Introduction to Alkanes and Nomenclature

Study Notes

Introduction to Alkanes

Alkanes are a class of saturated hydrocarbons, meaning they contain only carbon and hydrogen atoms and all carbon-carbon bonds are single bonds.
They are the simplest organic compounds.
The general formula for alkanes is CnH2n+2, where 'n' represents the number of carbon atoms.
Alkanes are relatively unreactive, due to the strong C-H and C-C sigma bonds.

Nomenclature of Alkanes

Alkanes are named according to the number of carbon atoms in the longest continuous chain.
Prefixes are used to indicate the number of carbon atoms in the chain: meth- (1), eth- (2), prop- (3), but- (4), pent- (5), hex- (6), hept- (7), oct- (8), non- (9), dec- (10), etc.
Suffix -ane indicates that the compound is an alkane.
Branches (alkyl groups) are named as prefixes and their location specified by numbers.
The location of the branch is determined by the carbon atom on the main chain that the branch is attached to, with the lowest possible number being used.
Example: 2-methylpentane (a 5-carbon chain with a methyl group on the second carbon).

Isomerism in Alkanes

Isomers are compounds with the same molecular formula but different structural formulas.
Alkanes exhibit structural isomerism, where the same number of atoms arrange differently in space.
Different isomers have different physical and chemical properties.
Branched-chain alkanes have lower boiling points than straight-chain alkanes with the same number of carbon atoms (due to weaker dispersion forces).

Physical Properties of Alkanes

Alkanes are nonpolar molecules.
They are generally colorless and odorless.
They are insoluble in water, but soluble in non-polar solvents.
Boiling points increase with increasing molecular weight due to stronger London dispersion forces.
Melting points increase with increasing chain length but branches decrease melting point due to the more compact structure.

Chemical Properties of Alkanes

Alkanes are generally unreactive; they do not readily undergo reactions like addition reactions.
The dominant reaction type for alkanes is combustion (reaction with oxygen).
Alkanes undergo combustion to form carbon dioxide and water, releasing a large amount of energy.
Complete combustion requires a sufficient supply of oxygen. Incomplete combustion produces carbon monoxide (a toxic gas) and carbon soot.
Alkanes can undergo substitution reactions in the presence of light or heat with certain halogens; this reaction replaces a hydrogen atom of the alkane with a halogen atom.
The reaction with halogens is a free radical chain reaction.
Halogenation reactions are initiated by ultraviolet (UV) light or heat.

Uses of Alkanes

Alkanes are a major source of energy.
They are used as fuels (petrol, diesel, kerosene).
Alkanes are also used as raw materials for producing other chemicals.
They have various industrial applications such as solvents, waxes, and lubricants.

Important Concepts

The concept of structural formula, isomers, and the impact of structure on the physical and chemical properties of alkanes is a central and essential part of organic chemistry.

Description

This quiz covers the basics of alkanes, a class of saturated hydrocarbons that are essential in organic chemistry. You will learn about their structure, reactivity, and how to properly name these compounds using standard nomenclature rules.