HYDROCARBONS

Hydrocarbons are composed, as their name suggests mainly of carbon and hydrogen atoms, though some types have oxygen, nitrogen or sulphur atoms. Hydrocarbons are divided into two groups, Aliphatics or Aromatics. Most hydrocarbons are aliphatics.

Representing Hydrocarbon There are four ways in which hydrocarbons can be represented. 1. Chemical Formula We are used to using chemical formulas to represent compounds. Unfortunately, chemical formulas are not useful when dealing with organic molecules because the arrangement of the atoms within the molecule is important. This can be seen with the sugars glucose and fructose.

Comparison of glucose and fructose

2. Structural formulas are very useful and important in organic chemistry. A structural formula shows both the type and arrangement of the elements and all bonds.

3. Condensed formulas show major bonds but normal C to H bonds are not drawn. CH 3 CH 2 CH 2 CH 2 CH 3 4. Line diagrams represent the molecule using lines. The end of a line means CH 3 while a corner is CH 2

ALKANES Alkanes area class of HYDROCARBONS which contain only carbon and hydrogen. Two other terms which describe alkanes are saturated and paraffins.HYDROCARBONS Alkanes are SATURATED which means that each carbon is bonded to four other atoms through single covalent bonds. Hydrogen atoms usually occupy all available bonding positions after the carbons have bonded to each other. PARAFFINS which is derived from a Latin word meaning "little activity", and means that the compounds are very unreactive. The general structure is C n H 2n+2

Two common alkanes

Properties Physical Properties Boiling points depend on chain length. The longer the chain the higher the boiling temperature Boiling points Non polar Insoluble in water Chemical Reactivity No functional groups, saturated, and class name of paraffins which means - Unreactive to other chemicals. All compounds: Combustion ReactionCombustion Reaction

ROOT ALKANE NAMES Root names give the number of carbons in the longest continuous chain. Root names are used with various "endings" to indicate branches, type of bonds between carbons, and functional groups. The following list gives the most basic root the with normal hydrocarbon alkane endings for the number of carbons in the longest continuous chain. Memorize this list. Example: root = "eth" + alkane ending = "ane" = ethane

No. of Carbons Root Name Formula C n H 2n+2 Structure 1 methane CH 4 2 ethane C 2 H 6 CH 3 CH 3 3 propane C 3 H 8 CH 3 CH 2 CH 3 4 butane C 4 H 10 CH 3 CH 2 CH 2 CH 3 5 pentane C 5 H 12 CH 3 CH 2 CH 2 CH 2 CH 3

No. of Carbons Root Name Formula C n H 2n+2 Structure 6 hexane C 6 H 14 CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 7 heptane C 7 H 16 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 8 octane C 8 H 18 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 9 nonane C 9 H 20 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 10 decane C 10 H 22 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3

Cycloalkanes Cycloalkanes contain a carbon chain that is in the form of a ring. Each cycloalkane has a formula that is 2H less than the corresponding alkane. For example, propane is C 3 H 8 whereas cyclopropane is C 3 H 6. Butane is C 4 H 10 and cyclobutane is C 4 H 8. The names of the cyclic structures use the prefix cyclo in from of the alkane name for the carbon chain. Timberlake LecturePLUS

Timberlake LecturePLUS Cycloalkanes Cyclopropane CH 2 CH 2 CH 2 Cyclobutane CH 2 CH 2 CH 2

Timberlake LecturePLUS More Cycloalkanes Cyclopentane CH 2 CH 2 CH 2 CH 2 Cyclohexane CH 2

Timberlake LecturePLUS Naming Cycloalkanes with Side Groups Number of Naming side groups OneSide group name goes in front of the cycloalkane name. TwoNumber the ring in the direction that gives the lowest numbers to the side groups and add the number to the name.

Timberlake LecturePLUS Cycloalkanes with Side Groups

ISOMERS Isomers are compounds which have the same formula but have different forms. Some isomers are known as Structural Isomers because they have a completely different atomic arrangement, while others are called Geometric Isomers because of the spacial arrangement.

Isomers of C 4 H 10 Butane2-Methylpropane

Reaction of Alkanes Alkanes are very unreactive in most cases. The exceptions are Combustion and Halogenation. Alkanes readily react with oxygen in combustion reactions to form carbon dioxide and water. The shorter chain alkanes are the ones which we normally think of as fuel such as Methane (natural gas), propane for bbqs, butane for lighters and octane for the car.

Halogenation involves the reaction of the alkane with a halogen such as F 2, Cl 2, Br 2, or I 2. The product is an alkyl halide in which a H is replaced by a halogen atom. If the halogen is in excess the reaction contiunes until all H are replaced.

CH 4 + F 2 → CH 3 F + HF Fluromethane CH 3 F + F 2 → CH 2 F 2 + HF Difluoromethane CH 2 F 2 + F 2 → CHF 3 + HF Trifluoromethane CHF 3 + F 2 → CF 4 + HF carbon tetrafluoride