1. Structure and Properties
Hydrocarbons
Structure and Properties

2. Hydrocarbons Alkanes Alkenes- have one or more C=C double bonds
single C-C bonds
if all C’s have H’s attached molecules are called saturated hydrocarbons
Alkenes- have one or more C=C double bonds
Alkynes- have one or more CΞC triple bonds
alkenes & alkynes are called unsaturated hydrocarbons because they have fewer than the maximum possible number of H atoms

3. Hydrocarbons
can form either a straight chain or a cyclic (ring) structure
hydrocarbons which are attached to the main structure are called alkyl groups and are named according to the number of carbons

4. Hydrocarbons
a 4th group are the aromatic hydrocarbons which have a unique ring structure
simplest is benzene and all others are derivatives of benzene

5. Physical Properties of Alkanes

6. Alkanes are insoluble in water
Solubility
Alkanes are insoluble in water
This is because water molecules are polar, whereas alkanes are non-polar (all the C - C and C - H bonds are nearly purely covalent)
The O - H bond in a water molecule is highly polar due to the high electronegativity of oxygen δ-
H O H
δ δ+

7. Solubility
The hydrogen atoms in one water molecule are strongly attracted to the oxygen atoms in other water molecules, and the small size of the H atoms allows the molecules to approach each other very closely.
This special attraction is called hydrogen bonding
Due to alkanes non- polar nature they do not mix with the polar water molecule.

8. Similar hydrocarbons are found in beeswax
Solubility
The mutual insolubility of alkanes and water is used to advantage by many plants.
Alkanes often make up part of the protective coating on leaves and fruits (C27H56 and C29H60).
Similar hydrocarbons are found in beeswax
The major function of plant waxes is to prevent water loss from the leaves and fruit.

9. This is due again to alkanes being non-polar.
Boiling Points
Alkanes have lower boiling points than most other organic molecules with a similar weight.
This is due again to alkanes being non-polar.
Alkane molecules are only held together by weak intermolecular forces called van der Waals attractions (London forces).
Electrons are always moving and sometimes for a instant they can be unevenly distributed in a molecule and cause temporary dipole (positive and negative end).

10. Boiling Points
These attractions are weak, so the process of separating the molecules (boiling) from one another requires little energy.

11. Boiling Points
Since these attractive forces can only operate over short distances between the surface of molecules:
The boiling points of alkanes rise as the chain length increases and fall as the chains become branched.

12. Boiling Points
Note: In a homologous series there is a gradual increase in boiling point as the number of carbon atoms increases, for the very same reason.
Organic compounds in the a
homologous series vary by -CH2