Functional Groups and Homologous Series

Introduction to Organic Chemistry

Define a functional group.

An atom or group of atoms in a molecule that is responsible for its characteristic chemical reactions.

What does the functional group of an organic compound determine?

Its characteristic chemical reactions and properties.

Give an example of a functional group.

The –COOH functional group in carboxylic acids.

Which functional group is present in HCOOH, CH₃COOH and CH₃CH₂COOH?

The –COOH carboxylic acid functional group.

Why do compounds with the same functional group have similar chemical properties?

The functional group is responsible for their characteristic chemical reactions.

Define a homologous series.

A family of compounds with the same functional group in which successive members differ in formula by CH₂.

What do members of the same homologous series have in common?

They have the same functional group and similar chemical properties.

By what unit do successive members of a homologous series differ?

CH₂.

How does the molecular formula change from one member of a homologous series to the next?

One carbon atom and two hydrogen atoms are added, CH₂.

What happens to the physical properties along a homologous series?

They show a gradual change.

What happens to the chemical properties within a homologous series?

They are similar because the compounds contain the same functional group.

Are alkanes a homologous series?

Yes.

What is the general formula of an alkane?

CₙH₂ₙ₊₂.

What is the general formula of an alkene?

CₙH₂ₙ.

What is the general formula of a halogenoalkane?

CₙH₂ₙ₊₁X, where X represents a halogen.

What is the general formula of an alcohol?

CₙH₂ₙ₊₁OH.

What does n represent in a general formula?

The number of carbon atoms.

What does X represent in the general formula of a halogenoalkane?

A halogen atom.

What is a general formula?

A formula that represents all the members of a homologous series.

Why are general formulae useful?

They allow the formula of any member of a homologous series to be determined from its number of carbon atoms.

What is the molecular formula of an alkane containing one carbon atom?

CH₄.

What is the molecular formula of an alkane containing two carbon atoms?

C₂H₆.

What is the molecular formula of an alkane containing three carbon atoms?

C₃H₈.

What is the molecular formula of an alkane containing four carbon atoms?

C₄H₁₀.

What is the molecular formula of an alkane containing five carbon atoms?

C₅H₁₂.

What is the simplest alkane?

Methane, CH₄.

What products are formed when an alkane undergoes complete combustion in air?

Carbon dioxide and water.

What is the equation for the complete combustion of methane?

CH₄ + 2O₂ → CO₂ + 2H₂O.

What is the equation for the complete combustion of propane?

C₃H₈ + 5O₂ → 3CO₂ + 4H₂O.

Why do different alkanes undergo similar chemical reactions?

They belong to the same homologous series and have similar chemical properties.

What trend is seen in the boiling temperatures of alcohols as carbon chain length increases?

The boiling temperature increases.

What is the boiling temperature of CH₃OH shown in the table?

65°C.

What is the boiling temperature of CH₃CH₂OH shown in the table?

79°C.

What is the boiling temperature of CH₃CH₂CH₂OH shown in the table?

97°C.

What is the boiling temperature of CH₃CH₂CH₂CH₂OH shown in the table?

117°C.

What happens to boiling temperature as the number of carbon and hydrogen atoms in an alcohol increases?

The boiling temperature increases.

How do the boiling temperatures of alcohols demonstrate a property of a homologous series?

They show a gradual change in physical properties as chain length increases.

What three key features should you remember about a homologous series?

Same functional group, similar chemical properties, and successive members differ by CH₂.

What is the difference between a functional group and a homologous series?

A functional group is the atom or group of atoms responsible for characteristic reactions; a homologous series is a family of compounds containing the same functional group.