction. It takes place when one reactant is a ketone and another one is an aldehyde with no -H.

The steps involved in the Claisen Schmidt reaction are:

1. Formation of enolate
2. Addition of Enolate
3. Dehydration/Condensation

Example:


Perkin Reaction

Perkin reaction is a reaction where an aromatic aldehyde reacts with an acid anhydride to give rise to an α, β - unsaturated product. Perkin reaction takes place in the presence of carboxylic salt of sodium and potassium. 

For a Perkin reaction to take place, the acid anhydride must contain at least one α hydrogen.

Example:


Claisen Condensation Reaction

Claisen condensation is a reaction where two similar esters react to form a molecule called -keto ester. The reaction occurs in the presence of a strong base (RO-) .


Dieckmann Cyclisation

Dieckmann cyclisation is a reaction where diesters react to form a molecule called -keto ester. The reaction occurs in the presence of a strong base (RO-), and this reaction is basically an intramolecular claisen condensation reaction.

Example:

Benzoin Condensation Reaction

Benzoin condensation is a reaction where two similar aromatic aldehydes react to form a molecule called Benzoin. The reaction occurs in the presence of a cyanide ion (KCN or NaCN) and a solvent like ethyl alcohol. The product formed i.e. benzoin consists of a ketone and alcoholic group. For the benzoin reaction to take place, the reactants must not contain α hydrogens. 

Example:

Sandmeyer Reaction

Sandmeyer’s reaction is a substitution reaction. In this reaction, aryl diazonium salts give rise to aryl halides(chlorides/ bromides) in the presence of Sodium nitrite - HX and CuX. The amine group present in the aryl diazonium salt is displaced with a halide ion. 

Example:

Gattermann Reaction

Gattermann reaction is a chemical reaction where benzene diazonium salt reacts with HX and Copper powder to give rise to a benzene molecule containing the halide ion(chloride/bromide). The HX used for the reaction should correspond with the halide ion present in the benzene diazonium salt.


Wurtz Reaction

Wurtz reaction is a chemical reaction where alkyl halides react with Na in the presence of dry ether. The number of carbon atoms present in the alkyl halide after the Wurtz reaction is twice that of carbon atoms present in the alkyl halide before the reaction, hence this is a coupling reaction.


Wurtz-Fittig Reaction

Wurtz - Fittig reaction is a chemical reaction taking place between an aryl halide and alkyl halide, thereby giving rise to an alkyl arene. Wurtz - Fittig reaction takes place in the presence of dry ether and Sodium.

Example:

Fittig Reaction

A Fittig reaction is a chemical where two aryl halides react in the presence of Sodium and dry ether. The product formed by the Fittig reaction consists of two aryl groups joined by a single bond.

Example:

Friedel-Crafts Alkylation Reaction

Friedel-crafts alkylation is a reaction where benzene reacts with an alkyl halide to give rise to alkylbenzene. This reaction usually takes place in the presence of anhydrous aluminum chloride. In this reaction, the alkyl group present in alkyl halide replaces one hydrogen atom of benzene, thereby alkylating the benzene molecule.

Example:

Friedel-Crafts Acylation Reaction

Friedel-crafts acylation is a reaction where benzene reacts with an acyl halide to give rise to acyl benzene. This reaction usually takes place in the presence of Lewis acids such as anhydrous aluminium chloride. In this reaction, the acyl group present in acyl halide replaces one hydrogen atom of benzene, thereby acylating the benzene molecule.

Example:

Clemmensen Reduction Reaction

Clemmensen reduction is a chemical reaction where ketones and aldehydes react with the zinc-amalgam mixture in the presence of HCl. The carbonyl group is reduced to the CH2 group.

Example:

Practice Problems

Q 1. In the presence of cold dilute alkali, which of the following compounds shows self-aldol condensation reaction?

a. C6H5CHO
b. CH3CH2CHO
c. HCCCHO
d. CH2=CHCHO

Answer: An aldol condensation is a condensation reaction in which an enol or an enolate ion reacts with a carbonyl compound to form a β-hydroxyaldehyde or β-hydroxyketone, followed by dehydration to an α,β-unsaturated aldehyde or α,β-unsaturated ketone.

Aldol condensation occurs in aldehydes having α-hydrogen.

Only B has saturated α-hydrogen thus it will undergo aldol condensation.

So the correct option is B.

Q 2. When two different carbonyl compounds containing α-hydrogens react in the presence of dilute NaOH and heat, the reaction is known as.

a.  Aldol condensation
b. Self-condensation
c. Cross aldol condensation
d. None of the above

Answer: Aldol condensation occurs in aldehydes having α-hydrogen with a dilute base to give β-hydroxy aldehydes called aldols. This reaction is known as aldol condensation. If the aldol condensation reaction occurs between two different carbonyl compounds it is called cross aldol condensation.

So, the correct option is C.

Q 3. Cannizzaro reaction is given by which of the following molecules?

a. HCHO
b. CH3COCH3
c. CH3CHO
d. CH3CH2OH
Answer: Aldehydes with no α−H atom undergo Cannizzaro reaction on heating with concentrated alkali solution.
Only HCHO does not have an α−H atom thus it will undergo the Cannizzaro reaction.
So, the correct option is A.

Q 4. The species that are most likely to be the intermediate during benzoin condensation of benzaldehyde are? 

1

Answer: 
When benzaldehyde is heated with aqueous ethanolic NaCN or KCN, it dimerizes to form an α−hydroxy ketone called benzoin and thus this reaction is known as benzoin condensation.

Mechanism of Benzoin condensation reaction:

1. Nucleophilic addition of cyanide:



2. Nucleophilic addition of carbanion:



3. Removal of cyanide:



So, the correct option is C. 

Frequently Asked Questions - FAQ

Q 1. Why is Sandmeyer's reaction better than Gattermann's reaction?
Answer:
Sandmeyer reaction is preferred over Gatterman due to better yield in the case of Sandmeyer reaction.

Q 2. Will all aldehydes with alpha hydrogen show an aldol condensation reaction?
Answer:
Aldehydes with alpha hydrogen generally show an aldol condensation reaction but the aldehyde in which alpha hydrogen is sterically hindered will not give an aldol condensation reaction.

Q 3. If two aldehydes one with Hydrogen and one without hydrogen, which reaction will take place aldol or Cannizzaro? 
Answer:
When two aldehyde reacts with each other and at least one is having -H aldol condensation reaction takes place.

Q 4. Why does cyclopropanone not show an aldol condensation reaction?
Answer:
Due to the high ring strain in cyclopropanone, the nucleophilic attack will open the three-membered ring instead of nucleophilic addition.

Related Topics

Friedel-Craft’s reaction

Chorination

Toluene

Wurtz reaction

Structure and Reaction of Benzene

Electrophilic Aromatic Substitution reactions of benzene






 

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