Chapter 12: Introduction to Organic Chemistry – Hydrocarbons

Introduction to Organic Chemistry: Hydrocarbons

Overview

Organic chemistry is the branch of chemistry that studies carbon-containing compounds, especially those containing carbon and hydrogen. Hydrocarbons are the simplest class of organic compounds and serve as the foundation for understanding more complex organic molecules.

• Organic compounds are primarily composed of carbon and hydrogen, and may also contain oxygen, nitrogen, sulfur, phosphorus, or halogens (F, Cl, Br, I).

• Organic chemistry is essential for understanding substances found in living organisms, medicines, plastics, and many everyday materials.

Organic vs. Inorganic Compounds

Key Differences

Organic and inorganic compounds differ in composition, bonding, properties, and solubility. The following table summarizes these differences:

Property	Organic Compounds	Inorganic Compounds
Elements Present	C and H, sometimes O, S, N, P, or halogens	Most metals and nonmetals
Type of Particles	Molecules	Mostly ions
Bonding	Mostly covalent	Many are ionic, some covalent
Polarity	Nonpolar unless a strongly electronegative atom is present	Most are ionic or polar covalent, a few are nonpolar covalent
Melting/Boiling Point	Usually low	Usually high
Flammability	High (burns in air)	Low
Solubility in Water	Not soluble unless a polar group is present	Most are soluble unless nonpolar

Classification and Properties of Hydrocarbons

Types of Hydrocarbons

Hydrocarbons are organic compounds consisting only of carbon and hydrogen. They are classified based on the types of bonds between carbon atoms:

• Alkanes: Contain only single bonds (saturated hydrocarbons).

• Alkenes: Contain at least one double bond (unsaturated hydrocarbons).

• Alkynes: Contain at least one triple bond (unsaturated hydrocarbons).

• Aromatic hydrocarbons: Contain benzene rings with delocalized electrons.

General Properties

• Hydrocarbons tend to be nonpolar and have low melting and boiling points.

• They are usually insoluble in water but soluble in nonpolar solvents.

• Most are flammable and burn in air to produce carbon dioxide and water.

Representations of Organic Molecules

Structural Formulas

Organic molecules can be represented in several ways to convey their structure:

• Expanded structural formulas: Show all atoms and bonds explicitly.

• Condensed structural formulas: Group atoms together to simplify the structure.

• Line-angle formulas: Use lines to represent carbon-carbon bonds; carbon and hydrogen atoms are often implied.

Naming Organic Compounds: The IUPAC System

Systematic Naming

The International Union of Pure and Applied Chemistry (IUPAC) system provides rules for naming organic compounds based on their structure:

• Identify the longest continuous carbon chain (parent chain).

• Number the chain from the end nearest a substituent or functional group.

• Name and number substituents (branches or functional groups) as prefixes.

• For alkanes, use the suffix -ane; for alkenes, -ene; for alkynes, -yne.

Summary Diagram: Hydrocarbon Classification and Reactions

The following flowchart summarizes the classification and key reactions of hydrocarbons:

• Organic compounds → Hydrocarbons → Alkanes, Alkenes, Alkynes

• Alkanes: Single bonds, undergo combustion

• Alkenes: Double bonds, can form cis-trans isomers, undergo addition reactions (hydrogenation, hydration, polymerization)

• Alkynes: Triple bonds, undergo addition reactions

Examples and Applications

• Example of an organic compound: Propane ($C_3H_8$) is a hydrocarbon used as a fuel.

• Example of an inorganic compound: Sodium chloride ($NaCl$) is an ionic compound used as table salt.

• Application: Hydrocarbons are found in fuels (gasoline, natural gas), plastics, and pharmaceuticals.

Practice Problems (Selected)

• Classify the following as organic or inorganic compounds: $C_3H_8$, $K_3PO_4$

• Identify which properties are typical of organic or inorganic compounds: covalent bonds, gas at room temperature, produces ions in water, burns in air.

Additional info:

• Further sections in the chapter (not shown in the images) likely cover alkanes with substituents, isomerism, properties of alkanes, reactions of alkenes and alkynes, and aromatic compounds in more detail.