Category: Chemistry

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Nitro Compounds

Nitro compounds are considered as the derivaties of hydrocarbons. If one of the hydrogen atom of hydrocarbon is replaced by the – NO₂ group, the resultant organic compound is called a nitrocompound.

Classification of Nitrocompounds

Nitroalkanes are represented by the formula, R-NO₂ where R is an alkyl group (C_nH_2n+1-). Nitroalkanes are further classified into primary, secondary, tertiary nitroalkanes on the basis of type of carbon atom to which the nitro (-NO₂) group is attached.

Nomenclature of Nitroalkanes

In the IUPAC nomenclature, the nitroalkanes are named by adding prefi nitro before the name of alkane, the position of the nitro group is indicated by number.

ISOMERISM

Nitroalkanes exhibit chain and position isomerism among their own class and functional isomerism with alkyl nitrites and special type tautomerism can also exist in nitro alkanes having an α – H atom. For example, nitro compounds having the molecular formula C₄H₉NO₂ exhibit the following isomerisms.

Tautomerism:

Primary and secondary nitroalkanes, having α-H, also show an equilibrium mixture of two tautomers namely nitro – and aci – form.

Tertiary nitro alkanes do not exhibit tautomerism due to absence of α – H atom.

Nitro Form	Aci-Form
1. Less Acidic	1. More Acidic
2. Dissolves in NaOH slowly	2. Dissolves in NaOH instantly
3. Decolourises FeCl3 solution	3. With FeCl3 gives reddish brown colour
4. Electrical conductivity is low	4. Electrical conductivity is high

Acidic Nature of Nitro Alkanes

Th α – H atom of 1° & 2° nitroalkanes show acidic character because of the electron with drawing effect of NO₂ group. These are more acidic than aldehydes, ketones, ester and cyanides. Nitroalkanes dissolve in NaOH solution to form a salt. Aci – nitro derivatives are more acidic than nitro form. When the number of alkyl group attached to α carbon increases, acidity decreases. due to +I effect of alkyl groups.

Preparation of Nitroalkanes

1. From Alkyl Halides: (Laboratory Method)

(a) Alkyl bromides (or) iodides on heating with ethanolic solution of potassium nitrite gives nitroethane.

The reaction follows SN₂ mechanism.

This method is not suitable for preparing nitrobenzene because the bromine directly attached to the benzene ring cannot be cleaved easily.

2. Vapour Phase Nitration of Alkanes: (Industrial Method)

Gaseous mixture of methane and nitric acid passed through a red hot metal tube to give nitromethane.

Except methane, other alkanes (upto n – hexane) give a mixture of nitroalkanes due to C-C cleavage. The individual nitro alkanes can be separated by fractional distillation.

3. From α – Halocarboxylic Acid

α – choloroacetic acid when boiled with aqueous solution of sodium nitrite gives nitromethane.

4. Oxidation of Tert – Alkyl Amines

tert – butyl amine is oxidised with aqueous KMnO₄ to give tert – nitro alkanes.

5. Oxidation of Oximes

Oxidation of acetaldoxime and acetoneoxime with trifloroperoxy acetic acid gives nitroethane (1°) and 2 – nitropropane (2°) respectively.

Preparation of Nitroarenes

1. By Direct Nitration

When benzene is heated at 330K with a nitrating mixture (Con.HNO₃ + Con.H₂SO₄), electrophilic
substitution takes place to form nitro benzene. (Oil of mirbane)

On direct nitration of nitrobenzene m – dinitrobenzene is obtained

2. Indirect Method

Nitration of nitro benzene gives m-dinitrobenzene. The following method is adopted for the preparation of p-dinitrobenzene.

For example

Amino group can be directly converted into nitro group, using caro’s acid (H₂SO₅) (or) persulphuric acid
(H₂S₂O₈) (or) peroxytrifluro acetic acid (F₃C.CO₃H) as oxidising agent.

Physical Properties of Nitro Alkane

The lower nitroalkanes are colourless pleasant smelling liquids, sparingly soluble in water, but readily soluble in organic solvents like benzene, acetone etc… They have high boiling points because of their highly polar nature. Alkylnitrites have lower boiling points than nitro alkanes.

Chemical Properties of Nitroalkanes

Nitroalkanes undergo the following common reactions.

1. Reduction
2. Hydrolysis
3. Halogenations

1. Reduction of Nitroalkanes

Reduction of nitroalkanes has important synthetic applications. The various reduction stages of nitro group are given below.

The final product depends upon the nature of reducing agent as well as the pH of the medium.

Reduction of Alkyl Nitrites

Ethylnitrite on reduction with Sn / HCl gives ethanol

2. Hydrolysis of Nitroalkanes

Hydrolysis can be effected using conc. HCl or conc. H₂SO₄. Primary nitroalkanes on hydrolysis gives carboxylic acid, and the secondary nitroalkanes give ketones. The tertiary nitroalkanes have no reaction.

On the other hand, the acid or base hydrolysis of ethyl nitrite gives ethanol.

3. Halogenation of Nitroalkanes

Primary and secondary nitroalkanes on treatement with Cl₂ or Br₂ in the presence of NaOH give halonitroalkanes. The α – H atom of nitroalkanes are successively replaced by halogen atoms.

Toxicity

Nitroethane is suspected to cause genetic damage and be harmful to the nervous system.

Nef Carbonyl Synthesis:

Chemical Properties of Nitrobenzene

Electrolytic Reduction:

Reduction of Catalytic and Metal Hydrides

Nitrobenzene reduction with Ni (or) Pt, (or) LiAlH₄ to give aniline

Selective Reduction of Polynitro Compounds

Electrophilic Substitution Reaction

The electrophilic substitution reactions of nitrobenzene are usually very slow and vigorous reaction condition have to be employed (-NO₂ group is strongly deactivating and m – directing).

Nitrobenzene does not undergo Friedel – Craft reactions due to the strong deactivating nature of -NO₂ group.

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Uses of Carboxylic Acids and its Derivatives

Formic Acid

It is Used

1. For the dehydration of hides.
2. As a coagulating agent for rubber latex
3. In medicine for treatment of gout
4. As an antiseptic in the preservation of fruit juice.

Acetic Acid

It is Used

1. As table vinegar
2. For coagulating rubber latex
3. For manufacture of cellulose acetate and poly vinylacetate

Benzoic Acid

It is Used

1. As food preservative either in the pure form or in the form of sodium benzoate
2. In medicine as an urinary antiseptic
3. For manufacture of dyes

Acetyl Chloride

It is Used

1. As acetylating agent in organic synthesis
2. In detection and estimation of – OH, – NH₂ groups in organic compounds

Acetic Anhydride

It is Used

1. Acetylating Agent
2. In the preparation of medicine like asprin and phenacetin
3. For the manufacture plastics like cellulose acetate and poly vinyl acetate.

Ethyl Acetate is Used

1. In the preparation of artificial fruit essences.
2. As a solvent for lacquers.
3. In the preparation of organic synthetic reagent like ethyl acetoacetate.

Carboxylic acids and their derivatives are used in the production of polymers, biopolymers, coatings, adhesives, and pharmaceutical drugs. They also can be used as solvents, food additives, antimicrobials, and flavourings.

The functional groups at the heart of this chapter are called carboxylic acid derivatives: they include carboxylic acids themselves, carboxylates (deprotonated carboxylic acids), amides, esters, thioesters, and
acyl phosphates.

Carboxylic acids have a hydroxyl group bonded to an acyl group, and their functional derivatives are prepared by replacement of the hydroxyl group with substituents, such as halo, alkoxyl, amino and acyloxy. Some examples of these functional derivatives were displayed earlier.

Carboxylic acids are also important in the manufacture of greases, crayons, and plastics. Compounds with carboxyl groups are relatively easily converted to compounds called esters, which have the hydrogen atom of the carboxyl group replaced with a group containing carbon and hydrogen atoms.

In general, it finds use primary as an acylating agent (source of an acetyl group) for alcohols and amines. This liquid is also used to make pharmaceuticals such as aspirin and salicylic acid, as well as a preservative for wood.

Carboxylic acids are soluble in water. Carboxylic acids do not dimerise in water, but forms hydrogen bonds with water. Carboxylic acids are polar and due to the presence of the hydroxyl in the carboxyl group, they are able to form hydrogen bonds with water molecules.

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Functional Derivatives of Carboxylic Acids

Compounds such as acid chlorides, amides, esters etc., are called carboxylic acid derivatives because they differ from a carboxylic acid only in the nature of the group or atom that has replaced the – OH group of carboxylic acid.

Relative Reactivity of Acid Derivatives

The reactivity of the acid derivatives follows the order

The above order of reactivity can be explained in terms of

1. Basicity of the leaving group
2. Resonance effect

1. Basicity of the Leaving Group

Weaker bases are good leaving groups. Hence acyl derivatives with weaker bases as leaving groups (L) can easily rupture the bond and are more reactive. The correct order of the basicity of the leaving group is . Hence the reverse is the order of reactivity.

2. Resonance Effect

Lesser the electronegativity of the group, greater would be the resonance stabilization as shown below. This effect makes the molecule more stable and reduces the reactivity of the acyl compound. The order of electronegativity of the leaving groups follows the order – Cl > – OCOR > – OR > – NH₂

Hence the order of reactivity of the acid derivatives with nucleophilic reagent follows the order

acid halide > acid anhydride > esters > acid amides

Nomenclature

Acid Halides:

Methods of Preparation of Acid Chloride:

Acid chlorides are prepared from carboxylic acid by treating it with anyone of the chlorinating agent such as SOCl₂, PCl₅, or PCl₃

1. By Reaction with Thionyl Chloride (SOCl₂)

This method is superior to others as the by products being gases escape leaving the acid chloride in the pure state.

Physical Properties:

• They emit pale fumes of hydrogen chloride when exposed to air on account of their reaction with water vapour.
• They are insoluble in water but slowly begins to dissolve due to hydrolysis.

Chemical Properties:

They react with weak nucleophiles such as water, alcohols, ammonia and amines to produce the corresponding acid, ester, amide or substituted amides.

1. Hydrolysis:

Acyl halides undergo hydrolysis to form corresponding carboxylic acids

2. Reaction with Alcohols (Alcoholysis) gives esters.

3. Reaction with Ammonia (Ammonolysis) gives acid amides.

4. Reaction with 1° and 2° Amines gives N-alkyl amides.

5. Reduction

(a) When reduced with hydrogen in the presence of ‘poisoned’ palladium catalyst, they form aldehydes. This reaction is called Rosenmund reduction. We have already learnt this reaction under the preparation of aldehydes.

(b) When reduced with LiAlH₄ gives primary alcohols.

Acid Anhydride

Methods of Preparation

1. Heating carboxylic acid with P₂O₅

We have already learnt that when carboxylic acids are heated with P₂O₅ dehydration takes place to form
acid anhydride.

2. By Reaction of Acid Halide With a Salt of Carboxylic Acids

Acid chlorides on heating with sodium salt of carboxylic acids gives corresponding anhydride.

Chemical Properties

1. Hydrolysis

Acid anhydride are slowly hydrolysed, by water to form corresponding carboxylic acids.

2. Reaction With Alcohol

Acid anhydride reacts with alcohols to form esters.

3. Reaction With Ammonia

Acid anhydride reacts with ammonia to form amides.

4. Reaction with PCl₅

Acid anhydride reacts with PCl₅ to form acyl chlorides.

Esters

Methods of Preparation

1. Esterification

We have already learnt that treatment of alcohols with carboxylic acids in presence of mineral acid gives esters. The reaction is carried to completion by using an excess of reactant or by removing the water from the reaction mixture.

2. Alcoholysis of Acid Chloride or Acid Anhydrides

(ii) Treatment of acid chloride or acid anhydride with alcohol also gives esters.

Physical Properties

Esters are colour less liquids or solids with characteristic fruity smell. Flavours of some of the esters are given below.

Ester	Flavour
1. Amyl acetate	Banana
2. Ethyl butyrate	Pineapple
3. Octyl acetate	Orange
4. Isobutyl formate	Raspberry
5. Amyl butyrate	Apricot

Chemical Properties

They react with weak nucleophiles such as water, alcohols, ammonia and amines to produce the corresponding acid, ester, amide or substituted amides.

1. Hydrolysis

We have already learnt that hydrolysis of esters gives alcohol and carboxylic acid.

2. Reaction With Alcohol (Transesterification)

Esters of an alcohol can react with another alcohol in the presence of a mineral acid to give the ester of second alcohol. The interchange of alcohol portions of the esters is termed transesterification.

 Transesterification

3. Reaction With Ammonia (Ammonolysis)

Esters react slowly with ammonia to form amides and alcohol.

4. Claisen Condensation

Esters containing at least one ∝ – hydrogen atom undergo self condensation in the presence of a strong base such as sodium ethoxide to form β – keto ester.

5. Reaction with PCl₅

Esters react with PCl₅ to give a mixture of acyl and alkyl chloride

Acid Amides

Acid amides are derivatives of carboxylic acid in which the – OH part of carboxyl group has been replaced by – NH₂ group. The general formula of amides are given as follows image 21 Now, we shall focus our attention mainly on the study of chemistry of acetamide.

Methods of Preparation

1. Ammonolysis of Acid Derivatives

Acid amides are prepared by the action of ammonia with acid chlorides or acid anhydrides.

2. Heating Ammonium Carboxylates

Ammonium salts of carboxylic acids (ammonium carboxylates) on heating, lose a molecule of water to form amides.

3. Partial Hydrolysis of Alkyl Cyanides (Nitriles)

Partial hydrolysis of alkyl cyanides with cold con HCl gives amides

Chemical Properties

1. Amphoteric Character

Amides behave both as weak acid as well as weak base and thus show amphoteric character. This can be proved by the following reactions.

Acetamide (as acid) reacts with sodium to form sodium salt and hydrogen gas is liberated. 

3. Dehydration

Amides on heating with strong dehydrating agents like P₂O₅ get dehydrated to form cyanides.

4. Hof Mann’s Degradation

Amides reacts with bromine in the presence of caustic alkali to form a primary amine carrying one carbon less than the parent amide.

5. Reduction

Amides on reduction with LiAlH₄ or Sodium and ethyl alcohol to form corresponding amines.

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Acidity of Carboxylic Acids

Carboxylic acids undergo ionisation to produce H⁺ and carboxylate ions in aqueous solution. The carboxylate anion is stabilised by resonance which make the Carboxylic acid to donate the proton easily.

The resonance structure of carboxylate ion are given below.

The strength of carboxylic acid can be expressed in terms of the dissociation constant(Ka):

The dissociation constant is generally called acidity constant because it measures the relative strength of an acid. The stronger the acid, the higher will be its Ka value.

The dissociation constant of an acid can also be expressed in terms of pKa value.

pKa = – log Ka

A stronger acid will have higher Ka value but smaller pKa value.

Ka and pKa values of some Carboxylic acids of 298 K

Effect of substituents on the acidity of carboxylic acid.

(i) Electron Releasing Alkyl Group Decreases the Acidity

Th electron releasing groups (+I groups) increase the negative charge on the carboxylate ion and destabilise it and hence the loss of proton becomes difficult. For example, formic acid is more stronger than acetic acid.

(ii) Electron with Drawing Substituents Increases the Acidity

The electron – withdrawing substituents decrease the negative charge on the carboxylate ion and stabilize it. In such cases, the loss of proton becomes relatively easy. Acidity increases with increasing electronegativity of the substituents. For example, the acidity of various halo acetic acids follows the order

F – CH₂ – COOH > Cl – CH₂ COOH > Br – CH₂ – COOH > I – CH₂ – COOH

Acidity increases with increasing number of electron – withdrawing substituents on the α – carbon. For example

Cl₃C – COOH > Cl₂CH – COOH > ClCH₂COOH > CH₃COOH

The effect of various, electron withdrawing groups on the acidity of a carboxylic acid follows the order,

– NO₂ > – CN > – F > – Cl > – Br > – I > Ph

The relative acidities of various organic compounds are

RCOOH > ArOH > H₂O > ROH > RC ≡ CH

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Chemical Properties of Carboxylic Acids

Carboxylic acid do not give the characteristic reaction of carbonyl group image 1 as given by the aldehydes and ketones. as the carbonyl group of carboxylic acid is involved in resonance:

The reactions of carboxylic acids can be classified as follows:

(A) Reactions involving cleavage of O – H bond.
(B) Reactions involving cleavage of C – OH bond.
(C) Reactions involving – COOH group.
(D) Substitution reactions involving hydrocarbon part.

(A) Reactions involving cleavage of O – H bond.

1. Reactions with Metals

Carboxylic acid react with active metals like Na, Mg, Zn etc to form corresponding salts with the liberation of hydrogen.

Example

2. Reaction with Alkalies

Carboxylic acid reacts with alkalies to neutralise them and form salts.

Example

3. Reaction with Carbonates and Bicarbonates (Test for Carboxylic Acid Group)

Carboxylic acids decompose carbonates and bicarbonates evolving carbondioxide gas with effervescence.

Example

4. All Carboxylic Acids Turn Blue Litmus Red

(B) Reactions involving cleavage of C-OH bond

1. Reactions with PCl₅, PCl₃ and SOCl₂

Example

2. Reactions with Alcohols (Esterification)

When carboxylic acids are heated with alcohols in the presence of conc. H₂SO₄ or dry HCl gas, esters are formed. The reaction is reversible and is called esterification.

Example

Mechanism of Esterification:

The Mechanism of esterifiation involves the following steps.

(C) Reactions involving – COOH group

1. Reduction

(i) Partial Reduction to Alcohols

Carboxylic acids are reduced to primary alcohols by LiAlH₄ or with hydrogen in the presence of copper chromite as catalyst. Sodium borohydride does not reduce the – COOH group.

Example

(ii) Complete Reduction to Alkanes

When treated with HI and red phosphorous, carboxylic acid undergoes complete reduction to yield alkanes containing the same number of carbon atoms.

Example

2. Decarboxylation

Removal of CO₂ from carboxyl group is called as decarboxylation. Carboxylic acids lose carbon dioxide to form hydrocarbon when their sodium salts are heated with soda lime (NaOH and CaO in the ratio 3:1)

Example

3. Kolbe’s Electrolytic Decarboxylation

The aqueous solutions of sodium or potassium salts of carboxylic acid on electrolysis gives alkanes at anode. This reaction is called kolbes electrolysis.

Sodium formate solution on electrolysis gives hydrogen

4. Reactions with Ammonia

Carboxylic acids react with ammonia to form ammonium salt which on further heating at high temperature gives amides.

Example

5. Action of Heat in the Presence of P₂O₅

Carboxylic acid on heating in the presence of a strong dehydrating agent such as P₂O₅ forms acid anhydride.

Example

(D) Substitution Reactions in the Hydrocarbon Part

1. α – Halogenation

Carboxylic acids having an α – hydrogen are halogenated at the α – position on treatment with chlorine or bromine in the presence of small amount of red posphorus to form α halo carboxylic acids. This reaction is known as Hell – Volhard – Zelinsky reaction (HVZ reaction). The α – Halogenated acids are convenient starting materials for preparing α – substituted acids.

2. Electrophilic Substitution in Aromatic Carboxylic Acids

Aromatic carboxylic acid undergoes electrophilic substitution reactions. The carboxyl group is a deactivating and meta directing group. Some common electrophilic substitution reactions of benzoic acid are given below.

(i) Halogenation

(ii) Nitration

(iii) Sulphonation

(iv) Benzoic acid does not undergo friedal crafts reaction. This is due to the strong deactivating nature of the carboxyl group.

(E) Reducing Action of Formic Acid

Formic acid contains both an aldehyde as well as an acid group. Hence, like other aldehydes, formic acid can easily be oxidised and therefore acts as a strong reducing agent

(i) Formic acid reduces Tollens reagent (ammonical silver nitrate solution) to metallic silver.

(ii) Formic acid reduces Fehlings solution. It reduces blue coloured cupric ions to red coloured cuprous ions.

Tests for Carboxylic Acid Group

1. In aqueous solution carboxylic acid turn blue litmus red.
2. Carboxylic acids give brisk effervescence with sodium bicarbonate due to the evolution of carbon-di-oxide.
3. When carboxylic acid is warmed with alcohol and Con H₂SO₄ it forms an ester, which is detected by its fruity odour.

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Physical Properties of Carboxylic Acids

1. Aliphatic carboxylic acid upto nine carbon atoms are colour less liquids with pungent odour. The higher members are odourless wax like solids.

2. Carboxylic acids have higher boiling point than aldehydes, ketones and even alcohols of comparable molecular masses. This is due to more association of carboxylic acid molecules through intermolecular hydrogen bonding.

In fact, most of the carboxylic acids exist as dimer in its vapour phase.

3. Lower aliphatic carboxylic acids (up to four carbon) are miscible with water due to the formation of hydrogen bonds with water. Higher carboxylic acid are insoluble in water due to increased hydrophobic interaction of hydrocarbon part. The simplest aromatic carboxylic acid, benzoic acid is insoluble in water.

4. Vinegar is 6 to 8% solution of acetic acid in water. Pure acetic acid is called glacial acetic acid. Because it forms ice like crystal when cooled. When aqueous acetic acid is cooled at 289.5 K, acetic acid solidifies and forms ice like crystals, where as water remains in liquid state and removed by filtration. This process is repeated to obtain glacial acetic acid.

• Carboxylic acids have high boiling points compared to other substances of comparable molar mass. Boiling points increase with molar mass.
• Carboxylic acids having one to four carbon atoms are completely miscible with water. Solubility decreases with molar mass.

Carboxylic acids are soluble in water. Carboxylic acids do not dimerise in water, but forms hydrogen bonds with water. Carboxylic acids are polar and due to the presence of the hydroxyl in the carboxyl group, they are able to form hydrogen bonds with water molecules.

The solubility of compounds containing the carboxyl functional group in water depends on the size of the compound. The smaller the compound (the shorter the R group), the higher the solubility. The boiling point of a carboxylic acid is generally higher than that of water.

Larger carboxylic acids are solids with low melting points. There are a great many aromatic carboxylic acids, which are all crystalline solids. Carboxylic acids can form intermolecular hydrogen bonds and thus have relatively high melting and boiling points compared to other organic compounds that cannot hydrogen bond.

• Carboxyl group comprises electronegative oxygen double bond to a carbon atom.
• A compound comprising a carboxyl group will possess a high melting point, hydrophilic centres, and boiling point.

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Methods of Preparation of Carboxylic Acids

Some important methods for the preparation of carboxylic acids are as follows:

1. From Primary Alcohols and Aldehydes

Primary alcohols and aldehydes can easily be oxidised to the corresponding carboxylic acids with oxidising agents such as potassium permanganate (in acidic or alkaline medium), potassium dichromate (in acidic medium)

Example

2. Hydrolysis of Nitriles

Nitriles yield carboxylic acids when subjected to hydrolysis with an acid or alkali.

Example

3. Acidic Hydrolysis of Esters

Esters on hydrolysis with dilute mineral acids yield corresponding carboxylic acid

Example

4. From Grignard Reagent

Grignard reagent reacts with carbon dioxide (dry ice) to form salts of carboxylic acid which in turn give corresponding carboxylic acid aftr acidifiation with mineral acid.

Example

Formic acid cannot be prepared by Grignard reagent since the acid contains only one carbon atom.

5. Hydrolysis of Acylhalides and Anhydrides

(a) Acid chlorides when hydrolysed with water give Carboxylic acids.

Example

(b) Acid anhydride when hydrolysed with water give corresponding carboxylic acids.

6. Oxidation of Alkyl Benzenes

Aromatic carboxylic acids can be prepared by vigorous oxidation of alkyl benzene with chromic acid or acidic or alkaline potassium permanganate. The entire side chain is oxidised to – COOH group irrespective of the length of the side chain.

Example

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Structure of Carboxyl Group:

Th carboxyl group represent a planar arrangement of atoms. In – COOH group, the centre carbon atom and both the oxygen atoms are in sp hybridisation. The three sp² hybrid orbitals of the carbon atom overlap.

The two sp² – hybridised orbitals of the carboxyl carbon overlap with one sp² hybridised orbital of each oxygen atom while the third sp² hybridised orbital of carbon overlaps with either a s – orbital of H – atom or a sp² – hybridised orbital of C – atom of the alkyl group to form three s – bonds. Each of the two oxygen atoms and the carbon atom are left with one unhybridised p – orbital which is perpendicular to the s – bonding skeleton.

All these three p – orbitals being parallel overlap to form a π – bond which is partly delocalized between carbon and oxygen atom on one side, and carbon and oxygen of the OH group on the other side. In other words, RCOOH may be represented as a resonance hybrid of the following two canonical structures.

The carboxylic carbon is less electrophilic than carbonyl carbon because of the possible resonance structure. i.e., delocalisation of lone pair electrons from the oxygen in hydroxyl group.

Carboxyl group is a functional organic compound. In this structure of a carboxyl group, a carbon atom is attached to an oxygen atom with the help of a double bond. The carboxyl group ionizes and releases the H atom present in the hydroxyl group part as a free H⁺ ion or a proton.

Carboxylic acid, any of a class of organic compounds in which a carbon (C) atom is bonded to an oxygen (O) atom by a double bond and to a hydroxyl group (- OH) by a single bond. A fourth bond links the carbon atom to a hydrogen (H) atom or to some other univalent combining group.

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.

Carboxyl groups are functional groups with a carbon atom double-bonded to an oxygen atom and single bonded to a hydroxyl group. Ionized carboxyl groups act as acids, require less energy and are more stable. Electron sharing between oxygen atoms on ionized carboxyl groups increases stability.

A carboxyl group (COOH) is a functional group consisting of a carbonyl group (C=O) with a hydroxyl group (O-H) attached to the same carbon atom. Carboxylic acids are a class of molecules which are characterized by the presence of one carboxyl group.

When deprotonated, carboxylate anions are extremely stable due to resonance. This enables carboxyl groups to be influential components of fatty acids and amino acids, which can be further reacted to generate esters, proteins, lipids, and alcohols within the body.

A carboxyl group (COOH) is a functional group consisting of a carbonyl group (C=O) with a hydroxyl group (O-H) attached to the same carbon atom. Carboxyl groups have the formula -C(=O)OH, usually written as -COOH or CO₂H.

Carboxyl groups are commonly found in amino acids, fatty acids, and other biomolecules. An example of a less hydrophilic group is the carbonyl group (C=O), an uncharged but polar (contains partial positive and partial negative charges) functional group.

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Iupac Nomenclature of Carboxylic Acids

The IUPAC name of a carboxylic acid is derived from that of the longest carbon chain that contains the carboxyl group by dropping the final – e from the name of the parent alkane and adding the suffix – oic followed by the word “acid.” The chain is numbered beginning with the carbon of the carboxyl group.

Carboxylic acids are named by counting the number of carbons in the longest continuous chain including the carboxyl group and by replacing the suffix – ane of the corresponding alkane with – anoic acid.

For molecules with two carboxylic acid groups the carbon chain in between the two carboxyl groups (including the carboxyl carbons) is used as the longest chain; the suffix – dioic acid is used. For molecules with more than two carboxylic acid groups, the carboxyl groups are named as carboxylic acid substituents.

Carboxylic acids are the most common type of organic acid. A carboxylic acid is an organic acid that contains a carboxyl group (C(=O)OH) attached to an R-group. The general formula of a carboxylic acid is R-COOH or R-CO₂H, with R referring to the alkyl, alkenyl, aryl, or other group.

Carboxylic acids are commonly identified by their trivial names. They often have the suffix – ic acid. IUPAC-recommended names also exist; in this system, carboxylic acids have an -oic acid suffix. For example, butyric acid (C₃H₇CO₂H) is butanoic acid by IUPAC guidelines.

Carboxylic acids occur in many common household items.

• Vinegar contains acetic acid
• Aspirin is acetylsalicylic acid
• Vitamin C is ascorbic acid
• Lemons contain citric acid, and
• Spinach contains oxalic acid.

Carboxylic acids are weak acids because they only partially ionise in solution. Their solutions do not contain many hydrogen ions compared to a solution of a strong acid at the same concentration.

Carboxylic acids are very important biologically. The drug aspirin is a carboxylic acid, and some people are sensitive to its acidity. Carboxylic acids that have very long chains of carbon atoms attached to them are called fatty acids. As their name suggests, they are important in the formation of fat in the body.

Carboxylic acids are soluble in water. Carboxylic acids do not dimerise in water, but forms hydrogen bonds with water. Carboxylic acids are polar and due to the presence of the hydroxyl in the carboxyl group, they are able to form hydrogen bonds with water molecules.

Aspirin is both an aromatic carboxylic acid (red oval) and a phenyl ester of acetic acid (blue oval). While esterification will convert the carboxylic acid group to a methyl ester, transesterification (exchange of one alcohol portion of an ester for another alcohol) to afford methyl acetate 4 and methyl salicylate 3.

A carboxylic acid is an organic compound that contains a carboxyl group (C(=O)OH) attached to an R-group. The general formula of a carboxylic acid is R-COOH, with R referring to the alkyl group. Important examples include the amino acids and fatty acids.

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Uses of Aldehydes and Ketones

Formaldehyde

1. 40% aqueous solution of formaldehyde is called formalin. It is used for preserving biological specimens.
2. Formalin has hardening effct, hence it is used for tanning.
3. Formalin is used in the production of thermo setting plastic known as bakelite, which is obtained by heating phenol with formalin.

Acetaldehye

1. Acetaldehyde is used for silvering of mirrors
2. Paraldehyde is used in medicine as a hypnotic.
3. Acetaldehyde is used in the commercial preparation of number of organic compounds like acetic acid, ethyl acetate etc.,

Acetone

1. Acetone is used as a solvent, in the manufacture of smokeless gun powder (cordite)
2. It is used as a nail polish remover.
3. It is used in the preparation of sulphonal, a hypnotic.
4. It is used in the manufacture of thermosoftning plastic Perspex.

Benzaldehyde is Used

1. As a flavouring agent
2. In perfumes
3. In dye intermediates
4. As starting material for the synthesis of several other organic compounds like cinnamaldehyde, cinnamic acid, benzoyl chloride etc.

Aromatic Ketones

1. Acetophenone has been used in perfumery and as a hypnotic under the name hypnone.
2. Benzophenone is used in perfumery and in the preparation of benzhydrol eye drop.

Carboxylic Acids

Introduction

Carbon compounds containing a carboxyl function group, -COOH are called carboxylic acids. The Carboxyl group is the combination of carbonyl group and the hydroxyl group (-OH).

However, carboxyl group has its own characteristic reaction. Carboxylic acids may be aliphatic (R – COOH) or aromatic (Ar – COOH) depending on the alkyl or aryl group attached to carboxylic carbon. Some higher members of aliphatic carboxylic acids (C₁₂ to C₁₈) known as fatty acids occur in natural fats as esters of glycerol.

Aldehydes are currently used in the production of resins and plastics. The simplest ketone, propanone, is commonly called acetone. Acetone is a common organic solvent that was one used in most nail polish removers, but has largely been replaced by other solvents.

It is used in tanning, preserving, and embalming and as a germicide, fungicide, and insecticide for plants and vegetables, but its largest application is in the production of certain polymeric materials.

1. Ketone behaves as an excellent solvent for certain types of plastics and synthetic fibres.
2. Acetone act as a paint thinner and a nail paint remover.
3. It also is used for medicinal purposes such as chemical peeling procedure as well as acne treatments.

Example of Ketone

Ketones contain a carbonyl group (a carbon-oxygen double bond). The simplest ketone is acetone (R = R’ = methyl), with the formula CH₃C(O)CH₃. Many ketones are of great importance in biology and in industry. Examples include many sugars (ketoses), many steroids (e.g., testosterone), and the solvent acetone.

Example of Aldehyde

Aldehydes are given the same name but with the suffix – ic acid replaced by – aldehyde. Two examples are formaldehyde and benzaldehyde. As another example, the common name of CH₂ = CHCHO, for which the IUPAC name is 2-propenal, is acrolein, a name derived from that of acrylic acid, the parent carboxylic acid.

Generally, the common names of ketones consist of the names of the groups attached to the carbonyl group, followed by the word ketone. (Note the similarity to the naming of ethers). Another name for acetone, then, is dimethyl ketone. The ketone with four carbon atoms is ethyl methyl ketone.

Common Ketones are Acetone and Methyl Ethyl Ketone. They have different uses. Acetone is known as fingernail polish remover but is also commonly used as lacquer and varnish solvent.

Aldehydes are made by oxidising primary alcohols. The aldehyde produced can be oxidised further to a carboxylic acid by the acidified potassium dichromate (VI) solution used as the oxidising agent. In order to stop at the aldehyde, you have to prevent this from happening.

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Test for Aldehydes

(i) Tollens Reagent Test

Tollens reagent is an ammonical silver nitrate solution. When an aldehyde is warmed with Tollens reagent a bright silver mirror is produced due to the formation of silver metal. This reaction is also called silver mirror test for aldehydes.

(ii) Fehlings Solution Test

Fehlings solution is prepared by mixing equal volumes of Fehlings solution ‘A’ containing aqueous copper sulphate and Fehlings solution ‘B’ containing alkaline solution of sodium potassium tartarate (Rochelle salt)

When aldehyde is warmed with Fehlings solution deep blue colour solution is changed to red precipitate of cuprous oxide.

(iii) Benedict’s Solution Test:

Benedicts solution is a mixture of CuSO₄ + sodium citrate + NaOH.Cu²⁺ is reduced by aldehyde to give red
precipitate of cuprous oxide.

(iv) Schiff’ Reagent Test

Dilute solution of aldehydes when added to schiff’ reagent (Rosaniline hydrochloride dissolved in water and its red colour decolourised by passing SO₂) yields its red colour. This is known as Schiff’ test for aldehydes. Ketones do not give this test. Acetone however gives a positive test but slowly.

An aldehyde is similar to a ketone, except that instead of two side groups connected to the carbonyl carbon, they have at least one hydrogen (RCOH). The simplest aldehyde is formaldehyde (HCOH), as it has two hydrogens connected to the carbonyl group.

Tollen’s reagent is a classical organic laboratory technique to test for the presence of an aldehyde. The reagent consists of silver (I) ions dissolved in dilute ammonia. When the aldehyde is oxidized, the silver (I) ions are reduced to silver metal.

The Schiff test is a chemical test used to check for the presence of aldehydes in a given analyte. This is done by reacting the analyte with a small quantity of a Schiff reagent (which is the product formed in certain dye formulation reactions such as the reaction between sodium bisulfite and fuchsin).

Aldehyde, any of a class of organic compounds in which a carbon atom shares a double bond with an oxygen atom, a single bond with a hydrogen atom, and a single bond with another atom or group of atoms (designated R in general chemical formulas and structure diagrams).

Fehling’s solution can be used to distinguish aldehyde vs ketone functional groups. The compound to be tested is added to the Fehling’s solution and the mixture is heated. Aldehydes are oxidized, giving a positive result, but ketones do not react, unless they are α-hydroxy ketones.

Take the given organic compound in a clean test tube. Add 1ml of chromic acid reagent to the given organic compound. The appearance of a green or blue colour precipitate indicates the presence of aldehydes.