CH 14+16 STUDY NOTES

Chapter 14 – Aldehydes and Ketones

Continuing Organic Chemistry

Organic chemistry involves the study of carbon-containing compounds, including their structures, reactions, and nomenclature. After covering aromatics, alcohols, thiols, ethers, alkanes, alkenes, and alkynes, we now focus on carbonyl-containing compounds.

• Carbonyl group (C=O): A functional group consisting of a carbon atom double-bonded to an oxygen atom. It is present in several important classes of organic compounds, including aldehydes, ketones, carboxylic acids, esters, amides, and acyl halides.

• Examples: Aldehyde, ketone, carboxylic acid, ester, amide, acyl halide.

Simplest Carbonyls: Aldehydes and Ketones

Aldehydes and ketones are the simplest carbonyl-containing compounds.

• Aldehyde: The carbonyl carbon is attached to at least one hydrogen atom. General formula: R-CHO.

• Ketone: The carbonyl carbon is attached to two other carbon atoms. General formula: R-CO-R'.

• Example: Acetaldehyde (CH3CHO) is an aldehyde; acetone (CH3COCH3) is a ketone.

Naming Aldehydes

Aldehydes are named by replacing the "-e" ending of the parent alkane with "-al." For this course, numbering is not required since the aldehyde group is always at the end of the chain.

• Examples:

  • Methanal (formaldehyde): HCHO

  • Ethanal (acetaldehyde): CH3CHO

  • Propanal: CH3CH2CHO

  • Butanal: CH3CH2CH2CHO

Aromatic Aldehydes

Benzaldehydes are aromatic compounds with an aldehyde group attached directly to the benzene ring. The carbon bearing the aldehyde is always numbered as carbon 1.

• Example: Benzaldehyde (C6H5CHO)

Naming Ketones

Ketones are named by replacing the "-e" ending of the parent alkane with "-one." The position of the carbonyl group is indicated by a number if necessary.

• Examples:

  • Propanone (acetone): CH3COCH3

  • Butanone: CH3COCH2CH3

  • 3-Pentanone: CH3CH2COCH2CH3

  • Cyclopentanone: cyclic structure with a ketone group

  • 3-Methylcyclohexanone: methyl group at position 3 on cyclohexanone

Physical Properties: Dipole Interactions

Both aldehydes and ketones have strong dipole-dipole interactions due to the polar carbonyl group. This affects their boiling points and solubility.

• Boiling points: Higher than alkanes but lower than alcohols of similar molar mass.

• Example Table:

Name	Molar Mass	Family	Boiling Point (°C)
Butane	58	Alkane	0
Propanal	58	Aldehyde	49
Propanone	58	Ketone	56
1-Propanol	60	Alcohol	97

Reactions of Aldehydes and Ketones

Oxidation

• Aldehydes can be oxidized to carboxylic acids.

• Ketones generally cannot be oxidized further under mild conditions because they lack a hydrogen atom on the carbonyl carbon.

• Equation:

$\ce{CH3CH2CHO} \xrightarrow{[O]} \ce{CH3CH2COOH}$

(Propanal to propanoic acid)

Tollens' Test

• Used to distinguish aldehydes from ketones.

• Aldehydes reduce Ag+ to metallic silver, forming a "silver mirror." Ketones do not react.

• Equation:

$\ce{RCHO + 2Ag^+ + 2OH^- \rightarrow RCOO^- + 2Ag(s) + H2O}$

Benedict's Test

• Also distinguishes aldehydes from ketones.

• Aldehydes reduce Cu2+ to Cu2O (red precipitate); ketones do not react.

• Useful for identifying reducing sugars.

Reduction

• Aldehydes and ketones can be reduced to alcohols.

• Aldehydes produce primary alcohols; ketones produce secondary alcohols.

• Equation:

$\ce{RCHO + H2 \rightarrow RCH2OH}$

$\ce{RCOR' + H2 \rightarrow RCH(OH)R'}$

Acetals and Hemiacetals

• Alcohols add to aldehydes and ketones to form hemiacetals (one alcohol added) and acetals (two alcohols added).

• These reactions are acid-catalyzed.

• Example:

$\ce{RCHO + R'OH \xrightarrow{H^+} RCH(OH)OR'}$ (hemiacetal)

$\ce{RCH(OH)OR' + R'OH \xrightarrow{H^+} RCH(OR')2 + H2O}$ (acetal)

Cyclic Hemiacetals

• Cyclic hemiacetals form when a molecule contains both a carbonyl and a hydroxyl group, allowing intramolecular reaction.

• Important in carbohydrate chemistry (e.g., glucose forms a cyclic hemiacetal).

Chapter 16 – Carboxylic Acids and Esters

Carboxylic Acids

Carboxylic acids are weak acids found in many biological and food contexts (e.g., acetic acid in vinegar, propanoic acid in rotting fruit). They contain a carbonyl group attached to a hydroxyl group (–COOH).

• General formula: R–COOH

• Example: Acetic acid (CH3COOH), propanoic acid (CH3CH2COOH)

Naming Carboxylic Acids

Carboxylic acids are named by replacing the "-e" ending of the parent alkane with "-oic acid."

• Examples:

  • Methanoic acid (formic acid): HCOOH

  • Ethanoic acid (acetic acid): CH3COOH

  • Propanoic acid: CH3CH2COOH

  • Benzoic acid: C6H5COOH

Condensed Structural Formula	Line Angle Formula	IUPAC Name
HCOOH		Methanoic acid
CH3COOH		Ethanoic acid
CH3CH2COOH		Propanoic acid
CH3CH2CH2COOH		Butanoic acid

Formation of Carboxylic Acids

Carboxylic acids can be formed by the oxidation of primary alcohols and aldehydes.

• Equation:

$\ce{CH3CH2OH \xrightarrow{[O]} CH3CHO \xrightarrow{[O]} CH3COOH}$

(Ethanol to ethanal to ethanoic acid)

Properties of Carboxylic Acids

• Contain two polar groups: carbonyl (C=O) and hydroxyl (–OH).

• Form strong hydrogen bonds, leading to higher boiling points than aldehydes, ketones, and alcohols of similar molar mass.

• Are weak acids, partially ionizing in water to form carboxylate ions and hydronium ions.

• Equation:

$\ce{RCOOH + H2O \rightleftharpoons RCOO^- + H3O^+}$

IUPAC Name	Condensed Structural Formula	Boiling Point (°C)	Solubility in Water	Acid Dissociation Constant (Ka)
Ethanoic acid	CH3COOH	118	Soluble	1.8 × 10−5
Benzoic acid	C6H5COOH	249	Slightly soluble	6.3 × 10−5

Carboxylate Salts

Carboxylic acids react with bases to form carboxylate salts, which are often used as food preservatives and flavor enhancers.

• Equation:

$\ce{RCOOH + NaOH \rightarrow RCOO^- Na^+ + H2O}$

Esters

Esters are derived from carboxylic acids, with the hydroxyl group replaced by an alkoxy (–OR) group. They are commonly found in fragrances and flavors.

• General formula: R–COOR'

• Example: Methyl ethanoate (CH3COOCH3)

Esterification

Esters are formed by the reaction of carboxylic acids with alcohols in the presence of an acid catalyst (Fischer esterification).

• Equation:

$\ce{RCOOH + R'OH \xrightarrow{H^+,\ heat} RCOOR' + H2O}$

Naming Esters

The name of an ester is derived from the alcohol and acid used to make it. The alkyl group from the alcohol is named first, followed by the acid part with the ending "-oate."

• Example: Ethanoic acid + methanol → methyl ethanoate

Properties of Esters

• Esters have two polar groups but cannot hydrogen bond with themselves, resulting in lower boiling points than carboxylic acids and alcohols.

• Example Table:

Name	Molar Mass	Family	Boiling Point (°C)
Butane	58	Alkane	0
Methyl methanoate	60	Ester	32
1-Propanol	60	Alcohol	97
Ethanoic acid	60	Carboxylic acid	118

Hydrolysis of Esters

Acid Hydrolysis

• Esters react with water and acid to yield carboxylic acids and alcohols (reverse of esterification).

• Equation:

$\ce{RCOOR' + H2O \xrightarrow{H^+,\ heat} RCOOH + R'OH}$

Base Hydrolysis (Saponification)

• Esters react with a base (e.g., NaOH) to form a carboxylate salt and an alcohol. This is the process used in soap making.

• Equation:

$\ce{RCOOR' + NaOH \rightarrow RCOO^- Na^+ + R'OH}$

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