Organic Chemistry

10.1 Homologous Series (SL/HL)

This is the name given to a group of compounds that can be described by a general formula.

Name Alkanes Alkenes Alcohols

General CnH2n+2 CnH2n CnH2n+2O

Examples CH3CH3 CH2CH2 CH3CH2OH
      CH3CH2CH3             CH2CHCH3         CH3CH2CH2OH

      All members of a homologeous series have similar chemical properties.

      The next member in a homologeous series differs by a –CH2- group (called a repeating unit).

    • This causes a gradual change in physical properties as the chain length increases. (see below)

10.1 Physical Properties in Homologous Series

• Boiling Point increases as chain length increases.

• This is due to an increase in Van De Waal forces between the molecules as the molar mass (and surface area) increases.

10.1 Representing Organic Structures

Organic structures can be represented in a variety of ways:

Empirical Formula: Simplest ratio of atoms of each elements in a compound.

E.g. Pentene: Empirical Formula = CH2

Molecular Formula: Actual numbers of atoms of each element present in the compound.

E.g. Pentene: Molecular Formula = C5H10

Structural Formula: How the atoms are arranged in the molecule.

Condensed structural formula shows the position of the atoms but omits the bonds.

E.g. Propene: CH2=CHCH2CH2CH3   or     CH2CH(CH2)2CH3

Full structural formula/graphic formula/displayed formula = Shows every atom and bond.

E.g. Propene: H H     H     H H

                    C=C   -   C   -   C   - C -   H

                H       H     H     H     H

Show the condensed structural formula and the full structural of the following molecule:

Hexane: Molecular formula = C6H14

TOK: Why is it necessary to use different types of formula to represent organic molecules?

10.1 Functional Groups (SL/HL)

    • The functional group is the reactive...