Carboxyl acids and their derivatives
The organic compounds having a carboxyl group are acidic and are termed as carboxylic acids.
The general molecular formula is CnH2n+1COOH.
Nomenclature of Carboxylic acids
Carboxylic acids containing one, two or three carboxyl groups are known as mono, di and tri
carboxylic acids. This may be aliphatic, alicyclic and aromatic. These may be further subdivided into
saturated, unsaturated and substituted e.g. hydroxyl, nitro, amino and halo carboxylic acids.
Monocarboxylic acids
Dicarboxylic acid
The aliphatic monocarboxylic acids are known as fatty acids, as many of these acids (especially the
higher members) found in fats, in the form of glyceryl esters.
Monocarboxylic acids are named according to the following systems of nomenclature:
1. Trivial name: Common or trivial names of lower members were derived from their source of
occurrence.
Formula Source Trivial name
HCOOH Red ant (Formica) Formic acid
CH3COOH Vineger (Acetum) Acetic acid
CH3CH2CH2COOH Butter (Butyrum) Butyric acid
CH3(CH2)3COOH Valerian plant root Valeric acid
The position of the substituent present on the chain is specified by the Greek letters and α, β, γ, σ
and so on. The carbon atom next to the carboxyl group is considered as α.
1
,2. IUPAC names: They are derived from the IUPAC names of the corresponding hydrocarbons by
removing the terminal “e” by “oic acid”.
Formula IUPAC Trivial name
HCOOH Methanoic acid Formic acid
CH3COOH Ethanoic acid Acetic acid
CH3CH2COOH Propanoic acid Propanoic acid
CH3CH2CH2COOH Butanoic acid Butyric acid
CH3(CH2)3COOH Pentanoic acid Valeric acid
CH3(CH2)4COOH Hexanoic acid Caproic acid
The generic IUPAC name of acids derived are from alkanes (saturated aliphatic hydrocarbons) is
alkanoic acids. Similarly, alkenoic acids and alkynoic acids are generic names of acids derived
from unsaturated aliphatic hydrocarbons alkenes and alkynes respectively.
The position of the double/triple bonds, side chains and/or substituents are indicated by appropriate
Arabic numerals.
Acidity of carboxylic acids
1. Carboxylic acids are acidic due to their ability to release H+ (proton) in solution.
2. Carboxylic acid is stabilized by resonance. The acidic character of carboxylic acids is due to
resonance in the acidic group which imparts electron deficiency (positive charge) on the oxygen
atom of the hydroxyl group.
In resonance structure II the positive charge on oxygen atom causes a displacement of electron pair of
the O-H bond towards the oxygen atom, with the result, the hydrogen atom of the O-H group is
eliminated as proton (H+) and a carboxylate ion is formed. Once the carboxylate ion is formed, it is
stabilised by resonance.
2
, Due to equivalent resonating structures, resonance in carboxylate anion is more important than in the
parent carboxylic acid. Hence carboxylate anion is more stabilised than the acid itself and hence the
equilibrium of the ionisation of acids shifts to the right hand side which explains acidity.
Effect of substituents on acidity of aliphatic acids
The carboxylic acids are acidic in nature because of stabilisation (i.e. dispersal of negative charge) of
carboxylate ion. So any factors which can enhance the dispersal of negative charge of the carboxylate
ion will increase the acidity and vice versa. Thus electron withdrawing substances (like halogens, -NO2,
-C6H5) would disperse the negative charge and stabilise the carboxylate ion and thus increase the acidity
of the parent acid. On the other hand, electron releasing substances (e.g., -CH3, -OH, -OCH3 etc) would
increase the negative charge, destabilise the carboxylate ion thus decrease acidity of the parent acid.
Now since alkyl groups are electron releasing groups, their presence in the molecule will decrease the
acidity. In general, greater the length of the alkyl chain, lower shall be the acidity of the acid. Thus
formic acid (HCOOH), having no alkyl group, is about 10 times stronger than acetic acid (CH3COOH)
which in turn stronger than propanoic acid (CH3CH2COOH) and so on. Similarly, following order is
observed in chloroacetic acids.
Chloro Group (-Cl) is electron withdrawing in nature. It helps in dispersal of –ve charge and stabilized
the carboxylate ion. Greater the number of halogen atoms, greater will be the extent of stabilization and
the acidity
Benzoic acid is somewhat stronger than simple aliphatic acid. Here the carboxylate group is attached to
a more electronegative carbon (sp2 hybridised) than in aliphatic acids (sp3 hybridised). In addition to that
phenyl group (-C6H5) is electron withdrawing.
It may be recalled that electronegative substituents have an inductive acid strengthening effect in the
case of aliphatic carboxylic acids. Electropositive group decrease the acidity. The resonance stabilisation
of the carboxylate anion results in increased acidity of the acid.
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The organic compounds having a carboxyl group are acidic and are termed as carboxylic acids.
The general molecular formula is CnH2n+1COOH.
Nomenclature of Carboxylic acids
Carboxylic acids containing one, two or three carboxyl groups are known as mono, di and tri
carboxylic acids. This may be aliphatic, alicyclic and aromatic. These may be further subdivided into
saturated, unsaturated and substituted e.g. hydroxyl, nitro, amino and halo carboxylic acids.
Monocarboxylic acids
Dicarboxylic acid
The aliphatic monocarboxylic acids are known as fatty acids, as many of these acids (especially the
higher members) found in fats, in the form of glyceryl esters.
Monocarboxylic acids are named according to the following systems of nomenclature:
1. Trivial name: Common or trivial names of lower members were derived from their source of
occurrence.
Formula Source Trivial name
HCOOH Red ant (Formica) Formic acid
CH3COOH Vineger (Acetum) Acetic acid
CH3CH2CH2COOH Butter (Butyrum) Butyric acid
CH3(CH2)3COOH Valerian plant root Valeric acid
The position of the substituent present on the chain is specified by the Greek letters and α, β, γ, σ
and so on. The carbon atom next to the carboxyl group is considered as α.
1
,2. IUPAC names: They are derived from the IUPAC names of the corresponding hydrocarbons by
removing the terminal “e” by “oic acid”.
Formula IUPAC Trivial name
HCOOH Methanoic acid Formic acid
CH3COOH Ethanoic acid Acetic acid
CH3CH2COOH Propanoic acid Propanoic acid
CH3CH2CH2COOH Butanoic acid Butyric acid
CH3(CH2)3COOH Pentanoic acid Valeric acid
CH3(CH2)4COOH Hexanoic acid Caproic acid
The generic IUPAC name of acids derived are from alkanes (saturated aliphatic hydrocarbons) is
alkanoic acids. Similarly, alkenoic acids and alkynoic acids are generic names of acids derived
from unsaturated aliphatic hydrocarbons alkenes and alkynes respectively.
The position of the double/triple bonds, side chains and/or substituents are indicated by appropriate
Arabic numerals.
Acidity of carboxylic acids
1. Carboxylic acids are acidic due to their ability to release H+ (proton) in solution.
2. Carboxylic acid is stabilized by resonance. The acidic character of carboxylic acids is due to
resonance in the acidic group which imparts electron deficiency (positive charge) on the oxygen
atom of the hydroxyl group.
In resonance structure II the positive charge on oxygen atom causes a displacement of electron pair of
the O-H bond towards the oxygen atom, with the result, the hydrogen atom of the O-H group is
eliminated as proton (H+) and a carboxylate ion is formed. Once the carboxylate ion is formed, it is
stabilised by resonance.
2
, Due to equivalent resonating structures, resonance in carboxylate anion is more important than in the
parent carboxylic acid. Hence carboxylate anion is more stabilised than the acid itself and hence the
equilibrium of the ionisation of acids shifts to the right hand side which explains acidity.
Effect of substituents on acidity of aliphatic acids
The carboxylic acids are acidic in nature because of stabilisation (i.e. dispersal of negative charge) of
carboxylate ion. So any factors which can enhance the dispersal of negative charge of the carboxylate
ion will increase the acidity and vice versa. Thus electron withdrawing substances (like halogens, -NO2,
-C6H5) would disperse the negative charge and stabilise the carboxylate ion and thus increase the acidity
of the parent acid. On the other hand, electron releasing substances (e.g., -CH3, -OH, -OCH3 etc) would
increase the negative charge, destabilise the carboxylate ion thus decrease acidity of the parent acid.
Now since alkyl groups are electron releasing groups, their presence in the molecule will decrease the
acidity. In general, greater the length of the alkyl chain, lower shall be the acidity of the acid. Thus
formic acid (HCOOH), having no alkyl group, is about 10 times stronger than acetic acid (CH3COOH)
which in turn stronger than propanoic acid (CH3CH2COOH) and so on. Similarly, following order is
observed in chloroacetic acids.
Chloro Group (-Cl) is electron withdrawing in nature. It helps in dispersal of –ve charge and stabilized
the carboxylate ion. Greater the number of halogen atoms, greater will be the extent of stabilization and
the acidity
Benzoic acid is somewhat stronger than simple aliphatic acid. Here the carboxylate group is attached to
a more electronegative carbon (sp2 hybridised) than in aliphatic acids (sp3 hybridised). In addition to that
phenyl group (-C6H5) is electron withdrawing.
It may be recalled that electronegative substituents have an inductive acid strengthening effect in the
case of aliphatic carboxylic acids. Electropositive group decrease the acidity. The resonance stabilisation
of the carboxylate anion results in increased acidity of the acid.
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