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 hand, COOH is the molecular formula for a carboxyl group.
Carboxyl Group Examples
One of the best-known carboxyl group examples from carbon molecules 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 behavior 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, 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, \[CnH_{2}n+1COOH\]. 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 (\[CH_{3}COOH\].), methanoic acid (HCOOH), propanoic acid (\[C_{2}H_{5}COOH\].), and butanoic acid (\[C_{3}H_{7}COOH\].).
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 \[CH_{3}\] 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 exists 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 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 the 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 centers 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 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 are 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.
Did you know?
Carboxylic groups form bonds with each other due to their tendency to be stable in dimers
Acids participate in hydrogen bonding actively
Quick Summary
Tips & Trick to learn this Concept:
Organic concept and organic chemistry overall constitute a heavier weightage in chemistry as compared to inorganic chemistry.
It might seem difficult to learn at first glance but if studied thoroughly with practice, organic chemistry is good for scoring in exams.
The most important advice to study organic chemistry is not to learn it but to understand it
If any student is starting organic chemistry then he/ she must first start with the basic concepts. This followed by learning the nomenclature of the groups present in that compound, IUPAC names, and how to name them.
Later applications, synthesis, physical and chemical properties can be studied.
However, this studying must not be limited to just once, but until and unless the subject reaches a confident level, then these steps must be repeated while revising the subject.
The Acidity of Carboxylic Acids:
Carboxylic acid is the group of acids ranging from any number of compounds containing carbon and hydroxyl groups from any of the organic groups.
However Carboxylic acids are weak acids and they only partially dissociate into cations and anions.
The most acidic carboxylic acid is acetic acid followed by Benzoic acid and formic acid.
This list continues until trichloroacetic acid and trifluoroacetic acid.
Expected Questions
What is a carboxylic acid and how is it made?
Explain the physical properties of carboxylic acids.
Explain the chemical properties of carboxylic acids.
What are the uses of carboxylic acid?
What is the acidity of a carboxylic acid?
Explain amino acids in detail.
Does carboxylic acid have resonance structures?
FAQs on Carboxyl Group
1. What is a carboxyl group and what is its chemical formula?
A carboxyl group is a functional group in organic chemistry characterized by a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group. Its chemical formula is written as -COOH or -C(=O)OH. This unique combination of a carbonyl group (C=O) and a hydroxyl group (-OH) on the same carbon atom gives compounds containing it, known as carboxylic acids, their characteristic acidic properties.
2. What is the key difference between a carbonyl group and a carboxyl group?
The main difference lies in their structure and resulting chemical properties. A carbonyl group consists of a carbon atom double-bonded to an oxygen atom (C=O) and is characteristic of aldehydes and ketones. A carboxyl group (-COOH) is more complex; it contains a carbonyl group, but the same carbon atom is also bonded to a hydroxyl group (-OH). This addition of the hydroxyl group is what makes the carboxyl group acidic, a property the carbonyl group does not possess on its own.
3. How does a carboxyl group differ from a carboxylic acid?
This is a distinction between a part and a whole. The carboxyl group (-COOH) is the specific functional group. A carboxylic acid is the entire class of organic molecules that contains at least one carboxyl group attached to an alkyl (R) or aryl (Ar) group. For example, in acetic acid (CH₃COOH), the -COOH part is the carboxyl group, while the entire CH₃COOH molecule is a carboxylic acid.
4. Why are carboxylic acids acidic? Explain with the role of resonance.
Carboxylic acids are acidic because they can readily donate the proton (H⁺) from their hydroxyl (-OH) group. This acidity is significantly enhanced by the stability of the conjugate base formed after losing the proton, called the carboxylate ion (R-COO⁻). The stability of this ion comes from resonance. The negative charge is not located on a single oxygen atom; instead, it is delocalized, or spread out, across both oxygen atoms. This delocalization makes the carboxylate ion very stable, thus favouring the dissociation of the proton from the acid.
5. Why are carboxylic acids stronger acids than phenols and alcohols?
Carboxylic acids are stronger acids due to the superior stability of their conjugate base.
- In a carboxylate ion (R-COO⁻), the negative charge is delocalized over two highly electronegative oxygen atoms, which is a very stable arrangement.
- In a phenoxide ion (from phenol), the negative charge is delocalized over one oxygen atom and the less electronegative carbon atoms of the benzene ring. This is less stable than the carboxylate ion.
- In an alkoxide ion (from alcohol), the negative charge is localized on a single oxygen atom with no resonance stabilization, making it the least stable.
Because the carboxylate ion is the most stable, carboxylic acids are the most willing to donate a proton, making them the strongest acids among the three.
6. What are some important types of carboxylic acids with examples?
Carboxylic acids can be classified based on the group attached to the carboxyl functional group. Key types include:
- Aliphatic Carboxylic Acids: Where the carboxyl group is attached to an alkyl chain. Example: Acetic acid (CH₃COOH), found in vinegar.
- Aromatic Carboxylic Acids: Where the carboxyl group is attached to an aryl group like a benzene ring. Example: Benzoic acid (C₆H₅COOH), used as a food preservative.
- Dicarboxylic Acids: Compounds containing two carboxyl groups. Example: Adipic acid, a monomer used to produce nylon.
- Amino Acids: Molecules containing both a carboxyl group and an amino (-NH₂) group. Example: Glycine, a fundamental building block of proteins.
7. What is the importance of the carboxyl group in amino acids and proteins?
The carboxyl group is fundamental to the structure and function of amino acids and proteins. It serves two primary roles:
- It provides the 'acid' part of the amino acid, allowing it to act as an acid by donating a proton.
- Crucially, the carboxyl group of one amino acid reacts with the amino group of another to form a peptide bond (-CO-NH-). This covalent bond is the linkage that connects amino acids together in a chain, forming the primary structure of all proteins.
8. What is a real-world example of the carboxyl group's properties in action?
A common real-world example is vinegar, which is a dilute solution of acetic acid (CH₃COOH). The sharp, sour taste of vinegar is a direct result of the acidic nature of the carboxyl group, which releases hydrogen ions (protons) in the solution. Another example is the use of sodium benzoate, the salt of benzoic acid, as a food preservative. Its ability to inhibit the growth of mould and yeast is due to the properties conferred by its carboxyl group.
