Lesson 5-2 Cycloalkanes Alkanes that form rings are called cycloalkanes. Cyclopropane and cyclobutanes are strained because the C-C-C bond angles in the ring are less than 109.5 required for the tetrahedral geometry. Because of the strain in the ring, cyclopropane is very reactive.

Examples – Name the following: 1. cyclohexane 2. cycloheptane

Substituted Cycloalkanes Examples: Name each compound 1-ethyl-4-methylcycloheptane 2-ethyl-1,1-dimethylcyclobutane

Unsaturated Hydrocarbons Unsaturated hydrocarbons contain double bonds or triple bonds between carbon atoms. For each double bond, there are two less hydrogen atoms (than CnH2n+2) For each triple bond, there are four less hydrogen atoms (than CnH2n+2)

Alkenes – contain C=C double bond(s). Named like alkanes, except the ending is changed to “ene.” You must number the carbon atom on which the double bond “begins.” Example: Pent-2-ene What is the formula? More Examples 2-methylhex-2-ene 5-ethyl-3-methylhept-2-ene

Alkynes – contain C=C triple bond(s). Named like alkanes, except the ending is changed to “yne.” You must number the carbon atom on which the triple bond “begins.” Example: Hex-2-yne Another Example: 2,6-dimethyloct-3-yne

Properties of Unsaturated Hydrocarbons Alkenes and alkynes are generally nonpolar, and contain only LDF. A carbon atom bonded to four other atoms has tetrahedral geometry. A carbon atom bonded to three other atoms has trigonal planar geometry. A carbon atom bonded to two other atoms has linear geometry.

Functional Groups Some organic molecules contain elements other than just C and H. The parts of the molecules that are elements other than C and H are called functional groups. Alcohols – contain –OH in place of one or more hydrogen atoms. Named like the hydrocarbon on which they are based (# C atoms), with –ol in place of the e. Begin with the number of the C that contains the OH

Examples – Name the following alcohols ethanol 1-hexanol 2-methyl-3-hexanol

Reactions of Alcohols 1. Oxidation – warmed with acidified dichromate (Cr2O72-) Primary alcohols (C with OH is attached to one other C) oxidized to aldehydes, then to carboxylic acids. Secondary alcohols (C with OH is attached to 2 other C) oxidized to ketones Tertiary alcohols (C with OH is attached to 3 other C – no H atoms attached to C with OH) cannot be oxidized by dichromate

Dehydration (in concentrated sulfuric or phosphoric acid) – produces a double bond (opposite of addition of water)