Nomenclature And Structure Of Carbonyl Group

This unit focuses on organic compounds containing the **carbonyl functional group** (>C=O). This is a very important functional group in organic chemistry.

• In **aldehydes**, the carbonyl carbon is bonded to at least one hydrogen atom and typically one carbon atom (except for formaldehyde, which has two hydrogen atoms). The general formula is $\textsf{RCHO}$ or $\textsf{ArCHO}$.
• In **ketones**, the carbonyl carbon is bonded to two carbon atoms. The general formula is $\textsf{RCOR'}$ or $\textsf{RCOAr}$ or $\textsf{ArCOAr'}$.

Compounds where the carbonyl carbon is bonded to a carbon or hydrogen and the oxygen of a hydroxyl group (–OH) are called **carboxylic acids** (–COOH). Derivatives of carboxylic acids include amides (–CONH$_2$), acyl halides (–COX), esters (–COOR), and anhydrides (–COOCO–).

Carbonyl compounds like aldehydes, ketones, and carboxylic acids are widespread in nature, contributing to fragrances and flavours (e.g., vanillin, salicylaldehyde, cinnamaldehyde) and playing vital biochemical roles. They are also industrially important as solvents, adhesives, plastics, perfumes, and pharmaceuticals.

Nomenclature

Aldehydes and ketones are named using both common and IUPAC systems.

(a) Common Names:

• Aldehydes: Common names are often derived from the common names of corresponding carboxylic acids by replacing the '-ic acid' ending with '-aldehyde'. The position of substituents on the carbon chain is indicated using Greek letters: $\alpha$ (carbon directly attached to the carbonyl carbon), $\beta$ (next carbon), $\gamma$, $\delta$, etc.
• Ketones: Common names are derived by naming the two alkyl or aryl groups attached to the carbonyl group, followed by the word 'ketone'. Substituent positions are indicated by Greek letters $\alpha, \alpha', \beta, \beta'$ starting from carbons adjacent to the carbonyl group. Simple ketones like dimethyl ketone ($\textsf{CH}_3\text{COCH}_3$) often have historical names (e.g., acetone). Alkyl phenyl ketones are often named by adding the acyl group name as a prefix to 'phenone' (e.g., $\textsf{CH}_3\text{COC}_6\text{H}_5$ is acetophenone).

(b) IUPAC Names:

• Aldehydes: Named from the parent alkane by replacing the ending '-e' with '-al'. The carbonyl carbon is always designated as carbon 1. The longest carbon chain containing the aldehyde group is the parent chain. Substituents are numbered and listed alphabetically. When the aldehyde group is attached to a ring, the suffix 'carbaldehyde' is used after the cycloalkane name; the ring carbon attached to the aldehyde group is C1 of the ring for numbering substituents. Benzaldehyde is the accepted common and IUPAC name for the simplest aromatic aldehyde.
• Ketones: Named from the parent alkane by replacing the ending '-e' with '-one'. The longest carbon chain containing the carbonyl group is the parent chain. Numbering starts from the end nearer to the carbonyl group to give it the lowest possible locant. Substituents are numbered and listed alphabetically. For cyclic ketones, the carbonyl carbon is C1 of the ring.

Examples of aldehyde and ketone nomenclature:

Structure	Common name	IUPAC name
$\textsf{HCHO}$	Formaldehyde	Methanal
$\textsf{CH}_3\text{CHO}$	Acetaldehyde	Ethanal
$\textsf{(CH}_3)_2\text{CHCHO}$	Isobutyraldehyde	2-Methylpropanal
	$\gamma$-Methylcyclohexanecarbaldehyde	3-Methylcyclohexanecarbaldehyde
$\textsf{CH}_3\text{CH(OCH}_3)\text{CHO}$	$\alpha$-Methoxypropionaldehyde	2-Methoxypropanal
$\textsf{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CHO}$	Valeraldehyde	Pentanal
$\textsf{CH}_2\text{=CHCHO}$	Acrolein	Prop-2-enal
	Phthaldehyde	Benzene-1,2-dicarbaldehyde
	m-Bromobenzaldehyde	3-Bromobenzaldehyde
$\textsf{CH}_3\text{CO(CH}_2)_2\text{CH}_3$	Methyl n-propyl ketone	Pentan-2-one
$\textsf{(CH}_3)_2\text{CHCOCH(CH}_3)_2$	Diisopropyl ketone	2,4-Dimethylpentan-3-one
	$\alpha$-Methylcyclohexanone	2-Methylcyclohexanone
$\textsf{(CH}_3)_2\text{C=CHCOCH}_3$	Mesityl oxide	4-Methylpent-3-en-2-one

Structure Of The Carbonyl Group

In the carbonyl group (>C=O), the carbon atom is $\textsf{sp}^2$ hybridised. It forms three sigma ($\sigma$) bonds: one with the oxygen atom and two with other atoms (carbon or hydrogen). The remaining valence electron on carbon is in a p-orbital, which overlaps with a p-orbital on the oxygen atom to form a pi ($\pi$) bond.

The oxygen atom in the carbonyl group also has two non-bonding lone pairs of electrons. The carbonyl carbon and the three atoms bonded to it lie in the same plane, with the $\pi$-electron cloud located above and below this plane. The bond angles around the carbonyl carbon are approximately 120°, consistent with a trigonal planar geometry.

The carbon-oxygen double bond is polar because oxygen is more electronegative than carbon. This gives the carbonyl carbon a partial positive charge (electrophilic centre, acting as a Lewis acid) and the carbonyl oxygen a partial negative charge (nucleophilic centre, acting as a Lewis base).

The polarity of the carbonyl group can be represented by resonance between a neutral structure and a dipolar structure:

This polarity significantly influences the chemical reactivity of aldehydes and ketones.

Preparation Of Aldehydes And Ketones

Several methods are used to synthesise aldehydes and ketones.

Preparation Of Aldehydes And Ketones

These methods can yield both aldehydes and ketones depending on the starting material:

• 1. By Oxidation of Alcohols: Primary alcohols are oxidised to aldehydes, and secondary alcohols are oxidised to ketones. Suitable oxidising agents like PCC (Pyridinium Chlorochromate) are used for primary alcohols to avoid over-oxidation to carboxylic acids. Chromic anhydride ($\textsf{CrO}_3$) or acidified $\textsf{K}_2\text{Cr}_2\text{O}_7$ can oxidise secondary alcohols to ketones.
• 2. By Dehydrogenation of Alcohols: Passing vapours of primary or secondary alcohols over heated copper or silver catalyst at high temperatures (e.g., 573 K) causes dehydrogenation, yielding aldehydes from primary alcohols and ketones from secondary alcohols.
• 3. From Hydrocarbons:
  • (i) By Ozonolysis of Alkenes: Ozonolysis (reaction with ozone, $\textsf{O}_3$) of alkenes followed by reductive workup (e.g., with zinc dust and water) cleaves the carbon-carbon double bond, producing aldehydes and/or ketones. The products depend on the substitution pattern of the original alkene.
  • (ii) By Hydration of Alkynes: Adding water to ethyne (acetylene) in the presence of $\textsf{H}_2\text{SO}_4$ and $\textsf{HgSO}_4$ produces acetaldehyde. Other alkynes, under similar conditions, yield ketones.

Preparation Of Aldehydes

Methods specific to preparing aldehydes:

• 1. From Acyl Chloride (Acid Chloride): Acyl chlorides can be reduced to aldehydes by hydrogenation over a palladium catalyst supported on barium sulfate ($\textsf{Pd-BaSO}_4$). This catalyst is often poisoned with sulfur or quinoline to prevent further reduction of the aldehyde to an alcohol. This reaction is known as **Rosenmund reduction**.
• 2. From Nitriles and Esters:
  • Stephen reaction: Nitriles are reduced to imines using stannous chloride ($\textsf{SnCl}_2$) and $\textsf{HCl}$. Hydrolysis of the imine then yields the corresponding aldehyde.
  • Alternatively, nitriles can be selectively reduced to imines using diisobutylaluminium hydride (DIBAL-H), followed by hydrolysis to give aldehydes.
  • Esters can also be reduced to aldehydes using DIBAL-H at low temperatures.

• 3. From Hydrocarbons (Aromatic Aldehydes): Aromatic aldehydes, particularly benzaldehyde derivatives, are prepared from aromatic hydrocarbons.
  • (i) By Oxidation of Methylbenzene (Toluene): While strong oxidising agents would oxidise toluene to benzoic acid, specific milder conditions can stop the reaction at the aldehyde stage.
    • Etard reaction: Using chromyl chloride ($\textsf{CrO}_2\text{Cl}_2$) which oxidises the methyl group to a chromium complex, which is then hydrolysed to the aldehyde.
    • Using chromic oxide ($\textsf{CrO}_3$): Toluene is converted to benzylidene diacetate using $\textsf{CrO}_3$ in acetic anhydride, which is then hydrolysed with aqueous acid to benzaldehyde.

  • (ii) By Side Chain Chlorination followed by Hydrolysis: Chlorination of the methyl group of toluene under radical conditions yields benzal chloride ($\textsf{C}_6\text{H}_5\text{CHCl}_2$), which upon hydrolysis with water at 373 K yields benzaldehyde. This is a commercial method.
  • (iii) By Gatterman–Koch reaction: Benzene or its derivatives react with carbon monoxide ($\textsf{CO}$) and hydrogen chloride ($\textsf{HCl}$) in the presence of anhydrous aluminium chloride ($\textsf{AlCl}_3$) or cuprous chloride ($\textsf{CuCl}$) as a catalyst to form benzaldehyde or substituted benzaldehydes.

Preparation Of Ketones

Methods specific to preparing ketones:

• 1. From Acyl Chlorides: Acyl chlorides react with dialkylcadmium reagents to produce ketones. Dialkylcadmium is prepared from Grignard reagents and cadmium chloride. This reaction is useful because dialkylcadmium is not reactive enough to react with the resulting ketone.

Preparation of dialkylcadmium: $2\textsf{RMgX} + \textsf{CdCl}_2 \rightarrow \textsf{R}_2\text{Cd} + 2\textsf{MgXCl}$

Reaction with acyl chloride: $\textsf{R'COCl} + \textsf{R}_2\text{Cd} \rightarrow \textsf{R'COR} + \textsf{RCdCl}$

• 2. From Nitriles: Nitriles react with Grignard reagents. Nucleophilic addition of the Grignard reagent to the nitrile's carbon-nitrogen triple bond forms an imine salt, which upon hydrolysis yields a ketone.
• 3. From Benzene or Substituted Benzenes: Aromatic ketones can be prepared by treating benzene or substituted benzenes with acid chlorides or acid anhydrides in the presence of a Lewis acid catalyst, typically anhydrous aluminium chloride ($\textsf{AlCl}_3$). This is the **Friedel-Crafts acylation reaction**.

Answer:

Physical Properties

Physical characteristics of aldehydes and ketones:

• Formaldehyde is a gas at room temperature. Acetaldehyde is a volatile liquid (b.p. 20 °C). Most other simple aldehydes and ketones are liquids, while higher members are solids.
• Boiling Points: Aldehydes and ketones have higher boiling points than hydrocarbons and ethers of similar molecular mass due to weak **dipole-dipole interactions** arising from the polar carbonyl group. However, their boiling points are lower than those of alcohols of similar molecular mass because alcohols can form strong **intermolecular hydrogen bonds**, which are absent in aldehydes and ketones.

Example comparison of boiling points:

• Solubility: Lower molecular mass aldehydes (methanal, ethanal) and ketones (propanone) are miscible with water in all proportions because they can form **hydrogen bonds with water molecules** through the oxygen atom of the carbonyl group.
  Solubility in water decreases rapidly as the length of the non-polar alkyl chain increases. Aldehydes and ketones are generally soluble in common organic solvents like benzene, ether, methanol, and chloroform.
• Odour: Lower aldehydes tend to have sharp, pungent odours. As molecular size increases, the odour becomes less irritating and more fragrant. Many naturally occurring aldehydes and ketones are used in perfumes and flavourings.

Answer:

Chemical Reactions

Aldehydes and ketones share many chemical reactions due to the presence of the carbonyl group.

Nucleophilic Addition Reactions

Aldehydes and ketones characteristic reactions are **nucleophilic addition reactions** across the polarised carbon-oxygen double bond. The nucleophile attacks the electrophilic carbonyl carbon.

(i) Mechanism: A nucleophile ($\textsf{Nu}^-$) attacks the $\textsf{sp}^2$ hybridised carbonyl carbon from a direction perpendicular to the plane of the carbonyl group. This attack changes the hybridisation of the carbon from $\textsf{sp}^2$ to $\textsf{sp}^3$, forming a tetrahedral alkoxide intermediate. This intermediate then quickly accepts a proton ($\textsf{H}^+$) from the reaction medium (or acid catalyst) to give the neutral addition product.

(ii) Reactivity: Aldehydes are generally **more reactive** than ketones towards nucleophilic addition reactions. This difference is due to both steric and electronic factors.

• Steric effects: Aldehydes have one hydrogen atom and one alkyl/aryl group bonded to the carbonyl carbon, while ketones have two alkyl/aryl groups. The presence of two larger substituents in ketones hinders the approach of the nucleophile to the carbonyl carbon compared to aldehydes.
• Electronic effects: Alkyl groups are electron-donating. Aldehydes have only one electron-donating group (except formaldehyde), while ketones have two. The electron-donating effect of alkyl groups increases the electron density on the carbonyl carbon, making it less positive and thus less electrophilic compared to aldehydes.

Answer:

Benzaldehyde ($\textsf{C}_6\text{H}_5\text{CHO}$) has a phenyl group attached to the carbonyl carbon, while propanal ($\textsf{CH}_3\text{CH}_2\text{CHO}$) has an ethyl group.

The phenyl group in benzaldehyde is also attached to the carbonyl carbon. The carbonyl group in benzaldehyde is directly attached to the benzene ring. The $\pi$ electrons of the benzene ring can conjugate with the $\pi$ electrons of the carbonyl group. This resonance interaction reduces the partial positive charge on the carbonyl carbon, making it less electrophilic and less susceptible to nucleophilic attack compared to the carbonyl carbon in propanal, where the ethyl group is electron-donating but does not exhibit resonance with the carbonyl.

Therefore, benzaldehyde is **less reactive** than propanal in nucleophilic addition reactions due to the resonance stabilisation of the carbonyl group by the phenyl ring.

(iii) Important Nucleophilic Addition & Addition-Elimination Reactions:

• (a) Addition of Hydrogen Cyanide (HCN): Aldehydes and ketones react with HCN to form cyanohydrins. The reaction is slow with pure HCN but is catalysed by base, which generates the stronger nucleophile, cyanide ion ($\textsf{CN}^-$). Cyanohydrins are useful intermediates for synthesis.
• (b) Addition of Sodium Hydrogensulphite ($\textsf{NaHSO}_3$): Sodium hydrogensulphite adds to aldehydes and ketones to form crystalline bisulphite addition compounds. The equilibrium position is generally more towards the product for aldehydes than for most ketones due to steric hindrance in ketones. These addition products are water-soluble and can be decomposed back to the original carbonyl compound by treatment with dilute acid or base, making this reaction useful for purification.
• (c) Addition of Grignard Reagents: (As discussed in Chapter 11, Alcohols).
• (d) Addition of Alcohols: Aldehydes react with one equivalent of a monohydric alcohol in the presence of dry $\textsf{HCl}$ gas to form a hemiacetal (an alkoxy alcohol). Hemiacetals further react with another equivalent of alcohol to form an acetal (a geminal dialkoxy compound). Ketones react with ethylene glycol under similar conditions to form cyclic ketals (ethylene glycol ketals). The dry $\textsf{HCl}$ protonates the carbonyl oxygen, enhancing the electrophilicity of the carbonyl carbon. Acetals and ketals can be hydrolysed back to the original carbonyl compounds by aqueous mineral acids.
• (e) Addition of Ammonia and its Derivatives ($\textsf{H}_2\text{N–Z}$): Ammonia and its derivatives (nucleophiles) add to the carbonyl group. This is an acid-catalysed, reversible nucleophilic addition followed by elimination of water to form a carbon-nitrogen double bond ($>\textsf{C=N–Z}$). The elimination step drives the equilibrium towards the product (an imine or its derivative).
  Common derivatives include imines, oximes, hydrazones, phenylhydrazones, 2,4-Dinitrophenylhydrazones (2,4-DNP derivatives), and semicarbazones. 2,4-DNP derivatives are often crystalline solids used for characterisation.

Reduction

• (i) Reduction to Alcohols: Aldehydes are reduced to primary alcohols and ketones to secondary alcohols. This can be achieved by using reducing agents like sodium borohydride ($\textsf{NaBH}_4$) or lithium aluminium hydride ($\textsf{LiAlH}_4$), or by catalytic hydrogenation ($\textsf{H}_2$ with Pt, Pd, or Ni).
• (ii) Reduction to Hydrocarbons: The carbonyl group ($>\textsf{C=O}$) can be completely reduced to a methylene group ($>\textsf{CH}_2$), converting aldehydes/ketones into the corresponding alkanes.
  • **Clemmensen reduction:** Treatment with zinc-amalgam ($\textsf{Zn-Hg}$) and concentrated hydrochloric acid ($\textsf{HCl}$).
  • **Wolff-Kishner reduction:** Treatment with hydrazine ($\textsf{NH}_2\text{NH}_2$) followed by heating with sodium or potassium hydroxide in a high-boiling solvent like ethylene glycol.

Oxidation

Oxidation reactions are used to distinguish aldehydes from ketones.

• Aldehydes are easily oxidised to carboxylic acids by various oxidising agents, including common ones like nitric acid, $\textsf{KMnO}_4$, $\textsf{K}_2\text{Cr}_2\text{O}_7$, and even mild ones like Tollens' and Fehling's reagents.
• Ketones are generally resistant to oxidation under normal conditions and require strong oxidising agents and elevated temperatures. Their oxidation involves breaking carbon-carbon bonds adjacent to the carbonyl, leading to a mixture of carboxylic acids with fewer carbon atoms.

Mild oxidising agents used for differentiation:

• (i) Tollens’ Test: Aldehydes are warmed with Tollens’ reagent (freshly prepared ammoniacal silver nitrate solution). A 'silver mirror' is formed on the inside of the reaction vessel due to the reduction of $\textsf{Ag}^+$ ions to silver metal. The aldehyde is oxidised to the carboxylate anion in the alkaline medium. Ketones do not give this test.
• (ii) Fehling’s Test: Aldehydes are heated with Fehling’s reagent (a mixture of Fehling solution A - aqueous $\textsf{CuSO}_4$, and Fehling solution B - alkaline sodium potassium tartarate). A reddish-brown precipitate of cuprous oxide ($\textsf{Cu}_2\text{O}$) is formed as $\textsf{Cu}^{2+}$ ions are reduced to $\textsf{Cu}^+$ ions. The aldehyde is oxidised to the carboxylate anion. Aromatic aldehydes typically do not respond to this test. Ketones do not give this test.
• (iii) Oxidation of Methyl Ketones by Haloform Reaction: Aldehydes and ketones containing the acetyl group ($\textsf{CH}_3\text{CO–}$) are oxidised by sodium hypohalite ($\textsf{NaOX}$, generated from $\textsf{NaOH}$ and $\textsf{X}_2$). This reaction cleaves the carbon-carbon bond next to the carbonyl, producing a sodium salt of a carboxylic acid with one less carbon atom and a haloform ($\textsf{CHX}_3$). The iodoform test (using $\textsf{NaOI}$ from $\textsf{NaOH}$ and $\textsf{I}_2$) gives a characteristic yellow precipitate of iodoform ($\textsf{CHI}_3$) and is used to detect the presence of the $\textsf{CH}_3\text{CO–}$ group or a $\textsf{CH}_3\text{CH(OH)–}$ group (which is oxidised to $\textsf{CH}_3\text{CO–}$ under the reaction conditions). This oxidation does not affect carbon-carbon double bonds.

Answer:

Compound (A) ($\textsf{C}_8\text{H}_8\text{O}$) forms a 2,4-DNP precipitate, indicating it contains a carbonyl group (aldehyde or ketone).

It does not reduce Tollens' or Fehling's reagent, ruling out aldehyde functionality (except possibly aromatic aldehydes for Fehling's, but further tests clarify). Thus, (A) is likely a **ketone**.

(A) gives a yellow precipitate with $\textsf{I}_2$/$\textsf{NaOH}$ (positive iodoform test), meaning it is a methyl ketone ($\textsf{CH}_3\text{CO–}$ group).

The molecular formula $\textsf{C}_8\text{H}_8\text{O}$ suggests high unsaturation (Degree of Unsaturation = $8 - 8/2 + 1 = 5$). It doesn't decolourise bromine water or Baeyer's reagent, indicating the unsaturation is likely due to an aromatic ring, not C=C or C$\equiv$C bonds.

Compound (B) ($\textsf{C}_7\text{H}_6\text{O}_2$) is a carboxylic acid produced by oxidation of ketone (A). Benzoic acid has the formula $\textsf{C}_7\text{H}_6\text{O}_2$. If (B) is benzoic acid, then (A) must be a methyl ketone attached to a phenyl ring.

With a molecular formula of $\textsf{C}_8\text{H}_8\text{O}$, the only possible aromatic methyl ketone is phenyl methyl ketone, also known as **acetophenone** ($\textsf{C}_6\text{H}_5\text{COCH}_3$).

Let's check if acetophenone fits all the given properties:

• Molecular formula: $\textsf{C}_6\text{H}_5\text{COCH}_3 = \textsf{C}_8\text{H}_8\text{O}$ (Matches).
• 2,4-DNP derivative: Yes, ketones form 2,4-DNP derivatives.
• Yellow precipitate with $\textsf{I}_2$/$\textsf{NaOH}$: Yes, acetophenone is a methyl ketone.
• Reduces Tollens'/'Fehling's: No, it's a ketone.
• Decolourises bromine water/Baeyer's: No, the unsaturation is in the stable aromatic ring.
• Oxidation to carboxylic acid ($\textsf{C}_7\text{H}_6\text{O}_2$): Vigorous oxidation of acetophenone with chromic acid cleaves the C-C bond adjacent to the carbonyl (between the carbonyl carbon and the phenyl ring), oxidising the phenyl group to benzoic acid ($\textsf{C}_6\text{H}_5\text{COOH}$, $\textsf{C}_7\text{H}_6\text{O}_2$).

All properties match. Therefore, Compound (A) is Acetophenone, and Compound (B) is Benzoic acid.

Reactions involved:

Iodoform test on (A): $\textsf{C}_6\text{H}_5\text{COCH}_3 + 3\textsf{NaOI} \rightarrow \textsf{C}_6\text{H}_5\text{COONa} + \textsf{CHI}_3 (\text{yellow ppt}) + 2\textsf{NaOH}$

Oxidation of (A) to (B): $\textsf{C}_6\text{H}_5\text{COCH}_3 \xrightarrow{\textsf{Chromic acid}} \textsf{C}_6\text{H}_5\text{COOH}$

Reactions Due To $\alpha$-hydrogen

The hydrogen atoms on the carbon atom adjacent to the carbonyl group ($\alpha$-carbon) are called $\alpha$-hydrogens. These hydrogens are acidic due to the electron-withdrawing nature of the carbonyl group and the resonance stabilisation of the carbanion (enolate ion) formed after the removal of an $\alpha$-hydrogen.

This acidity leads to characteristic reactions:

• (i) Aldol Condensation: Aldehydes and ketones with at least one $\alpha$-hydrogen undergo a reaction in the presence of dilute alkali (base catalyst) to form $\beta$-hydroxy aldehydes (aldols) or $\beta$-hydroxy ketones (ketols). This reaction is called the **Aldol reaction**. The term "aldol" comes from aldehyde + alcohol. Ketones also undergo this reaction, yielding ketols (ketone + alcohol).
  Aldols and ketols are often unstable and readily lose a water molecule upon heating or treatment with acid/base to form $\alpha$,$\beta$-unsaturated carbonyl compounds. This subsequent elimination step is called **Aldol condensation**.
• (ii) Cross Aldol Condensation: Aldol condensation carried out between two different carbonyl compounds (both having $\alpha$-hydrogens) is called cross aldol condensation. This typically leads to a mixture of four products (two self-condensation products and two cross-condensation products), which can be difficult to separate.
  Cross aldol reactions are more useful when one reactant has no $\alpha$-hydrogens (e.g., benzaldehyde or formaldehyde) and acts only as the electrophile, while the other has $\alpha$-hydrogens and acts as the nucleophile (enolate donor).

Other Reactions

• (i) Cannizzaro Reaction: Aldehydes that **do not have any $\alpha$-hydrogen** atoms (e.g., formaldehyde, benzaldehyde, pivalaldehyde) undergo a disproportionation reaction when heated with concentrated alkali. One molecule is reduced to the corresponding alcohol, and another is oxidised to the carboxylic acid salt.
• (ii) Electrophilic Substitution Reaction (Aromatic Aldehydes and Ketones): Aromatic aldehydes and ketones undergo electrophilic substitution on the benzene ring. The carbonyl group ($>\textsf{C=O}$) is an electron-withdrawing group. When directly attached to the benzene ring, it is a **deactivating** and **meta-directing** group for electrophilic substitution reactions.

Uses Of Aldehydes And Ketones

Aldehydes and ketones are widely used in various industries:

• They serve as important **solvents** (e.g., acetone, ethyl methyl ketone).
• They are used as **starting materials** and **reagents** in organic synthesis to build more complex molecules.
• **Formaldehyde** (40% solution is formalin) is used for preserving biological specimens and in the production of polymers like Bakelite (phenol-formaldehyde resin) and urea-formaldehyde glues.
• **Acetaldehyde** is a precursor for manufacturing acetic acid, ethyl acetate, vinyl acetate, polymers, and pharmaceuticals.
• **Benzaldehyde** is used in the flavour, perfumery, and dye industries.
• Many aldehydes and ketones are valued for their pleasant **odours and flavours** and are used in perfumes and flavouring agents (e.g., butyraldehyde, vanillin, acetophenone, camphor).

Carboxylic Acids

Carboxylic acids are organic compounds containing the **carboxyl functional group** (–COOH). This group is a combination of a carbonyl ($>\textsf{C=O}$) and a hydroxyl (–OH) group.

Carboxylic acids can be aliphatic ($\textsf{RCOOH}$) or aromatic ($\textsf{ArCOOH}$). Higher aliphatic carboxylic acids with 12 to 18 carbon atoms are known as **fatty acids** and occur naturally as esters in fats and oils.

Carboxylic acids are essential starting materials for synthesising many other functional groups and compounds like anhydrides, esters, acid chlorides, and amides.

Nomenclature

Carboxylic acids are named using both common and IUPAC systems.

• Common Names: Many simple carboxylic acids have common names derived from their natural sources, ending with '-ic acid'. Examples: formic acid (from ants, *formica*), acetic acid (from vinegar, *acetum*), butyric acid (from butter, *butyrum*).
• IUPAC Names: Aliphatic carboxylic acids are named by replacing the final '-e' of the corresponding alkane name with '-oic acid'. The carbon atom of the carboxyl group is always numbered as 1. For dicarboxylic acids, the suffix is '-dioic acid', retaining the '-e' of the alkane. For compounds with more than two carboxyl groups, the carbon chain is numbered excluding the carboxyl carbons, and '-carboxylic acid' is added with numerical prefixes and locants. The simplest aromatic carboxylic acid is benzoic acid ($\textsf{C}_6\text{H}_5\text{COOH}$), which is also the accepted IUPAC name (or benzenecarboxylic acid).

Examples of carboxylic acid nomenclature:

Structure	Common name	IUPAC name
$\textsf{HCOOH}$	Formic acid	Methanoic acid
$\textsf{CH}_3\text{COOH}$	Acetic acid	Ethanoic acid
$\textsf{CH}_3\text{CH}_2\text{COOH}$	Propionic acid	Propanoic acid
$\textsf{CH}_3\text{CH}_2\text{CH}_2\text{COOH}$	Butyric acid	Butanoic acid
$\textsf{(CH}_3)_2\text{CHCOOH}$	Isobutyric acid	2-Methylpropanoic acid
$\textsf{HOOC-COOH}$	Oxalic acid	Ethanedioic acid
$\textsf{HOOC -CH}_2\text{-COOH}$	Malonic acid	Propanedioic acid
$\textsf{HOOC -(CH}_2)_2\text{-COOH}$	Succinic acid	Butanedioic acid
$\textsf{HOOC -(CH}_2)_3\text{-COOH}$	Glutaric acid	Pentanedioic acid
$\textsf{HOOC -(CH}_2)_4\text{-COOH}$	Adipic acid	Hexanedioic acid
$\textsf{HOOC -CH}_2\text{-CH(COOH)-CH}_2\text{-COOH}$	Tricarballylic acid or carballylic acid	Propane-1,2,3-tricarboxylic acid
$\textsf{C}_6\text{H}_5\text{COOH}$	Benzoic acid	Benzoic acid (Benzenecarboxylic acid)
$\textsf{C}_6\text{H}_5\text{CH}_2\text{COOH}$	Phenylacetic acid	2-Phenylethanoic acid
	Phthalic acid	Benzene-1,2-dicarboxylic acid

Structure Of Carboxyl Group

In the carboxyl group (–COOH), the carbon atom is $\textsf{sp}^2$ hybridised. The bonds to the carboxyl carbon lie in a plane, separated by approximately 120° angles.

The carboxyl group exhibits resonance due to the interaction between the lone pair on the hydroxyl oxygen and the $\pi$ system of the carbonyl group:

These resonance structures show that the carboxyl carbon is less electrophilic compared to the carbonyl carbon in aldehydes and ketones because the positive charge character is delocalised away from the carbon onto the hydroxyl oxygen.

Methods Of Preparation Of Carboxylic Acids

Various methods are available for synthesising carboxylic acids.

From Primary Alcohols And Aldehydes

Primary alcohols can be oxidised to carboxylic acids using strong oxidising agents like potassium permanganate ($\textsf{KMnO}_4$) (in neutral, acidic, or alkaline conditions), potassium dichromate ($\textsf{K}_2\text{Cr}_2\text{O}_7$) in acidic medium, or chromium trioxide ($\textsf{CrO}_3$) in acidic medium (Jones reagent).

$\textsf{RCH}_2\text{OH} \xrightarrow{\textsf{KMnO}_4 \text{ or } \textsf{K}_2\text{Cr}_2\text{O}_7/\textsf{H}^+ \text{ or Jones reagent}} \textsf{RCOOH}$

Aldehydes are readily oxidised to carboxylic acids even by milder oxidising agents like Tollens' or Fehling's reagents (as discussed in the Aldehydes and Ketones section).

From Alkylbenzenes

Aromatic carboxylic acids can be prepared by the vigorous oxidation of alkyl benzenes. Strong oxidising agents like chromic acid or acidic/alkaline potassium permanganate oxidise the entire alkyl side chain attached to the benzene ring to a carboxyl group, regardless of the chain length (provided it has at least one benzylic hydrogen). Tertiary alkyl groups are not oxidised by this method.

From Nitriles And Amides

Nitriles ($\textsf{RCN}$) can be hydrolysed in the presence of acid ($\textsf{H}^+$) or base ($\textsf{OH}^-$) catalysts. Acid hydrolysis first yields an amide, which is then further hydrolysed to a carboxylic acid. Basic hydrolysis yields the carboxylate salt, which needs acidification to get the carboxylic acid. Mild conditions can stop the reaction at the amide stage.

Acid hydrolysis: $\textsf{R–C}\equiv\textsf{N} \xrightarrow{\textsf{H}^+/\textsf{H}_2\text{O}} \textsf{RCONH}_2 \xrightarrow{\textsf{H}^+/\textsf{H}_2\text{O}} \textsf{RCOOH}$

Basic hydrolysis: $\textsf{R–C}\equiv\textsf{N} \xrightarrow{\textsf{OH}^-/\textsf{H}_2\text{O}} \textsf{RCOO}^- \xrightarrow{\textsf{H}^+} \textsf{RCOOH}$

From Grignard Reagents

Grignard reagents ($\textsf{RMgX}$) react with solid carbon dioxide (dry ice) to form magnesium carboxylate salts. Subsequent acidification with a mineral acid liberates the carboxylic acid.

Since Grignard reagents can be prepared from alkyl halides, this method (along with hydrolysis of nitriles) is useful for converting an alkyl halide into a carboxylic acid with one additional carbon atom (ascending the carbon series).

From Acyl Halides And Anhydrides

Acyl halides ($\textsf{RCOCl}$) undergo hydrolysis to give carboxylic acids. This reaction is faster in the presence of aqueous base, yielding the carboxylate ion which is then acidified.

$\textsf{RCOCl} + \textsf{H}_2\text{O} \rightarrow \textsf{RCOOH} + \textsf{HCl}$

$\textsf{RCOCl} + \textsf{NaOH} \rightarrow \textsf{RCOONa} + \textsf{HCl}$ then $\textsf{RCOONa} \xrightarrow{\textsf{H}^+} \textsf{RCOOH}$

Acid anhydrides also hydrolyse with water to give the corresponding carboxylic acid(s).

$\textsf{(RCO)}_2\text{O} + \textsf{H}_2\text{O} \rightarrow 2\textsf{RCOOH}$

From Esters

Esters ($\textsf{RCOOR'}$) can be hydrolysed to carboxylic acids. Acidic hydrolysis (using acid catalyst) directly yields the carboxylic acid and alcohol. Basic hydrolysis (saponification) yields the carboxylate salt and alcohol; subsequent acidification of the salt provides the carboxylic acid.

Acidic hydrolysis: $\textsf{RCOOR'} \xrightarrow{\textsf{H}^+/\textsf{H}_2\text{O}} \textsf{RCOOH} + \textsf{R'OH}$

Basic hydrolysis: $\textsf{RCOOR'} \xrightarrow{\textsf{OH}^-/\textsf{H}_2\text{O}} \textsf{RCOO}^- + \textsf{R'OH}$ then $\textsf{RCOO}^- \xrightarrow{\textsf{H}^+} \textsf{RCOOH}$

Answer:

(i) Oxidation of primary alcohol to carboxylic acid. Reagent: Strong oxidising agent like alkaline $\textsf{KMnO}_4$ followed by acidification.

$\textsf{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{OH} \xrightarrow{\textsf{Alkaline KMnO}_4, \text{ heat}} \textsf{CH}_3\text{CH}_2\text{CH}_2\text{COO}^- \xrightarrow{\textsf{H}^+} \textsf{CH}_3\text{CH}_2\text{CH}_2\text{COOH}$

(ii) Convert benzyl alcohol ($\textsf{C}_6\text{H}_5\text{CH}_2\text{OH}$) to phenylethanoic acid ($\textsf{C}_6\text{H}_5\text{CH}_2\text{COOH}$). This requires adding one carbon atom. Convert alcohol to alkyl halide, then to nitrile, then hydrolyse. Or convert alcohol to aldehyde, react with Grignard reagent (adds carbon), then oxidise (this would add 2 carbons if aldehyde from benzyl alcohol reacts with CH3MgX). Simpler route: alcohol to alkyl halide, then nitrile, then hydrolysis.

$\textsf{C}_6\text{H}_5\text{CH}_2\text{OH} \xrightarrow{\textsf{SOCl}_2} \textsf{C}_6\text{H}_5\text{CH}_2\text{Cl} \xrightarrow{\textsf{KCN}} \textsf{C}_6\text{H}_5\text{CH}_2\text{CN} \xrightarrow{\textsf{H}^+/\textsf{H}_2\text{O}} \textsf{C}_6\text{H}_5\text{CH}_2\text{COOH}$

(iii) Convert 3-nitrobromobenzene to 3-nitrobenzoic acid. This involves replacing bromine with a carboxyl group, which usually requires adding a carbon. Convert aryl halide to Grignard reagent, then react with $\textsf{CO}_2$, then acidify.

(iv) Convert 4-methylacetophenone to benzene-1,4-dicarboxylic acid (terephthalic acid). This requires oxidising both the methyl group and the acetyl methyl group to carboxyl groups. Vigorous oxidation conditions are needed, e.g., alkaline $\textsf{KMnO}_4$ followed by acidification.

(v) Convert cyclohexene to hexane-1,6-dioic acid (adipic acid). This requires oxidative cleavage of the double bond and oxidation of the terminal carbons to carboxylic acids. Strong oxidising agents like alkaline $\textsf{KMnO}_4$ or acidified $\textsf{K}_2\text{Cr}_2\text{O}_7$ are suitable for cleaving the double bond and oxidising fragments to carboxylic acids.

(vi) Convert butanal to butanoic acid. This is oxidation of an aldehyde to a carboxylic acid, which can be done with common oxidising agents like $\textsf{KMnO}_4$ or $\textsf{K}_2\text{Cr}_2\text{O}_7/\textsf{H}^+$. Even mild agents work, but usually strong ones are mentioned for complete oxidation to acid.

$\textsf{CH}_3\text{CH}_2\text{CH}_2\text{CHO} \xrightarrow{\textsf{KMnO}_4/\textsf{OH}^- \text{ or } \textsf{K}_2\text{Cr}_2\text{O}_7/\textsf{H}^+} \textsf{CH}_3\text{CH}_2\text{CH}_2\text{COOH}$

Physical Properties

Physical characteristics of carboxylic acids:

• Lower aliphatic carboxylic acids (up to 9 carbons) are colourless liquids with pungent odours. Higher acids are odourless, wax-like solids due to low volatility.
• Boiling Points: Carboxylic acids have significantly higher boiling points than aldehydes, ketones, and even alcohols of comparable molecular masses. This is because they form strong **intermolecular hydrogen bonds**, leading to extensive association of molecules. In fact, they often exist as stable cyclic **dimers** in the vapour phase or in aprotic solvents due to hydrogen bonding between two molecules.
• Solubility: Simple aliphatic carboxylic acids (up to 4 carbon atoms) are miscible with water because they can form **hydrogen bonds with water** molecules.
  Solubility decreases as the hydrocarbon chain length increases due to the growing hydrophobic character. Higher carboxylic acids are practically insoluble in water. Benzoic acid, the simplest aromatic acid, is sparingly soluble in cold water but dissolves in less polar organic solvents like benzene, ether, alcohol, and chloroform.

Chemical Reactions

Carboxylic acids undergo reactions involving the cleavage of O–H bonds (due to acidity), C–OH bonds (nucleophilic substitution at acyl carbon), and reactions of the entire carboxyl group or the hydrocarbon part.

Reactions Involving Cleavage Of O–H Bond

The O–H bond in carboxylic acids is polar, allowing proton donation (acidity).

• Acidity: Carboxylic acids dissociate in water to form carboxylate ions and hydronium ions. The acidity is quantified by the acid dissociation constant ($K_\text{a}$) or its negative logarithm, $\textsf{p}K_\text{a}$ ( $\textsf{p}K_\text{a} = -\textsf{log} K_\text{a}$). A lower $\textsf{p}K_\text{a}$ means a stronger acid.

$K_\text{a} = \frac{\textsf{[RCOO}^-]\textsf{[H}_3\text{O}^+]}{\textsf{[RCOOH]}}$

• Carboxylic acids are stronger acids than alcohols ($\textsf{p}K_\text{a} \approx 16$) and most simple phenols ($\textsf{p}K_\text{a} \approx 10$). This is because the carboxylate anion ($\textsf{RCOO}^-$) formed after deprotonation is highly stabilised by resonance, with the negative charge delocalised equally over two electronegative oxygen atoms in equivalent resonance structures.
• In contrast, the phenoxide ion ($\textsf{C}_6\text{H}_5\text{O}^-$) is stabilised by resonance, but the negative charge is delocalised onto less electronegative carbon atoms in non-equivalent structures. This makes carboxylate ions more stable than phenoxide ions, resulting in carboxylic acids being stronger acids than phenols.
• Effect of Substituents on Acidity:
  • **Electron-withdrawing groups (EWG)** near the carboxyl group increase acidity by stabilising the carboxylate anion through inductive and/or resonance effects, spreading out the negative charge. The effect is stronger when the EWG is closer to the carboxyl group and when the group is more electronegative or there are more EWGs. Example increasing acidity: $\textsf{CH}_3\text{COOH} < \textsf{FCH}_2\text{COOH} < \textsf{ClCH}_2\text{COOH} < \textsf{BrCH}_2\text{COOH} < \textsf{ICH}_2\text{COOH}$. Halogens' effect: $\textsf{I < Br < Cl < F}$. Number of halogens: $\textsf{CH}_3\text{COOH} < \textsf{ClCH}_2\text{COOH} < \textsf{CHCl}_2\text{COOH} < \textsf{CCl}_3\text{COOH}$.
  • **Electron-donating groups (EDG)** decrease acidity by destabilising the carboxylate anion, concentrating the negative charge on the oxygen atoms. Alkyl groups are weakly electron-donating, so increasing alkyl chain length slightly decreases acidity.
• Direct attachment of groups with $\textsf{sp}^2$ or $\textsf{sp}$ hybridised carbons (like phenyl or vinyl groups) increases acidity compared to saturated alkyl groups. This is mainly due to the higher electronegativity of $\textsf{sp}^2$ carbons compared to $\textsf{sp}^3$ carbons, allowing them to withdraw electron density inductively, although resonance effects can also play a role. For aromatic acids, EWGs on the ring increase acidity, while EDGs decrease it.
• Reactions with Metals and Alkalies: Carboxylic acids react with active metals (like Na) to produce hydrogen and a carboxylate salt. They also react with strong bases (like NaOH) to form salts. Crucially, unlike phenols, carboxylic acids are acidic enough to react with weaker bases like carbonates ($\textsf{Na}_2\text{CO}_3$) and bicarbonates ($\textsf{NaHCO}_3$), releasing carbon dioxide gas. This $\textsf{CO}_2$ evolution is a simple test for the presence of a carboxyl group.

$\textsf{RCOOH} + \textsf{Na} \rightarrow \textsf{RCOONa} + 1/2 \textsf{H}_2$

$\textsf{RCOOH} + \textsf{NaOH} \rightarrow \textsf{RCOONa} + \textsf{H}_2\text{O}$

$\textsf{RCOOH} + \textsf{NaHCO}_3 \rightarrow \textsf{RCOONa} + \textsf{H}_2\text{O} + \textsf{CO}_2$

Example 12.8. Which acid of each pair shown here would you expect to be stronger?

(i) $\textsf{CH}_3\text{CO}_2\text{H}$ or $\textsf{CH}_2\text{FCO}_2\text{H}$

(ii) $\textsf{CH}_2\text{FCO}_2\text{H}$ or $\textsf{CH}_2\text{ClCO}_2\text{H}$

(iii) $\textsf{CH}_2\text{FCH}_2\text{CH}_2\text{CO}_2\text{H}$ or $\textsf{CH}_3\text{CHFCH}_2\text{CO}_2\text{H}$

(iv)

Answer:

Acidity is increased by electron-withdrawing groups (EWG) and decreased by electron-donating groups (EDG). The effect of inductive withdrawal decreases with distance from the carboxyl group. Electronegativity order: F > Cl.

(i) $\textsf{CH}_3\text{COOH}$ vs $\textsf{CH}_2\text{FCOOH}$. Fluorine is an EWG, methyl is weakly EDG. Fluorine stabilises the carboxylate anion more than methyl. Therefore, $\textsf{CH}_2\text{FCO}_2\text{H}$ is stronger.

Stronger acid: $\textsf{CH}_2\text{FCO}_2\text{H}$.

(ii) $\textsf{CH}_2\text{FCO}_2\text{H}$ vs $\textsf{CH}_2\text{ClCO}_2\text{H}$. Both F and Cl are EWGs. Fluorine is more electronegative than chlorine, so it withdraws electrons more strongly, better stabilising the carboxylate anion. Therefore, fluoroacetic acid is stronger than chloroacetic acid.

Stronger acid: $\textsf{CH}_2\text{FCO}_2\text{H}$.

(iii) $\textsf{CH}_2\text{FCH}_2\text{CH}_2\text{CO}_2\text{H}$ vs $\textsf{CH}_3\text{CHFCH}_2\text{CO}_2\text{H}$. Both have a fluorine atom EWG. In the first compound, F is on the $\gamma$-carbon (three carbons away from COOH). In the second compound, F is on the $\beta$-carbon (two carbons away from COOH). The inductive effect of an EWG decreases rapidly with distance. Therefore, the fluorine on the $\beta$-carbon has a stronger acid-strengthening effect than the fluorine on the $\gamma$-carbon.

Stronger acid: $\textsf{CH}_3\text{CHFCH}_2\text{CO}_2\text{H}$.

(iv)

The first compound is benzoic acid. The second is 4-nitrobenzoic acid. The nitro group ($\textsf{NO}_2$) is a strong EWG, both by induction and resonance. Located at the *para* position, it significantly stabilises the carboxylate anion of benzoic acid. Benzoic acid itself is more acidic than aliphatic acids due to the inductive withdrawal by the $\textsf{sp}^2$ carbons of the ring and resonance stabilisation of the carboxylate into the ring (minor). Adding a strong EWG like $\textsf{NO}_2$ makes it much stronger.

Stronger acid: 4-Nitrobenzoic acid.

Reactions Involving Cleavage Of C–OH Bond

These reactions involve nucleophilic substitution at the acyl carbon, where the hydroxyl group is replaced by a nucleophile. Carboxylic acids react as a source of acyl groups ($\textsf{RCO–}$).

• 1. Formation of Anhydride: Carboxylic acids lose a water molecule upon heating with strong dehydrating agents like concentrated $\textsf{H}_2\text{SO}_4$ or $\textsf{P}_2\text{O}_5$, forming carboxylic acid anhydrides.
• 2. Esterification: Carboxylic acids react with alcohols or phenols in the presence of an acid catalyst (like concentrated $\textsf{H}_2\text{SO}_4$ or dry $\textsf{HCl}$ gas) to form esters. This is a reversible reaction.
  The mechanism is a nucleophilic acyl substitution initiated by protonation of the carbonyl oxygen, making the carbonyl carbon more electrophilic for attack by the alcohol nucleophile. Subsequent proton transfers and elimination of water lead to the ester.
• 3. Reactions with $\textsf{PCl}_5$, $\textsf{PCl}_3$, and $\textsf{SOCl}_2$: The –OH group of carboxylic acids can be replaced by a chlorine atom using phosphorus pentachloride ($\textsf{PCl}_5$), phosphorus trichloride ($\textsf{PCl}_3$), or thionyl chloride ($\textsf{SOCl}_2$). This yields acyl chlorides. Thionyl chloride is often preferred as the other products ($\textsf{SO}_2$ and $\textsf{HCl}$) are gases and easily escape, simplifying product purification.
• 4. Reaction with Ammonia: Carboxylic acids react with ammonia ($\textsf{NH}_3$) to form ammonium carboxylate salts. Heating these salts strongly yields amides ($\textsf{RCONH}_2$).

Reactions Involving –COOH Group

These reactions involve the transformation of the entire carboxyl group.

• 1. Reduction: Carboxylic acids can be reduced to primary alcohols ($\textsf{RCH}_2\text{OH}$). Strong reducing agents like lithium aluminium hydride ($\textsf{LiAlH}_4$) are effective. Diborane ($\textsf{B}_2\text{H}_6$) in ether is also a good reducing agent for carboxylic acids and tolerates other functional groups that $\textsf{LiAlH}_4$ might reduce (like esters, nitro, halides). Sodium borohydride ($\textsf{NaBH}_4$) does not reduce the carboxyl group.
• 2. Decarboxylation: Carboxylic acids can lose a molecule of carbon dioxide (decarboxylation), typically when their sodium salts are heated with soda lime (a mixture of $\textsf{NaOH}$ and $\textsf{CaO}$ in a 3:1 ratio). This forms a hydrocarbon with one less carbon atom than the original acid.
  Electrolysis of aqueous solutions of alkali metal salts of carboxylic acids also causes decarboxylation and coupling of alkyl radicals to form hydrocarbons (Kolbe electrolysis).

Substitution Reactions In The Hydrocarbon Part

• 1. Halogenation (Hell-Volhard-Zelinsky reaction): Aliphatic carboxylic acids having at least one $\alpha$-hydrogen atom can be halogenated at the $\alpha$-position. Treatment with chlorine ($\textsf{Cl}_2$) or bromine ($\textsf{Br}_2$) in the presence of a small amount of red phosphorus yields $\alpha$-halocarboxylic acids. This reaction is known as the **Hell-Volhard-Zelinsky (HVZ) reaction**.
• 2. Ring Substitution (Aromatic Carboxylic Acids): Aromatic carboxylic acids undergo electrophilic substitution reactions on the benzene ring. The carboxyl group (–COOH) is an electron-withdrawing group when directly attached to the ring. Thus, it is a **deactivating** and **meta-directing** group for electrophilic substitution. They do not undergo Friedel-Crafts reactions because the carboxyl group deactivates the ring and also complexes with the $\textsf{AlCl}_3$ catalyst.

Uses Of Carboxylic Acids

Carboxylic acids have numerous applications:

• **Methanoic acid (Formic acid):** Used in the rubber, textile, dyeing, leather, and electroplating industries.
• **Ethanoic acid (Acetic acid):** Used as a solvent and in the food industry as vinegar (typically 5% solution).
• **Hexanedioic acid (Adipic acid):** Used in the manufacture of nylon-6,6, a type of polyamide.
• **Esters of benzoic acid:** Used in perfumery due to their pleasant fragrances.
• **Sodium benzoate:** Used as a food preservative.
• Higher fatty acids ($\textsf{C}_{12}-\textsf{C}_{18}$): Used in the manufacture of soaps and detergents.

Answer:

Question 12.2. Write the structures of products of the following reactions;

(i)

(ii) $(C_6H_5CH_2)_2Cd + 2CH_3COCl \rightarrow$

(iii)

(iv)

Answer:

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Question 12.5. Predict the products of the following reactions:

(i)

(ii)

(iii)

(iv)

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Question 12.8. Which acid of each pair shown here would you expect to be stronger?

(i) $CH_3CO_2H$ or $CH_2FCO_2H$

(ii) $CH_2FCO_2H$ or $CH_2ClCO_2H$

(iii) $CH_2FCH_2CH_2CO_2H$ or $CH_3CHFCH_2CO_2H$

(iv)

Answer:

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Question 12.4. Write the IUPAC names of the following ketones and aldehydes. Wherever possible, give also common names.

(i) $CH_3CO(CH_2)_4CH_3$

(ii) $CH_3CH_2CHBrCH_2CH(CH_3)CHO$

(iii) $CH_3(CH_2)_5CHO$

(iv) $Ph-CH=CH-CHO$

(v)

(vi) $PhCOPh$

Answer:

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Question 12.17. Complete each synthesis by giving missing starting material, reagent or products

(i)

(ii)

(iii)

(iv)

(v)

(vi)

(vii)

(viii)

(ix)

(x)

(xi)

Answer:

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