Carboxylic acid is a compound that has a carbonyl group bonded to an ¬OH group, RCOOH.

Ester is a compound that has a carbonyl group bonded to an ¬OR′ group, RCOOR′.

Amide is a compound that has a carbonyl group bonded to a nitrogen-atom group, RCONR′ 2, where the R′ groups may be alkyl groups or hydrogen atoms.

Since carboxylic acids, esters, and amides all contain a carbonyl carbon atom (C=O) bonded either to an oxygen or to a nitrogen, they are all polar.

• Their structural similarities also account for many similarities in the properties of these compounds. Thus they all boil at a higher temperature than comparable alkanes.

Carboxylic acids and amides that have a H on the nitrogen can also take part in hydrogen bonding, which plays a prominent role in their chemical, physical, and biochemical properties.

Two of the most common carboxylic acids are acetic acid and citric acid.

The portion of the carboxylic acid that does not change during a carbonyl-group substitution reaction is known as an acyl group.

The most significant property of carboxylic acids is their behaviour as weak acids. They surrender the hydrogen of the carboxyl group, ¬COOH, to bases and establish an acid-base equilibrium in aqueous solution.

If there are multiple functional groups present in a compound then according to the IUPAC, the priority of the functional group determines how the compound is named. That priority, from most important to least, is as follows:

• Carboxylic Acids>Esters>Amides>Aldehydes>Ketones>Alcohols>Thiols>Amines>Ethers>Alkenes>Alkynes>A-lkyl Halides>Alkanes

Compounds with a nitrogen directly attached to the carbonyl carbon atom are amides.

Properties of Carboxylic Acids, Esters, and Amides:

• All undergo carbonyl-group substitution reactions.

• Esters and amides are made from carboxylic acids.

• Esters and amides can be converted back to carboxylic acids.

• Carboxylic acids, primary amides, and secondary amides exhibit strong hydrogen bonding to one another; esters and tertiary amides do not hydrogen bond to one another. All carboxylic acids and their derivatives, however, can still hydrogen bond to water molecules.

• Simple acids and esters are liquids; all primary amides (except formamide) are solids.

• Carboxylic acids are weak acids and produce acidic aqueous solutions.

• Esters and amides are neither acids nor bases (pH neutral).

• Small (low-molecular-mass) amides are water-soluble, while small esters are slightly water-soluble.

• Volatile acids have strong, sharp odours while volatile esters have pleasant, fruity odours. Amides generally are odourless.

Carboxylate anion is the anion that results from ionization of a carboxylic acid, RCOO-

Carboxylic acids undergo neutralization reactions with bases in the same manner as other acids. With strong bases, such as sodium hydroxide, a carboxylic acid reacts to give water and a carboxylic acid salt.

Esterification is the reaction between an alcohol and a carboxylic acid to yield an ester plus water.

An ester is treated with water in the presence of a strong acid catalyst such as sulfuric acid, and hydrolysis takes place.

Saponification is the reaction of an ester with aqueous hydroxide ion to yield an alcohol and the metal salt (usually sodium or potassium) of a carboxylic acid.

Amides are extremely stable in water but do undergo hydrolysis with prolonged heating in the presence of acids or bases. The products are the carboxylic acid and amine from which the amide was synthesized.

Phosphoric acid is an inorganic acid with a striking resemblance to a carboxylic acid; it has three acidic hydrogen atoms, allowing it to form three different anions.

Phosphoric acid reacts with alcohols to form phosphate esters. It may be esterified at one, two, or all three of its ¬OH groups by reaction with an alcohol.

Polyesters and polyamides are formed when a dicarboxylic acid is allowed to react with either a dialcohol or a diamine, respectively. Dacron is an example of a polyester, while Nylon is an example of a polyamide. These polymers are used to make plastic bottles, recording tape, fabric etc.