Hydrocarbons: Structure, Properties, and Reactions (Chapter 11 Study Notes)

Hydrocarbons and Organic Chemistry

Introduction to Organic Chemistry

Organic chemistry is the study of compounds containing carbon, typically bonded with hydrogen and sometimes other elements. Organic compounds are distinguished from inorganic compounds by their structure, bonding, and properties.

• Organic compound: Contains carbon and hydrogen.

• Inorganic compound: Does not contain both carbon and hydrogen.

• Organic chemistry: The study of organic compounds.

Comparison of Organic and Inorganic Compounds

Organic and inorganic compounds differ in their bonding, physical properties, and chemical behavior.

Property	Organic Compounds	Inorganic Compounds
Elements Present	C, H, sometimes O, S, N, Cl, Br, I	Most metals and nonmetals
Bonding	Mostly covalent	Many are ionic, some covalent
Polarity	Nonpolar, unless a strongly electronegative atom is present	Most are ionic or polar covalent
Melting/Boiling Point	Usually low	Usually high
Solubility	High in nonpolar solvents	High in water
Flammability	Burns in air	Most are nonflammable

Additional info: Organic compounds are often nonpolar, have low melting and boiling points, weak intermolecular forces, are less water soluble, have low density, and are flammable.

Hydrocarbons: Structure and Classification

Definition and Types of Hydrocarbons

Hydrocarbons are organic compounds composed exclusively of carbon and hydrogen atoms. They are classified based on the types of bonds and structures present.

• Hydrocarbon: Contains only carbon and hydrogen.

• Alkane: Hydrocarbon with only single bonds between carbon atoms.

• Alkene: Hydrocarbon with one or more double bonds.

• Alkyne: Hydrocarbon with one or more triple bonds.

Bonding and Shapes of Carbon Compounds

Carbon atoms form four covalent bonds and do not possess lone pairs in organic molecules. The geometry around carbon depends on the type of bonds:

• Tetrahedral: All single bonds (alkanes).

• Trigonal planar: Contains a double bond (alkenes).

• Linear: Contains a triple bond (alkynes).

Structural Isomerism

Structural isomers are compounds with the same molecular formula but different connectivity of atoms.

• Structural isomer: Same chemical formula, different atom arrangement.

Naming Alkanes

Alkanes are named according to the IUPAC system, which involves identifying the longest carbon chain and naming substituents.

1. Determine the longest continuous chain (parent chain) and use the suffix -ane.

2. Number the parent chain to give the lowest possible numbers to substituents.

3. Name substituents as "#-name" in alphabetical order.

• Linear alkane: No branches.

• Branched alkane: Not all carbons are in a row.

• Parent chain: Longest continuous chain of carbon atoms.

• Substituent: Atom/group not part of the parent chain.

• Alkyl group: Substituent containing only carbon and hydrogen.

Common Alkanes and Their Formulas

The first ten alkanes are named according to the number of carbon atoms.

Name	Molecular Formula	Condensed Structural Formula
Methane	CH4	CH4
Ethane	C2H6	CH3-CH3
Propane	C3H8	CH3-CH2-CH3
Butane	C4H10	CH3-CH2-CH2-CH3
Pentane	C5H12	CH3-CH2-CH2-CH2-CH3
Hexane	C6H14	CH3-CH2-CH2-CH2-CH2-CH3
Heptane	C7H16	CH3-...-CH3
Octane	C8H18	CH3-...-CH3
Nonane	C9H20	CH3-...-CH3
Decane	C10H22	CH3-...-CH3

Additional info: The general formula for alkanes is $C_nH_{2n+2}$.

Properties of Alkanes

Physical Properties and Uses

Alkanes exhibit a range of physical properties depending on their molecular size. Their uses are determined by their state at room temperature.

• 1-4 carbons: Gas at room temperature (fuels).

• 5-8 carbons: Liquid at room temperature (gasoline).

• 9-17 carbons: High boiling point liquids (kerosine, diesel, jet fuel, motor oil, mineral oil).

• 18+ carbons: Solid at room temperature (waxes, ointments, cosmetics, lubricants).

• Alkanes are the least reactive family of organic compounds.

Combustion reaction:

$C_xH_y + O_2 \rightarrow CO_2 + H_2O$

Saturated and Unsaturated Hydrocarbons

Definitions and Classification

Hydrocarbons are classified as saturated or unsaturated based on the presence of multiple bonds or rings.

• Saturated hydrocarbon: Contains the maximum number of hydrogen atoms; only single bonds, no rings.

• Unsaturated hydrocarbon: Contains fewer than the maximum number of hydrogens due to double bonds, triple bonds, or rings.

• Alkene: Contains one or more double bonds.

• Alkyne: Contains one or more triple bonds.

Note: There is no free rotation around double bonds.

Addition Reactions

Addition reactions involve the addition of atoms across multiple bonds in unsaturated hydrocarbons.

• Hydrogenation: Addition of hydrogen.

• Halogenation: Addition of halogens.

• Hydration: Addition of water.

Markovnikov's Rule: In the addition of H-X to an alkene, the hydrogen atom attaches to the carbon with more hydrogen atoms already present.

Polymers and Monomers

Polymer Chemistry

Polymers are large molecules made up of repeating units called monomers. Many everyday materials are polymers derived from hydrocarbons.

• Polymer: Large molecule consisting of small repeating units.

• Monomer: The repeating unit in a polymer.

• Millions of tons of plastics are produced annually.

Common Polymers and Their Uses

Polymer Section	Common Use
Polyethylene (—CH2—CH2—)	Plastic bottles, insulation
Polypropylene (—CH2—CH(CH3)—)	Plastic pipes, garden hoses, garbage bins
Polystyrene (—CH2—CH(Ph)—)	Packaging, insulation
Polytetrafluoroethylene (Teflon, —CF2—CF2—)	Nonstick coatings, plastic implants
Polyvinyl chloride (—CH2—CHCl—)	Insulation, pipes, cartons

Additional info: Polymers are synthesized by addition or condensation reactions, and their properties depend on the monomers used.