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Aldehydes, Ketones and Carboxylic Acid, are the organic compounds containing Carbonyl group (CO) as the functional group. The carbonyl compounds are one of the most important functional groups that are widely used in organic chemistry.
- Aldehydes, Ketones and Carboxylic Acid consist of a carbon-oxygen double bond.
- The term carbonyl in the carbonyl group is referred to as carbon monoxide.
- The Carbonyl group will form an aldehydes when carbon and hydrogen atoms are bonded.
- In the case of ketones, hydrogen is bonded to two carbon atoms.
- Carboxylic Acid is formed when the carbonyl group are bonded to an oxygen atom.
- Aldehydes and Ketones combined with other functional groups are excessively used for many industrial purposes.
- Carboxylic acids are used in the Cannizzaro Reaction.
- Aldehydes, Ketones and Carboxylic Acid, are divalent to the C atom.
Key Terms: Aldehydes, Ketones, Carboxylic Acid, Aldehydes, Ketones and Carboxylic Acid, Carbonyl Group, Carbon Oxygen Bond, Hydrogen, Atom, Halogen, Nitrogen, Amides, Functional Group
What are Aldehydes?
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Aldehydes are an organic compound consisting of an alkyl group on one end and a hydrogen atom on the other. These are volatile and flammable liquids which will convert into vapour at room temperature.
- The acyclic and aliphatic aldehydes are primarily named after their longest carbon chain.
- They also have "al" attached to the suffix.
- When the aldehyde functional group is contained in a ring compound, the "carbaldehyde" suffix is used.
- For natural carboxylic acids, the "oxo" prefix is used to highlight the carbon which is included in the aldehyde functional group.
Structure of Aldehyde
Aldehydes is a compound in organic chemistry that consists of a functional group with the structure R−CH=O. The R denotes the alkyl or aryl group. The structure of aldehyde is represented as:
Preparation of Aldehydes
Various ways to prepare aldehydes are as follows:
Rosenmund Reduction Reaction
Aldehydes are produced by the reduction of acid chlorides. Hydrogen in presence of palladium catalyst sprayed on barium sulfate acts as a catalyst to the reaction. This reaction is known as the Rosenmund reduction reaction.
- It is mainly used for the preparation of various aromatic aldehydes.
- The process cannotbe used for preparing formaldehyde for ketones.
Stephen Reaction
The aldehyde can be prepared from nitriles and esters. This reaction is called the Stephen reaction.
Etard Reaction
Apart from that, aldehydes can also be prepared from hydrocarbons through the Etard reaction. The Gaterman-Koch reaction is also popular for the preparation of benzaldehyde.
Properties of Aldehydes
The important properties of aldehydes are as follows:
- The hybridization of the aldehyde group is sp2.
- They are highly soluble in water.
- Aldehydes have higher boiling points in comparison to hydrocarbons.
- They undergo oligomerization or polymerization reactions.
- Aldehydes are volatile in nature and have a pungent odour.
- They can be detected by spectroscopic methods.
Uses of Aldehydes
The various uses of aldehydes are as follows:
- Formaldehyde can be used as a potential disinfectant.
- Aldehydes are used for mirror silvering.
- The compound is used to manufacture acetic acid.
- Aliphatic aldehydes are used in the creation of perfumes.
- Benzaldehyde is used to manufacture of rubber accelerators.
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What are Ketones?
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Ketone is a class of organic compounds in which the carbon atom forms a covalent bond with an oxygen atom. It consists of two hydrocarbon compounds that are either benzene rings or alkyl groups.
- In the case of ketones, the parent alkane’s name is taken into account.
- The “anone” suffix is attached to it.
- The carbonyl group’s position is denoted by a particular number, while a particular name is given to the ketone.
- The names of the alkyl groups that are attached to the carbonyl compound are also included in the nomenclature.
Structure of Ketone
Ketone is an organic compound that consists of a functional group with the structure R-(C=O)-R’. The R and R’ are various types of carbon substituents. It consists of trigonal planar which is centred around the carbonyl carbon.
Preparation of Ketone
Various ways to prepare ketone are as follows:
Grignard Reaction
Ketones are prepared when acid chloride reacts with dialkyl cadmium. Dialkyl cadmium is prepared from Grignard reagent. This method is one of the most popular ways of preparing ketones.
Friedel-Crafts Acylation Reaction.
Ketones can be prepared using nitriles compound. Benzene or substituted benzene can also be used for ketone preparation. This method is called Friedel-Crafts acylation reaction.
Physical Properties of Ketone
The important properties of Ketone are as follows:
- The bond angle of the ketone is calculated to be around 120 degrees.
- Ketones generally have higher boiling points than hydrocarbons, and ethers have similar masses.
- Other ketones are either solid or liquid at room temperature
- The solubility of these compounds increases as the length of the alkyl chain increases.
- Ketone has large dipole moments.
- When the compound is added to sodium bisulphite, then it will form bisulphite.
Chemical Properties of Ketone
The important chemical properties of Ketone are as follows:
- Ketones undergo nucleophilic reactions.
- A nucleophile will attack the electrophilic carbon of the carbonyl group to form different compounds.
- These compounds undergo additional reactions with ammonia and its various derivatives.
- Ketones also react with the Grignard reagent.
- Apart from that, aldehydes and ketones also undergo various oxidation and reduction reactions.
Uses of Ketone
The various uses of Ketone are as follows:
- Ketones like propanone can be used for the preparation of polymers.
- Acetone is used as an industrial solvent.
- It is used for the treatment of acne.
- Ketone is used in paraffin wax, varnishes, plastics and paint remover.
What are Carboxylic Acids?
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Carboxylic acids contain carboxyl functional groups. They basically contain a carbonyl group, which is attached to a hydroxyl group. The carboxylic acid can either be aliphatic or aromatic, depending on the structure of the parent carbon chain.
- Carboxylic acids are named by the addition of an “oic acid” suffix to the parent carbon chain.
- Even if other substituents are present, it will be considered at the first position of the parent carbon chain.
- The carboxylic group can also be used as a substituent in the parent carbon chain.
Structure of Carboxylic Acids
The carboxyl carbon bonds of the carboxylic acid lie on one plane. The bonds are separated by 120 degrees. The carboxylic carbon has less electrophilic property than the carbonyl compound. This occurs because of the resonating structures.
Carboxylic acid
Preparation of Carboxylic Acids
Various ways to prepare carboxylic acids are as follows:
Alcohol
Carboxylic acids are mainly prepared from primary alcohols and acids by the presence of a very strong oxidizing agent.
Alkyl Benzene
They can also be prepared from alkyl benzene by using an oxidizing agent.
Grignard Reaction
Carboxylic acids can also be prepared using nitriles and amides. Sometimes, the Grignard reagent is also used.
Physical Properties of Carboxylic Acid
The physical properties of carboxylic acid are as follows:
- Aliphatic carboxylic acids which have up to nine carbon atoms are mainly liquid at room temperature.
- They mostly have an unpleasant odor.
- Higher carboxylic acids are waxy solids.
- They are mostly odorless.
- Carboxylic acids mostly have higher boiling points as compared to alcohols, ketones, and aldehydes of similar masses.
- Solubility decreases with an increase in the number of carbon atoms.
Chemical Properties of Carboxylic Acid
The chemical properties of carboxylic acid are as follows:
- Carboxylic acids react with metals and salts to liberate hydrogen gas.
- This contributes to their acidic properties.
- They also react with carbonates and bicarbonates to liberate carbon dioxide gas.
- These compound when heated with mineral acids from their corresponding anhydrides.
- They undergo esterification reactions when they are reacted with alcohols or phenol in the presence of a catalyst.
- Carboxylic acids also react with ammonia to form ammonium salts.
- Apart from that, they also undergo reduction, halogenation, and decarboxylation reactions.
Uses of Carboxylic Acids
Some of the uses of carboxylic acids are as follows:
- Methanoic acid in the textile, rubber, leather and dyeing industry.
- Ethanoic acid is an important part of the food industry.
- It is used in the preparation of vinegar.
- Ethanoic acid is also used as a solvent.
- Hexanedioic acid for manufacturing nylon.
- Different esters of benzoic acid can be used for the preparation of different perfumes.
- Carboxylic acids can be used as food preservatives.
What are Carbonyl Groups?
Carbonyl compounds are those compounds that contain a carbon-oxygen double bond in them. These compounds are an extremely important part of organic chemistry.
- Carbonyl compounds consist of the carbon-oxygen double bond.
- Aldehydes, Ketones and Carboxylic Acid belong to the class of carbonyl group.
- However, it has free hydrogen atoms, which makes them more reactive.
- Aldehydes consist of the bonding of the carbonyl group to carbon and hydrogen.
- In the case of ketones, the carbonyl group bonds with two carbon atoms.
- When the carbon is connected to nitrogen and halogens, they are known as amides and acyl halides, respectively.
Structure of Carbonyl Groups
The structure of carbonyl group are as follows:
- The carbon atom is a sp²-hybridized atom.
- It forms three sigma bonds.
- The fourth valence electron remains in the p-orbital.
- It forms a Pi bond with the oxygen by overlapping with the p-orbital of the oxygen atom.
- The carbonyl carbon, along with its three atoms, lie in the same plane, while the π-electron cloud lies above and below the plane.
- The bond angle is around 120 degrees.
Things to Remember
- Aldehydes, Ketones and Carboxylic Acid belong to the class of carbonyl groups compounds.
- The boiling points of carboxylic acid are higher than that of aldehydes and ketones.
- When it comes to reactivity, aldehydes are more reactive as compared to ketones.
- In carboxylic acids, “-oxo” is used as a prefix whereas in aldehyde “al” is attached to the suffix.
- Ketone has “anone” suffix attached to it.
Read More:
| Class 12 Chemistry Related Concepts | ||
|---|---|---|
| Gattermann – Koch Reaction | Williamson Ether Synthesis | Electrophilic Aromatic Substitution |
| Ester Hydrolysis | Reimer Tiemann Reaction | Gabriel phthalimide synthesis |
Sample Questions
Ques: Name the reagents used in the following reactions : (2 Marks)
Ans: The reagents used are as follows:
(i) LiAlH4 (Lithium Aluminium Hydride)
(ii) KMnO4 (Alkaline Potassium Permanganate)
Ques: Arrange the following compounds in increasing order of their property as indicated :
(i) CH3COCH3, C6H5COCH3, CH3CHO
(reactivity towards nucleophilic addition reaction)
(ii) Cl—CH2—COOH, F—CH2—COOH, CH3—COOH (acidic character) (2 Marks)
Ans: The order is as follows:
(i) C6H5COCH3 < CH3COCH3 < CH3CHO
(Reactivity towards nucleophilic addition)
Ques: Write the equations involved in the following reactions:
(A) Wolff-Kishner reduction
(B) Etard reaction (2 Marks)
Ans: The equations involved are as follows:
(A) Wolff-Kishner reduction
(B) Etard reaction
Ques: Write the reactions involved in the following:
(i) Hell-Volhard Zelinsky reaction
(ii) Decarboxylation reaction (2 Marks)
Ans: The equations involved are as follows:
Ques: Predict the products of the following reactions : (3 Marks)
Ans: The equations involved are as follows:
Ques: Predict the products of the following reactions : (3 Marks)
Answer: The equations involved are as follows:
Ques: Write structures of compounds A, B and C in each of the following reactions: (3 Marks)
Ans: The equations involved are as follows:
A = Ethanal
B = 3-Hydroxybutanal (Aldol)
C = But-2-enal
Ques: Write the reagents required in the following reactions : (3 Marks)
Ans: The equations involved are as follows:
Ques: (a) Give chemical tests to distinguish between the following pairs of compounds :
(i) Ethanal and Propanal (ii) Phenol and Benzoic acid
(b) How will you bring about the following conversions?
(i) Benzoic acid to benzaldehyde (ii) Ethanal to but-2-enal (iii) Propanone to propene
Give a complete reaction in each case. (5 Marks)
Ans: The process involved are as follows:
(a) (i) Ethanal and Propanal : To distinguish between ethanal and propanal we can perform an iodoform test. First you need to warm both the compounds with iodine and sodium hydroxide solution in water. Ethanal gives yellow crystals of iodoform while propanal does not respond to the iodoform test.
(ii) Phenol and Benzoic acid: After adding NaHCO3 to both solutions we can observe carbon dioxide gas is evolved with benzoic acid while phenol does not form CO2.
Ques: (a) Give chemical tests to distinguish between
(i) Propanal and Propanone, (ii) Benzaldehyde and Acetophenone.
(b) How would you obtain
(i) But-2-enal from Ethanal, (ii) Butanoic acid from Butanol,
(iii) Benzoic acid from Ethylbenzene. (5 Marks)
Ans: The process involved are as follows:
(a) (i) Propanal and propanone: Propanal gives a positive test with the Fehling solution in which a red ppt. of cuprous oxide is obtained while propanone does not respond to test
(ii) Benzaldehyde and acetophenone :
By Iodoform test : Acetophenone being a methyl ketone on treatment with I2/NaOH (NaOI) undergoes iodoform test to give yellow ppt. of iodoform but benzaldehyde does not.
(b) (i)
(ii)
(iii)
Ques: What will happen when ketone react with chloride. (2 marks)
Ans: Ketones are prepared when acid chloride reacts with dialkyl cadmium. Dialkyl cadmium is prepared from Grignard reagent. This method is one of the most popular ways of preparing ketones.
Ques: What are various techniques used for preparation of carbonyl groups. (3 marks)
Ans: Various techniques used for preparation of carbonyl groups are as follows:
- Carboxylic acids are mainly prepared from primary alcohols and acids by the presence of a very strong oxidizing agent.
- They can also be prepared from alkyl benzene by using an oxidizing agent.
- You can also prepare carboxylic acids using nitriles and amides. Sometimes, the Grignard reagent is also used.
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