Alkanes, Cycloalkanes, and Halogenated Alkanes

Identification and Nomenclature

• Alkanes are saturated hydrocarbons with the general formula .

• Cycloalkanes are ring-shaped saturated hydrocarbons with the formula .

• Halogenated alkanes (alkyl halides) are alkanes where one or more hydrogens are replaced by halogen atoms (F, Cl, Br, I).

• Identification can be by name (IUPAC or common), molecular or structural formula, or 3D/line-angle/expanded structure.

Saturated vs. Unsaturated Hydrocarbons

• Saturated hydrocarbons: Only single bonds (alkanes, cycloalkanes).

• Unsaturated hydrocarbons: Contain double or triple bonds (alkenes, alkynes) or aromatic rings.

Classification of Carbon Atoms and Alkyl Halides

• Primary (1°): Carbon attached to one other carbon.

• Secondary (2°): Carbon attached to two other carbons.

• Tertiary (3°): Carbon attached to three other carbons.

• Quaternary (4°): Carbon attached to four other carbons.

• Alkyl halides are classified by the type of carbon to which the halogen is attached.

3D Shape and Bonding in Hydrocarbons

• Carbon atoms in alkanes are tetrahedral ( hybridized), with bond angles of approximately .

• Bonding involves sigma () bonds between carbon and hydrogen or other carbons.

Physical Properties of Alkanes

• Boiling point: Increases with molecular weight and surface area; branched alkanes have lower boiling points than straight-chain isomers.

• Solubility: Insoluble in water; soluble in nonpolar solvents.

• Density: Less dense than water (typically 0.6–0.8 g/mL).

Isomerism in Alkanes and Cycloalkanes

• Constitutional (structural) isomers: Same molecular formula, different connectivity.

• Cis/trans cyclic diastereomers: Stereoisomers in cycloalkanes with two substituents; differ in spatial arrangement (cis = same side, trans = opposite sides).

Reactions of Alkanes

• Halogenation: Substitution of H by halogen (e.g., chlorination, bromination).

• Combustion: Complete combustion produces and . Equation:

Chirality and Stereochemistry

Chiral Centers and Stereoisomers

• A chiral center is a tetrahedral carbon bonded to four different groups.

• Enantiomers: Non-superimposable mirror images.

• Diastereomers: Stereoisomers that are not mirror images.

Optical Activity and Polarimetry

• Chiral molecules rotate plane-polarized light; this property is measured using a polarimeter.

• The direction and degree of rotation are characteristic of the enantiomer and its concentration.

Alkenes, Alkynes, and Aromatic Hydrocarbons

Nomenclature and Identification

• Use IUPAC rules to name alkenes (double bonds), alkynes (triple bonds), cycloalkenes, and aromatic hydrocarbons (e.g., benzene derivatives).

Stereoisomerism in Alkenes

• Alkenes can exhibit cis/trans (E/Z) isomerism when each carbon of the double bond has two different substituents.

Physical Properties of Unsaturated Molecules

• Generally, alkenes and alkynes have lower boiling points than corresponding alkanes due to less efficient packing.

• Aromatic compounds have unique stability and properties due to delocalized electrons.

Reactions of Alkenes and Aromatics

• Combustion: Similar to alkanes, producing and .

• (De)hydrogenation: Addition or removal of across double/triple bonds.

• Halogenation: Addition of (e.g., Br, Cl$_2$) across double bonds.

• Hydrohalogenation: Addition of HX (e.g., HBr, HCl).

• Hydration: Addition of to form alcohols.

• Alkylation/Halogenation of Aromatics: Electrophilic aromatic substitution reactions.

Alkene-Derived Molecules

• Terpenes: Built from isoprene units; found in essential oils.

• Pheromones: Chemical signals in organisms, often derived from alkenes.

• Addition polymers: Formed by polymerization of alkenes (e.g., polyethylene).

Alcohols, Phenols, Thiols, Ethers, and Thioethers

Nomenclature and Classification

• Use IUPAC rules to name alcohols, phenols, thiols, ethers, and thioethers.

• Alcohols are classified as primary, secondary, or tertiary based on the carbon to which the OH group is attached.

Physical Properties

• Alcohols and phenols have higher boiling points due to hydrogen bonding.

• Ethers and thioethers have lower boiling points and are less soluble in water.

• Thiols have distinctive odors and lower boiling points than alcohols.

Reactions

• Combustion: Complete oxidation to and .

• Dehydration: Loss of water to form alkenes.

• Halogenation: Replacement of H by halogen.

• Condensation: Formation of ethers from alcohols (Williamson synthesis).

• Oxidation: Mild oxidants convert primary alcohols to aldehydes, secondary to ketones.

Isomerism

• Isomerism arises from different positions of the functional group or different carbon skeletons.

Aldehydes, Ketones, Carboxylic Acids, and Derivatives

Nomenclature

• Use IUPAC rules to name aldehydes, ketones, carboxylic acids, esters, acyl chlorides, and acid anhydrides.

• Multiple principal groups are named according to priority rules.

Physical Properties

• Carbonyl compounds have higher boiling points than alkanes but lower than alcohols.

• Carboxylic acids have high boiling points due to hydrogen bonding and dimer formation.

Reactions

• Formation from alcohols: Oxidation of primary alcohols yields aldehydes; secondary yields ketones.

• Oxidation of aldehydes: Produces carboxylic acids.

• Reduction of carbonyls: Converts aldehydes/ketones to alcohols.

• (Hemi)acetal formation: Reaction of aldehydes/ketones with alcohols.

• Esterification: Carboxylic acid + alcohol forms ester and water.

• Decarboxylation: Loss of from carboxylic acids.

• Hydrolysis and saponification: Breakdown of esters in water or base.

Isomerism

• Isomerism includes position and functional group isomers, especially with unsaturated oxygen functionalities.

Amines and Amides

Nomenclature and Classification

• Use IUPAC rules to name amines and amides, including when multiple principal groups are present.

Physical Properties

• Amines have moderate boiling points; primary and secondary amines can hydrogen bond.

• Amides have higher boiling points due to strong hydrogen bonding.

Reactions

• Alkylation: Introduction of alkyl groups to amines.

• Protonation (acid-base chemistry): Amines act as bases and accept protons.

• Amidification: Formation of amides from carboxylic acids and amines.

• Hydrolysis: Amides can be hydrolyzed to carboxylic acids and amines.

Carbohydrates

Identification and Classification

• General formula: .

• Aldoses: Monosaccharides with an aldehyde group.

• Ketoses: Monosaccharides with a ketone group.

• Classified by number of carbons: triose (3), tetrose (4), pentose (5), hexose (6).

Structural Representations

• Fischer projections: 2D representations showing stereochemistry at each carbon.

• Haworth projections: Cyclic forms of monosaccharides.

• Conversion between Fischer and Haworth projections is essential for understanding carbohydrate chemistry.

Stereochemistry of Sugars

• Enantiomers: Mirror-image isomers (e.g., D- and L-glucose).

• Diastereomers: Stereoisomers that are not mirror images.

Glycosidic Linkages

• Disaccharides are formed by glycosidic bonds between monosaccharides.

• Identification of linkage position (e.g., 1→4, 1→6) is important for structure and function.

Summary Table: Functional Groups and Key Properties

Additional info: This guide synthesizes the key learning objectives and foundational concepts from the provided syllabus, expanding on each topic with definitions, examples, and academic context for effective exam preparation.