1. Hydrocarbons Functional Groups
Chemistry 11
Ms. McGrath

2. Functional Groups
A functional group is a reactive group of bonded atoms that appears in all the members of a chemical family.
The functional group is the reactive part of an organic molecule. Each functional group behaves and reacts in a characteristic way. Thus, functional groups help to determine the physical and chemical properties of compounds.
For example, the reactive double bond is the functional group for an alkene.

3. Functional Groups Common Functional Groups – see page 378
Note the functional groups
Organic compounds are named according to their functional group
We have seen alkanes, alkenes, alkynes, cyclic hydrocarbons and aromatics (benzene)
We are going to look at alcohols, aldehydes, ketones, ether

4. Functional Groups
1. Compounds with the same functional group often have similar physical properties
2. Compounds with the same functional group react chemically in very similar ways

5. Functional Groups Functional groups usually contain polar bonds
Examples of these bonds are O-H, C-O, C=O
Many hydrocarbons contain C-H bonds which are weak dipoles. The several C-H bonds partially cancel each other out. There C-H bonds contribute very little to the polarity of a hydrocarbon – they are neglected when considering the polarity of the molecule

6. Physical Properties Substituted Hydrocarbons
Recall from Chapter 6, we learned about 3 intermolecular forces:
1. Hydrogen Bonds
2. Dipole Interactions
3. Dispersion Forces
** Note melting points of organic compounds follow approximately the same trend as do their boiling points **

7. Physical Properties Hydrogen Bonds
Molecules that O-H, N-H and F-H bonds, they can form hydrogen bonds with themselves and water
These molecules have higher boiling points than similar molecules that cannot form hydrogen bonds
For example, alcohols that have an O-H bond can form hydrogen bonds but alkanes cannot
Shorter chained molecules that can form hydrogen bonds are soluble in water

8. Physical Properties Dipole Interactions
Polar molecules usually have a higher boiling point than non-polar molecules of a similar size but not as high as molecules than can form hydrogen bonds
For example, ethanol, CH3CH2OH, is polar and can form hydrogen bonds. Methoxymethane, CH3OCH3, is also polar but cannot form hydrogen bonds. Ethane, CH3CH3, is non-polar and cannot form hydrogen bonds. Ethanol has the highest boiling point, then methoxymethane and ethane has the lowest.

9. Physical Properties Dispersion Forces
These are weak forces
A molecule with a greater number of carbon atoms usually has a higher boiling point than the same type of molecule with fewer carbon atoms
For example, hexane, CH3CH2CH2CH2CH2CH3, has a higher boiling point than ethane, CH3CH3

10. Physical Properties
Complete ThoughtLab – Comparing Intermolecular Forces
Page 380

11. Functional Group Alcohol
General Formula
R-OH
Where:
R represents an alkyl group
OH represents an hydroxyl group (the functional group of the alcohol family, written as –OH)

13. Alcohol