Chapter 14: Compounds with Oxygen, Sulfur, or a Halogen

Compounds with Oxygen, Sulfur, or a Halogen

Alcohols, Phenols, and Ethers

Organic compounds containing oxygen are classified into several families, including alcohols, phenols, and ethers. Their properties and structures are influenced by the nature of the oxygen atom and its bonding.

• Alcohols: Compounds with a hydroxyl (OH) group bonded to a saturated (alkane-like) carbon atom. Example: ethanol (CH3CH2OH).

• Phenols: Compounds with an OH group directly bonded to an aromatic (benzene-like) ring. Example: phenol (C6H5OH).

• Ethers: Compounds with an oxygen atom bonded to two organic groups (alkyl, aromatic, or both). Example: diethyl ether (CH3CH2OCH2CH3).

Alcohols generally have higher boiling and melting points than ethers and hydrocarbons due to hydrogen bonding between molecules and with water.

Naming Alcohols (IUPAC System)

Alcohols are named systematically to reflect their structure and the position of the hydroxyl group.

1. Name the parent compound: Find the longest carbon chain containing the hydroxyl group. Replace the "-e" ending with "-ol" (e.g., hexane → hexanol).

2. Number the chain: Assign the lowest possible number to the carbon bearing the OH group.

3. Write the name: Place the number indicating the position of the OH group before the parent name. Name and number other substituents, listing them alphabetically.

• Cyclic alcohols: Add "-ol" to the parent cycloalkane name and number the ring starting at the OH group.

• Examples: 1-butanol, 5-methyl-3-hexanol, 4-chloro-6-methyl-2-heptanol, cyclopentanol.

Diols and Glycols

Alcohols with two hydroxyl groups are called diols. If the OH groups are on adjacent carbons, the compound is a glycol.

• Examples: Ethylene glycol (1,2-ethanediol), propylene glycol, 1,3-butanediol.

Classification of Alcohols

Alcohols are classified based on the number of carbon atoms attached to the carbon bearing the OH group.

• Primary (1°) alcohol: OH group attached to a carbon bonded to one other carbon.

• Secondary (2°) alcohol: OH group attached to a carbon bonded to two other carbons.

• Tertiary (3°) alcohol: OH group attached to a carbon bonded to three other carbons.

Properties of Alcohols

Small alcohols (e.g., methanol, ethanol) are soluble in water due to hydrogen bonding. Alcohols are both hydrophobic (alkyl chain) and hydrophilic (OH group). Diols have higher boiling points than regular alcohols.

Reactions of Alcohols

Dehydration

Alcohols can lose water to form alkenes. The OH is lost from one carbon, and an H from an adjacent carbon, producing H2O and an alkene.

• Major product: The more substituted alkene (with more alkyl groups attached to the double bond) is favored.

• Example: Dehydration of tert-butyl alcohol yields 2-methylpropene.

Oxidation

Alcohols undergo oxidation to form carbonyl-containing compounds.

• Primary alcohols: Oxidized to aldehydes, then to carboxylic acids.

• Secondary alcohols: Oxidized to ketones.

• Tertiary alcohols: Generally do not undergo oxidation.

Carbonyl group: Functional group with a carbon atom double-bonded to an oxygen atom ($\mathrm{C=O}$).

Oxidation: Increases the number of C–O bonds, decreases C–H bonds. Reduction: Decreases C–O bonds, increases C–H bonds.

Phenols

Phenol is hydroxybenzene (C6H5OH). Phenols are a family of compounds with an OH group on an aromatic ring. They have some water solubility, and alkyl-substituted phenols are less toxic than phenol itself.

• Examples: Ortho-chlorophenol, para-methylphenol.

Acidity of Alcohols and Phenols

Phenols behave as weak acids, dissociating in aqueous solution:

• Example dissociation: $\mathrm{C_6H_5OH \rightarrow C_6H_5O^- + H^+}$

Ethers

Ethers are compounds with an oxygen atom bonded to two organic groups. Simple ethers are named by listing the groups alphabetically followed by "ether" (IUPAC).

• Examples: Dimethyl ether, ethyl methyl ether, diethyl ether.

• Alkoxy group: An OR group used when the ether is a substituent in a compound with other functional groups (e.g., methoxy, ethoxy).

Thiols and Disulfides

Thiols are compounds containing an SH group. Disulfides contain a sulfur-sulfur bond (–S–S–).

• Naming: Add "thiol" to the parent name (e.g., ethanethiol, methylpentanethiol).

• Oxidation: Thiols can be oxidized to disulfides.

Halogen-Containing Compounds

Organic compounds containing halogens are classified as alkyl halides or aryl halides.

• Alkyl halides: Alkyl group bonded to a halogen (R–X, where X = Cl, Br, etc.).

• Aryl halides: Aromatic group bonded to a halogen (Ar–X).

• Naming: Use IUPAC or common names (e.g., chloromethane/methyl chloride).

• Examples: 1-chloropropane, 2-bromo-5-methylhexane.

Stereochemistry

Stereochemistry is the study of the spatial arrangement of atoms in molecules. Stereoisomers have the same molecular and structural formulas but differ in spatial arrangement.

• Configurations: Stereoisomers that cannot be converted into one another by rotation around a single bond.

• Chiral molecules: Have "handedness"; cannot be superimposed on their mirror image. A chiral carbon is tetrahedral and bonded to four different groups.

• Enantiomers: Two mirror-image forms of a chiral molecule; not superimposable.

• Achiral: No handedness; can be superimposed on their mirror image.

Summary Table: Classification and Properties

Compound Type	Functional Group	Example	Key Properties
Alcohol	OH (hydroxyl)	CH3CH2OH (ethanol)	Hydrogen bonding, water solubility, higher boiling point
Phenol	OH on aromatic ring	C6H5OH (phenol)	Weak acid, some water solubility
Ether	O between two groups	CH3CH2OCH2CH3 (diethyl ether)	Lower boiling point, less water solubility
Thiols	SH (sulfhydryl)	CH3CH2SH (ethanethiol)	Distinct odor, can form disulfides
Halides	Cl, Br, etc.	CH3Cl (chloromethane)	Varied reactivity, used in synthesis

Additional info: Academic context was added to clarify naming conventions, reaction mechanisms, and stereochemistry concepts for completeness and exam preparation.