1. Functional Groups

2. What are functional groups?
Remember back to alkenes and alkynes
A group of bonded atoms that appear in all members of a chemical family
The functional group results in similar properties for all members of the group.
Ex. 2 – propanol (isopropanol) and ethanol have very similar properties due to the (-OH) hydroxyl group.

3. General Formulas
General formulas for organic compounds emphasize the functional group.
Why?
Functional groups are most important.
How?
R- stands for the alkyl group(part) of the molecule
If more than one type alkyl group is present we use R’ and R” to tell show that they are different

4. General Formulas Eg. The general formula for alcohols is:
R-OH, where R- represents the hydrocarbon or alkyl part
Therefore, R-OH represents ALL alcohols
CH3OH
CH3CH2OH
CH3CH2CH2OH, etc.

5. Naming Organic Compounds
According to functional group
This determines properties
Suffix – indicates the most important functional group
Eg. Ethene = double bond
Ethanol = hydroxyl group

6. Physical Properties and Forces Between Molecules

7. Physical Properties of Organic Compounds
Melting Point
Boiling Point
Solubility
All depend on functional groups
Same functional group = similar properties
Why?
Physical properties are determined by intermolecular forces = forces b/n molecules

8. Intermolecular Forces
3 types play a role
Hydrogen bonding
Dipole-dipole interactions
Dispersion forces
Decreasing Strength

9. Hydrogen Bonding
Attraction between the H atom from an N-H, O-H or F-H group on one molecule and a N, O or F atom on another molecule.
E.g. Hydrogen bonding in H2O

10. Dipole-dipole Interactions
Attractive force b/n polar molecules.
Cause polar molecules to stick together.
Weaker than H bonding b/c electronegativity difference is less within the covalent bond.
E.g.

11. Dispersion Forces (London or Van der Waals Forces)
Weak attractive force
Occurs between all covalent molecules
as the size of the molecule 
How are they created?
Random, uneven electron distribution occurs within molecules that come close to one another.
Weak attraction b/n nucleus of one molecule and electrons of the other.

12. Predicting Properties based Intermolecular Forces

13. Can the molecules form hydrogen bonds?
Must have O-H, N-H, H-F
Can form H-bonds with themselves and H2O
Molecules can form H-bonds with themselves = higher boiling point
If they can form H-bonds with water they will usually be soluble in water.

14. Are the molecules polar?
They are if:
They have polar bonds
The polar bonds do not counter act each other
ie. They act in opposite directions

15. Polar Molecules Are attracted to each other by dipole-dipole forces
Have lower boiling points than similar molecules with hydrogen bonding but higher than non-polar molecules.
As non-polar part of a molecule gets larger  solubility decreases.
Eg. CH3CH2OH is more soluble than CH3CH2CH2CH2OH

16. Relative boiling points
CH3CH2OH – ethanol (hydrogen bonds, dipole-dipole and dispersion)
CH3OCH3 – methyoxymethane (dipole-dipole and dispersion)
CH3CH3 – ethane (dispersion forces)
Why?
Molecules need more kinetic energy to break the intermolecular forces.
Boiling Point

17. How strong are the dispersion forces?
Weakest of the 3
Stronger as the hydrocarbon part of the molecule gets larger
Therefore longer molecules tend to have higher boiling points
Eg. ethane (-89°C)
hexane (69°C)