Reactions of Hydrocarbons Alkanes, alkenes, alkynes and aromatics

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

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

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)

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 6 carbons in a ring cyclopentene

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)

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

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 O 2 (combustion) Reaction with Br 2 (Bromine test) Reaction with KMnO 4 (Potassium Permanganate test)

Reaction with O 2 (combustion) All hydrocarbons react with O 2 to make CO 2 (with some CO and C) and H 2 O CH 4 + 2O 2  CO 2 + 2H 2 O (one CO 2 for every C and one H 2 O 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 aromatic Ethyne (acetylene) methane cyclohexene

Reaction with Br 2 (Bromine test) AlkaneAlkene Br 2 water Add alkane or alkene Alkenes and alkynes quickly react with Br 2 to make haloalkanes (colorless) Alkanes don’t react (except slowly in bright light) Benzene doesn’t react toluene will

Reaction with KMnO 4 (Potassium Permanganate test) In this test KMnO 4 (purple) reacts with alkenes but not alkanes or aromatics Alkane or aromatic (negative test) Alkene (positive test) alkenediol

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 a 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% KMnO 4 record your observations From your results identify your unknown as an alkane, or an alkene