Carboxyl Group

What Is A Carboxyl Group?

A carboxyl group is a very common functional group that is defined as having a carbonyl and hydroxyl group linked to a carbon atom through a single bond. Similarly, an organic compound containing a carboxyl group is referred to as a carboxylic acid. Just to remember, a carbonyl group is a carbon double-bonded to oxygen, and a hydroxyl group is an OH group. 

While working with a carboxyl group, we need to be on the lookout for two things: a carbon and an OH double-bonded to oxygen. But, better, if we consider the word carboxyl, we can split it down into two parts as 'carb' and 'oxyl.' Seeing 'carb,' we think of the carbon atom. Whereas, seeing '-oxyl,' we think about the hydroxyl group. On the other side, COOH is the molecular formula for a carboxyl group.

Carboxyl Group Examples

One of the best-known carboxyl group examples from carbon molecule is a carboxylic acid. The carboxylic acid’s general formula is R-C(O)OH. Where R defines any number of chemical species. Carboxylic acids are found in amino acids and acetic acids that are used to build proteins.

Because the hydrogen ion detaches behaviour so readily, most commonly, the molecule is found as a carboxylate anion R-COO-. With the help of the suffix “-ate,” the anion is named. For example, the acetic acid (a carboxylic acid) becomes an acetate ion.

Carboxyl Group Formula

Carboxylic acids are a homologous series where the compounds contain a functional group known as a carboxyl group (-COOH). The general carboxyl group molecular formula will be, CnH2n+1COOH. Carboxylic acids contain a minimum of one carboxyl group. The acids with two or more carboxyl groups attached are referred to as dicarboxylic acids, tricarboxylic acids, and so on. Also, carboxylic acids are the derivatives of hydrocarbons where a carboxyl group has replaced one or more to that of the hydrogen atoms in the hydrocarbon. The carboxylic acids (first four) derived from alkanes are ethanoic acid (CH3COOH), methanoic acid (HCOOH), propanoic acid (C2H5COOH), and butanoic acid (C3H7COOH).

The carboxyl group structure for all the above mentioned carboxylic acids is given below.

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Nomenclature of Carboxylic Acids

If either the compound or the primary carbon skeleton is acyclic, name the alkane for the system that would occur if the carboxylic acid were a CH3 group. Then drop the terminal ‘-e’ by substituting “-oic” acid.  The carbon present in the carboxylic acid group is always carbon 1 (this can make different numbers from that of the alkane).

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If the other structural feature overrides the carboxylic acid (suppose, a ring), a suffix “-carboxylic” acid will be added to a root name taken by excluding the carbon atom of carboxylic acid. The carboxylic acid again defines the numbering, but now C-1 is the carbon, bearing with the COOH group.

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Structure of Carboxyl Group

Carboxyl groups exist on the side of a molecule. It ionizes, discharging the Hydrogen (H) from the hydroxyl aggregate as a free proton (H+), with the rest of the Oxygen (O) conveying a negative (-ve) charge. This charge turns to forward and backward between the two oxygen molecules, which makes this ionized state steady moderately.

The 3D ball structure of a carboxyl group is represented below.

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Properties of Carboxyl Group

Few of the properties of carboxyl group are listed below.

  • The Carboxyl group contains a double bond of electronegative oxygen to a carbon atom. As a result, the polarity of a bond will increase.

  • A compound containing a carboxyl group should possess hydrophilic centres with a high melting point and boiling point.

  • The reason behind the high melting and boiling point may be dissipated by creating a hydrogen bond in the solid-state and liquid state. Another typical example is fatty acids.

Carboxyl Group From Nature

Acetic acid can be naturally blended by an anaerobic fermentation, which is the procedure used to produce vinegar. The rigorous approach includes warm ethanol and Acetobacter oxygen. The anaerobic process requires only sugar as an input chemical, and acetogen will then yield carboxylic acids. It should be noticed that the high-impact process is still mostly connected because the acetogenins utilized for anaerobic procedures by indicating less resistance to acidic situations. Ultimately, acetogenesis will be destroyed if a large quantity of acids is produced to a great volume.

Benzoic acid is a fundamental element of benzoin resin. Genuinely, it is expensive to remove benzoic acid, primarily from benzoin resins. Most of the benzoic acid found in the market is manufactured mechanically along these lines.

Uses of Carboxylic Acids

  • Methanoic is the acid used in rubber, textile, dyeing, leather, and electroplating industries.

  • Acetic acid is used as a solvent and as vinegar in the food industry.

  • Hexanedioic acid is used in the manufacturing of nylon-6, 6, which is a commercially important polymer.

  • Esters of benzoic acid are used in perfume making industries.

  • Sodium Benzoate is also used as a preservative.

  • Higher fatty acids are used in the manufacturing of detergents and soaps.

FAQ (Frequently Asked Questions)

1. Why are carboxylic acids more acidic than phenol?

The acidity of a carboxylic acid is higher compared to alcohol and phenols because, carboxylate ion, the conjugate base of the carboxylic acid is stabilized by two equivalent resonance structures where the negative charge is effectively delocalized between two more electronegative oxygen atoms.

On the other side, considering phenols, a negative charge is delocalized less strongly on one oxygen atom and also less electronegative carbon atoms in phenoxide ions. The carboxylate ion is, therefore, more stable compared to the phenoxide ion. Carboxylic acids are also more acidic than phenols.

2. Why are the carboxylic acids stronger acids compared to alcohol?

It is because of electronegativity. For Bronsted acids (such as alcohols and carboxylic acids), an acid is stronger when its tendency to release a proton is strong.

For both carboxylic acid and alcohol, there is hydrogen covalently bound to an oxygen (but not exactly true because for the carboxylic acid, the bond is spread out between the two oxygens).

Also, oxygen is more electronegative than hydrogen. It means that oxygen is an electron-withdrawing. If we withdraw the electrons from the covalent bond to hydrogen, we get a hydrogen ion (which is a proton).

To make it simple, because two oxygens (carboxylic acid) are more electron-withdrawing than one oxygen (alcohol), generally, they have a larger tendency to “release” the proton, i.e., they are stronger acids.