Hydrocarbons

Read pp. 180-190

HydrocarbonsCompounds that contain ONLY hydrogen and carbon atoms. There are three kinds of hydrocarbons:

Alkanes – single bond between carbon atoms

Alkenes – one or more of the carbons have double bond(s)

Alkynes – one or more of the carbons have triple bond(s)

# of C atoms Prefix Alkane IUPAC Name

1 meth- methane

2 eth- ethane

3 prop- propane

4 but- butane

5 pent- pentane

6 hex- hexane

7 hept- heptane

8 oct- octane

9 non- nonane

10 dec- decane

Structural Formulas for Alkanes

1. Draw the # of C atoms in a straight line according to prefix

2. Fill in the hydrogen atoms using single bond lines. Remember, Carbon has 4 valence electrons, so it holds 4 bonds!!

ethane octane

Naming Alkanes

1. Count the # of carbon atoms prefix2. Write in the suffix “ane” (single-bonds

only)

butane heptane

Structural Formulas – Alkenes and Alkynes

1. Draw the # of C atoms in straight line according to prefix

2. The number in front of the IUPAC name tells you which C atom the double/triple bond is located.

3. Fill in the H atoms. Remember, each C atom has 4 bonds, so double-check!

2-hexene 1-pentyne

Naming Alkenes and Alkynes

1. Look at the structural formula. A double bond tells you it’s an alkene. A triple bond tells you it’s an alkyne.

2. Count # of C atoms prefix

3. Read left-right and right-left. Take the lowest # that the C atom is located on. This # goes in front of prefix

4. Write ‘ene’ if alkene or ‘yne’ if alkyne.

Naming Alkenes and Alkynes

H H H H

H-C-C-C-C=C-H 1-pentene

H H H

H H H H H H

H-C-C-C-C-C≡C-C-C-H 3-octene

H H H H H H

Isomers

Compounds that have the SAME molecular formula (eg. C4H8), but have different shapes. This leads to differences in chemical and/or physical properties.

1-pentene 2-pentene

BP: 30°C BP: 37°C

Properties of Hydrocarbons

• Alkanes are saturated. It cannot accept any more atoms/molecules.

• Alkenes and alkynes are unsaturated. Their double/triple bonds can be broken down to accept more atoms/molecules (see Addition Reactions)

• The longer the hydrocarbon (more C atoms), the more energy it takes to break it apart.

• The more C atoms, the higher the boiling point.

Combustion Reactions of Hydrocarbons

When a hydrocarbon reacts with oxygen gas to form two products: CO2 and H2O.

Write a balanced equation to show the combustion of 1-pentane.

C5H12 + 8O2 5CO2 + 6H2O

Addition Reactions of Alkenes and Alkynes

When a compound is added across a double or triple bond. This compound can be:

• A halogen (HCl, HBr, HI, HF)• Water (H2O)• Hydrogen gas (H2)

Note: The double bond becomes a single bond; the triple bond becomes a double bond.

Draw a structural formula equation for the addition reactions:

a) 2-butene and hydrogen bromine (HBr)

H H H H H H H H

H-C-C=C-C-H + H-Br H-C-C-C-C-H

H H H H Br H

a) 2-pentyne and water (H2O)

H H H H H H

H-C-C≡C-C-C-H + H-OH H-C-C=C-C-C-H

H H H H H OH H H

c) 2-heptene and hydrogen gas (H2) H H H H H H H H H H H H H H

H-C-C=C-C-C-C-C-H + H-H H-C-C-C-C-C-C-C-H

H H H H H H H H H H H H