THE SHAPE OF CYCLOALKANES

THE SHAPE OF CYCLOALKANES (continued)

NAMING CYCLOALKANES Cycloalkanes are alkanes containing rings of carbon atoms. The prefix cyclo- is used before the alkane name. When two or more substituents are attached to the cycloalkanes, the ring numbering begins with the first group alphabetically and proceeds to give lowest numbers possible. Example: CH 2 CH CH 3 1-ethyl-3-methylcyclopentane

ISOMERISM & CYCLOALKANES Stereoisomers are compounds with the same structural formula but different spatial arrangements of atoms. Geometric isomers are molecules with restricted rotation around C-C bonds that differ in the three-dimensional arrangements of their atoms in space and not in the order of linkage of atoms. Rotation about C-C single bonds occurs in open-chain compounds but not within rings.

ISOMERISM & CYCLOALKANES (continued) Geometric isomerism can result in two geometric isomers of 1,2-dimethylcyclopentane. Cis-substituents on the same side. Trans-substituents on the opposite side.

PHYSICAL PROPERTIES OF ALKANES Non-polar molecules with weak intermolecular forces Not soluble in water (hydrophobic) Low density (less dense than water) Melting points increase with molecular size Boiling points increase with molecular size

PHYSICAL PROPERTIES OF ALKANES (continued) A homologous series is a group of compounds with the same functional class that differ by a –CH 2 – group.

PHYSICAL PROPERTIES OF ALKANES (continued)

ALKANE REACTIONS Alkanes are the least reactive of all organic compounds. The most significant reaction of alkanes is combustion (rapid oxidation). Many alkanes are used as fuels. Methane – natural gas Propane – used in gas grills Butane – lighters Gasoline – a mixture of hydrocarbons

ALKANE REACTIONS (continued) Complete Combustion (in the presence of adequate oxygen) Incomplete Combustion (not enough oxygen available) CH 4 + 2O 2 → CO 2 + 2H 2 O kcal/mol 2CH 4 + 3O 2 → 2CO + 4H 2 O CH 4 + O 2 → C + 2H 2 O