Alcohols, Phenols, Ethers, and Thiols: Structure, Nomenclature, Properties, and Reactions

Alcohols, Phenols, Ethers, and Thiols

Overview and Learning Objectives

This section introduces the structure, nomenclature, classification, physical properties, and chemical reactions of alcohols, phenols, ethers, and thiols. These functional groups are fundamental in organic and biological chemistry, with wide-ranging applications in health, industry, and daily life.

• Identify IUPAC and common names, and structural formulas for alcohols, phenols, ethers, and thiols.

• Classify alcohols as primary, secondary, or tertiary and relate their physical and chemical properties to structure.

• Represent the formation of alcohols via hydration of alkenes and the reverse dehydration reaction.

• Describe the formation of ethers through condensation of alcohols.

• List common applications of alcohols, ethers, and thiols.

Alcohols

Structure and Definition

Alcohols are organic molecules in which one or more hydrogen atoms of an alkane have been replaced by a hydroxyl group (-OH).

• The -OH group attached to a carbon chain is called a hydroxyl.

• General formula: R-OH, where R is an alkyl group.

• Examples: Methanol (CH3OH), Ethanol (CH3CH2OH).

Naming Alcohols

Alcohols are named using the IUPAC system or common names.

• IUPAC: Name the parent hydrocarbon, replace the final '-e' with '-ol', and number the carbon to which the -OH is attached.

• Common names: Use the alkyl group name followed by 'alcohol' (e.g., methyl alcohol).

• Aromatic alcohols are named as phenol.

Formula	IUPAC Name	Common Name
CH3OH	methanol	methyl alcohol
CH3CH2OH	ethanol	ethyl alcohol
CH3CH(OH)CH3	2-propanol	isopropyl alcohol

IUPAC Rules for Naming Alcohols

1. Name the longest chain containing the -OH group.

2. Number the chain to give the lowest number to the carbon with the -OH.

3. Indicate the position of the -OH by the number of the carbon atom.

Example: CH3-CH2-CH(OH)-CH2-CH2-CH3 is 3-hexanol.

Naming Alcohols with Other Groups

• Identify and name other substituents attached to the main chain.

• Combine the names and locations of substituents, the -OH position, and the main chain.

• Alcohols with two -OH groups are called diols; with three, triols (e.g., hexane-3,4-diol).

Naming Phenols

• Substituted phenols are named as derivatives of phenol.

• Number the ring to give the lowest possible numbers to substituents, starting with the carbon holding the -OH as 1.

• If identical numbers are possible, assign the lowest number to the group that comes first alphabetically.

Examples: 2-chloro-6-methylphenol, 3-chloro-5-methylphenol.

Formation of Alcohols

Hydration of Alkenes

Alcohols can be synthesized by the hydration of alkenes:

• An alkene reacts with water (H-OH) in the presence of a strong acid catalyst (e.g., H2SO4).

• The hydrogen atom from water adds to the carbon with more hydrogen atoms (Markovnikov's rule).

• The -OH group adds to the other carbon of the double bond.

General equation:

$ext{Alkene} + ext{H}_2 ext{O} ightarrow ext{Alcohol}$

Example:

$ext{CH}_3 ext{CH}= ext{CH}_2 + ext{H}_2 ext{O} ightarrow ext{CH}_3 ext{CH}_2 ext{CH}_2 ext{OH}$

Uses of Alcohols and Phenols

• Alcohols: Used in beverages, antiseptics, hand sanitizers, solvents, and preservatives.

• Phenols: Used as antiseptics, in plastics, dyes, and hospital disinfectants.

Classification of Alcohols

Primary, Secondary, and Tertiary Alcohols

Alcohols are classified by the number of alkyl groups attached to the carbon bonded to the hydroxyl group:

• Primary (1°) alcohol: One alkyl group attached (e.g., ethanol).

• Secondary (2°) alcohol: Two alkyl groups attached (e.g., 2-propanol).

• Tertiary (3°) alcohol: Three alkyl groups attached (e.g., 2-methyl-2-propanol).

Physical Properties of Alcohols

Solubility in Water

Alcohols contain polar -OH groups and can form hydrogen bonds with water and other alcohol molecules.

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

• Solubility decreases as the number of carbons increases.

Compound	Condensed Formula	Number of Carbons	Solubility in Water
Methanol	CH3OH	1	Soluble
Ethanol	CH3CH2OH	2	Soluble
1-Propanol	CH3CH2CH2OH	3	Soluble
1-Butanol	CH3CH2CH2CH2OH	4	Slightly soluble
1-Pentanol	CH3CH2CH2CH2CH2OH	5	Insoluble

Boiling Points

• The -OH group enables hydrogen bonding, resulting in higher boiling points than alkanes and ethers of similar molecular weight.

• Boiling point increases with molecular weight and number of -OH groups.

Chemical Reactions of Alcohols

Combustion

Alcohols combust in oxygen to produce carbon dioxide, water, and energy.

$ext{Alcohol} + ext{O}_2(g) ightarrow ext{CO}_2(g) + ext{H}_2 ext{O}(g) + ext{energy}$

Example:

$ext{CH}_3 ext{CH}_2 ext{OH} + 3 ext{O}_2 ightarrow 2 ext{CO}_2 + 3 ext{H}_2 ext{O} + ext{energy}$

Dehydration

• Intramolecular dehydration (at 180°C): Alcohol loses H and OH from adjacent carbons to form an alkene and water.

• Intermolecular dehydration (at 140°C): Two alcohol molecules lose H and OH to form an ether and water (condensation reaction).

General equation for ether formation:

$ext{R-OH} + ext{R'-OH} ightarrow ext{R-O-R'} + ext{H}_2 ext{O}$

Oxidation and Reduction

• Oxidation: Increases the number of carbon-oxygen bonds (addition of oxygen or loss of hydrogen).

• Reduction: Decreases the number of carbon-oxygen bonds (addition of hydrogen or loss of oxygen).

Oxidation	Reduction
Loss of hydrogen Addition of oxygen	Addition of hydrogen Loss of oxygen

Oxidation of Alcohols

• Primary (1°) alcohols: Oxidized to aldehydes, which can further oxidize to carboxylic acids.

• Secondary (2°) alcohols: Oxidized to ketones.

• Tertiary (3°) alcohols: Do not oxidize under normal conditions (no hydrogen on the carbon with -OH).

Example equations:

Primary alcohol oxidation:

$ext{R-CH}_2 ext{OH} ightarrow[ ext{O}] ext{R-CHO} ightarrow[ ext{O}] ext{R-COOH}$

Secondary alcohol oxidation:

$ext{R}_2 ext{CH-OH} ightarrow[ ext{O}] ext{R}_2 ext{C=O}$

Biological Significance

• Alcohols are metabolized in the liver via oxidation to aldehydes and carboxylic acids.

• Lactic acid in muscles is oxidized to pyruvic acid during exercise, which is further converted to CO2 and H2O.

Study Checks and Practice Problems

• Name alcohols using IUPAC nomenclature.

• Classify alcohols as primary, secondary, or tertiary.

• Predict products of hydration and dehydration reactions.

• Determine solubility and boiling points based on structure.

• Draw oxidation products for given alcohols.

Additional info:

• These notes cover content relevant to General Chemistry, specifically organic functional groups, their nomenclature, properties, and reactions.

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