Carboxyl Group: Overview, Questions, Preparation

Carboxyl group is an organic compound where the carbon (C) atom is connected by a single bond with the hydroxyl (OH) group and through a double bond to the oxygen (O) atom. The fourth bond connects the carbon atom to the hydrogen (H) atom. 

The primary chemical properties of the Carboxyl group is its acidity. They are more acidic than fellow organic compounds, which had hydroxyl in it but less acidic than known acid families. This is commonly found in nature in various forms, from citric acids in fruits to lactic acid in sour milk products to several types of kept acids in our body cells.

The IUPAC names have been taken from their similar alkanes and named just by replacing the ‘e’ of the hydrocarbon with ‘oic’ and adding ‘acid’ in the suffix. 

E.g., IUPAC Name- Ethanoic Acid 

      Chemical Structure- CH3COOH

When a compound has more than one carboxyl group, the groups are named accordingly to their numbers like di, tri, and so on before ‘oic’. 

Eg- IUPAC name - Pentanedioic acid

     Chemical Structure- HOOC -(CH2)3-COOH

Let us look at the physical properties of Carboxyl group.

1. Boiling Point- The Carboxyl group has higher boiling points than many other alcohols, hydrocarbons, ethers, ketones, and aldehydes. The minimum boiling point of one of the carboxyl groups is 101 oC.
2. Acidity- This is one of the most important properties of the Carboxyl group. They are stronger than their fellow organic compounds but weaker than familiar acids.
3. Odour- Some of the carboxylic acids, unbranched ones that are liquid at normal temperature, produce an unbearable foul odour. A common example is Butyric Acid which is the main component in sweat glands and is released from bodies and is commonly known as ‘locker-room’ odour.
4. Solubility- The solubility feature of this group is very similar to aldehydes, alcohols, and ketones. The carboxyl group with less than five carbon atoms would dissolve in water, but it is insoluble for the members with higher molecular weight. But the ammonium, sodium, and potassium salts of this carboxyl group are soluble in water.

The details on the Carboxyl group can be found in details in the Class XII book. Many features have been explained in it, along with examples for a better understanding of the topic. It talks about the chemical structures of different compounds, methods of preparations and reactions with different compounds, understanding the mechanism of reactions with ketones and aldehydes and many more.

I. Name the following compounds according to their IUPAC nomenclatures.

Solution: 

1. CH3CH=CHCHO- But-2-enal
2. CH3CH2COCH(C2H5)CH2CH2Cl- 6-Chloro-4-ethylhexan-3-one
3. OHCC6H4CHO-p- Benzene-1,4-dicarbaldehyde
4. CH3CH(CH3)CH2C(CH3)2COCH3- 3,3,5-Trimethylhexan-2-one

II. Draw the structures of the following compounds

Solution: 1. Cyclopropane oxime- 

2. The semicarbazone of cyclobutanone

III. Name the product formed when cyclohexanecarbaldehyde reacts with 

(a) Semicarbazide and weak acid 

(b) Tollens’ reagent

Solution: (a)- 2-Methylcyclopentanecarboxylic acid

               (b) 3-Methylbut-2-enoic acid

[Image courtesy: NCERT]

Q: What is the composition of a carboxyl group?

A: The carboxyl group consists of Carbon, Oxygen, and hydroxyl groups. The Carbon and oxygen atoms are connected by a single bond, whereas a double bond connects the carbon and the hydroxyl atoms.

Q: What is the angle between the compounds of the carboxylic group?

Q: How do you name a compound which has more than one carboxyl group?

Q: What is the minimum boiling point of the carboxylic group?

Q: What kind of odour does carboxylic acid produce?