1. Reactions of Hydrocarbons
Alkanes, alkenes, alkynes and aromatics

2. Types of Hydrocarbons Hydrocarbons contain C and H
There are 4 families, alkanes only have C-C single bonds, alkenes have at least one C=C and alkynes have a least one CΞC bond, aromatics are like cyclohexane with 3 C=C double bonds

3. Names of Alkanes
The names all end in “ane”, the prefix depends on how many carbons are in the alkane

4. Cycloalkanes In a cycloalkane a group of C atoms form a ring
Consider Cyclobutane C4H8
Complete Structural
Formula
Geometric
Formula
Condensed
Formula
3-dimensional
structure

5. Nomenclature for Alkenes
Alkenes have one or more C=C
Step 1: Name the longest chain with the C=C in it
Step 2: Number the longest chain so that the carbons in the C=C have the lowest numbers
Step 3: Locate the lowest numbered C in the C=C
Step 4: Locate and name attached groups
Step 5: Combine the names

6. Naming Alkenes 2 carbons prefix eth- 1 C=C suffix –ene Name = ethene
3 carbons prefix prop-
1 C=C suffix –ene
Name = propene
4 carbons prefix but-
1 C=C suffix –ene
Name = butene
But where is the C=C?
1 butene (or but-1-ene)
2 butene (or but-2-ene)

7. Naming Cycloalkenes 6 carbons prefix hex- 1 C=C suffix –ene
Name = hexene
6 carbons in a ring
cyclohexene
5 carbons prefix hex-
1 C=C suffix –ene
Name = pentene
5 carbons in a ring
cyclopentene

8. Naming Alkynes 2 carbons prefix eth- 1 CΞC suffix –yne Name = ethyne
3 carbons prefix prop-
1 CΞC suffix –yne
Name = propyne
4 carbons prefix but-
1 CΞC suffix –yne
Name = butyne
But where is the CΞC?
1 butyne (or but-1-yne)
2 butyne (or but-2-yne)

9. Aromatics Aromatics contain This is called benzene
This is called toluene (methyl benzene)

10. Identifying the type of hydrocarbon
Alkanes, alkenes, alkynes and aromatics have different chemical properties and we can identify what we have by performing 3 tests
Reaction with O2 (combustion)
Reaction with Br2 (Bromine test)
Reaction with KMnO4 (Potassium Permanganate test)

11. Reaction with O2 (combustion)
All hydrocarbons react with O2 to make CO2 (with some CO and C) and H2O
CH4 + 2O2  CO2 + 2H2O
(one CO2 for every C and one H2O for every 2H)
If all hydrocarbons react how can this tell us if we have an alkane, alkene, alkyne or aromatic?
Heavier hydrocarbons (more C) don’t evaporate as easily so less easy to combust
Alkynes, Aromatics and cycloalkanes and cycloalkenes burn with sooty flames
Ethyne (acetylene)
aromatic
methane
cyclohexene

12. Reaction with Br2 (Bromine test)
Add
alkane or alkene
Alkane
Alkene
Alkenes and alkynes quickly react with Br2 to make haloalkanes (colorless)
Alkanes don’t react (except slowly in bright light)
Benzene doesn’t react toluene will
Br2 water

13. Reaction with KMnO4 (Potassium Permanganate test)
In this test KMnO4 (purple) reacts with alkenes but not alkanes or aromatics
Alkane or aromatic (negative test)
Alkene (positive test)
alkene
diol

14. The Experiment
Make models for ethene, propene, cyclobutene, cis-2-butene and ethyne and draw them
In fume hood combust 5 drops of cyclohexane, cyclohexene, toluene and your unknown, record observations
In the fume hood add 3-4 drops Br2 solution to 15 drops of cyclohexane, cyclohexene, toluene and your unknowns, record observations, then move to a window (direct light)
To 5 drops of cyclohexane, cyclohexene, toluene and your unknown add 15 drops of 1% KMnO4 record your observations
From your results identify your unknown as an alkane, or an alkene