Skip to main content
Back

Alcohols, Aldehydes, and Ketones: Structure, Properties, and Nomenclature

NotesPracticeVideo lessons

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Chapter 12: Alcohols, Aldehydes, and Ketones

12.1 Alcohols, Phenols, Thiols, and Ethers

This section introduces the structure and classification of alcohols, as well as related organic compounds such as phenols, thiols, and ethers.

  • Alcohols are organic compounds containing a hydroxyl group (-OH) attached to a carbon chain. The general formula is R-OH.

  • Carbinol carbon: The carbon atom directly bonded to the hydroxyl group.

  • Alcohols are classified based on the number of hydrogen atoms attached to the carbinol carbon:

Type

Structure

Number of H atoms

Example

Primary (1°)

R-CH2-OH

2

CH3CH2OH (ethanol)

Secondary (2°)

R1-CH(OH)-R2

1

CH3CH(OH)CH3 (2-propanol)

Tertiary (3°)

R1-C(OH)(R2)(R3)

0

(CH3)3COH (tert-butanol)

12.2 Properties of Alcohols

Alcohols exhibit unique physical properties due to the presence of the polar hydroxyl group.

  • Polarity: Alcohols are polar molecules because of the -OH group.

  • Hydrogen bonding: Alcohols can form hydrogen bonds with water, increasing their solubility.

  • Solubility:

    • Alcohols with 1-3 carbons are soluble in water.

    • Alcohols with 4 carbons are slightly soluble in water.

    • Alcohols with 5 or more carbons are insoluble in water due to the nonpolar hydrocarbon chain.

  • Boiling Point: As the molar mass (number of carbons) increases, the boiling point increases due to stronger London dispersion forces.

Example:

Alcohol

Number of Carbons

Boiling Point (relative)

Methanol

1

Lowest

Ethanol

2

Higher

Propanol

3

Higher

Butanol

4

Higher

Hexanol

6

Highest

Solubility Example:

  • CH3CH2OH (ethanol): soluble in water (short chain).

  • CH3CH2CH2CH2CH2OH (pentanol): not soluble in water (long chain).

12.3 Aldehydes and Ketones

Aldehydes and ketones are organic compounds containing a carbonyl group (C=O).

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

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

Compound Type

General Structure

Example

Aldehyde

R-CHO

CH3CH2CHO (propanal)

Ketone

R-CO-R'

CH3COCH3 (2-propanone)

12.3.1 Classification of Organic Compounds

Organic compounds can be classified as alcohols, aldehydes, or ketones based on their functional groups.

  • Alcohol: Contains a hydroxyl (-OH) group.

  • Aldehyde: Contains a carbonyl group at the end of the carbon chain.

  • Ketone: Contains a carbonyl group within the carbon chain.

Example:

Structure

Classification

CH3CH2COCH3

Ketone

CH3CH2CH2CHO

Aldehyde

CH3CH2CH2CH2OH

Alcohol

12.3.2 Nomenclature of Aldehydes

Aldehydes are named by replacing the e in the alkane name with al. The carbonyl carbon is always carbon 1.

  • Methanal: HCHO (formaldehyde)

  • Ethanal: CH3CHO (acetaldehyde)

  • Propanal: CH3CH2CHO

Naming Steps:

  1. Name the longest carbon chain containing the carbonyl group, replacing the e with al.

  2. Name and number substituents by counting the carbonyl group as carbon 1.

Example: CH3CH(CH3)CH2CH2CHO is 2-methylpentanal.

12.3.3 Nomenclature of Ketones

Ketones are named by replacing the e in the alkane name with one. The position of the carbonyl group is indicated by a number.

  • 2-Propanone: CH3COCH3

  • 2-Butanone: CH3COCH2CH3

Naming Steps:

  1. Name the longest carbon chain containing the carbonyl group, replacing the e with one.

  2. Number the chain so the carbonyl group has the lowest possible number.

  3. Name and number any substituents.

Example: CH3COCH(CH3)CH2CH3 is 4-methyl-2-pentanone.

12.4 Practice: Drawing and Naming Compounds

Practice problems involve drawing structures and naming alcohols, aldehydes, and ketones according to IUPAC rules.

  • Draw 3-methyl-2-pentanol:

    • Five-carbon chain (pentane)

    • Methyl group at carbon 3

    • Hydroxyl group at carbon 2

  • Classify alcohols: Determine if primary, secondary, or tertiary based on the number of hydrogens on the carbinol carbon.

  • Arrange alcohols by boiling point: Methanol < Propanol < Butanol < Hexanol < Heptanol

Summary Table: Alcohol Solubility and Boiling Point

Alcohol

Number of Carbons

Water Solubility

Boiling Point

Methanol

1

Soluble

Lowest

Ethanol

2

Soluble

Low

Propanol

3

Soluble

Medium

Butanol

4

Slightly soluble

Higher

Pentanol

5

Insoluble

High

Hexanol

6

Insoluble

Highest

Key Equations and Concepts

  • General formula for alcohols:

  • General formula for aldehydes:

  • General formula for ketones:

  • Boiling point trend: As molar mass increases, boiling point increases.

Additional info:

  • These notes cover foundational organic chemistry concepts relevant to General Chemistry, including structure, classification, physical properties, and nomenclature of alcohols, aldehydes, and ketones.

  • Practice problems and tables are included to reinforce understanding and application of these concepts.

Pearson Logo

Study Prep