Review Alkanes C n H 2n+2 C 4 H 10 a) ethane b) propane c) butane d) pentane CH 3 (CH 2 )CH 3 butane 2

Newman projections butane staggered eclipsed stable

Nomenclature heptane branches 2 324

Nomenclature methyl ethyl propyl ethyl 3,5-diethyl ethyl propyl methyl 3,5-diethyl-2-methyl-4-propylheptane

Cycloalkanes linear alkanes branched alkanes cycloalkanesclosed ringsC n H 2n bond angle = 60 o tetrahedral angle = 109 o very unstable propane C n H 2n cyclo

Cycloalkanes cyclobutane bond angle = 88 o tetrahedral angle = 109 o unstable

Cycloalkanes cyclopentane bond angle = 108 o tetrahedral angle = 109 o stable

Cycloalkanes 1,3-dichlorocyclobutanecis- trans- 1,3-dichlorocyclobutane geometric isomers -- --

Cycloalkanes cyclohexane predicted bond angle = 120 o tetrahedral angle = 109 o stable

cyclohexane chair conformation boat conformation stable unstable axial positions equatorial positions crowded only H largerlarger groups

cyclohexane cis-cis-1,2-dimethylcyclohexane trans-trans-1,2-dimethylcyclohexane axial-equatorial equatorial-equatorial axial-axial 1,2-dimethylcyclohexane 1,2-dimethylcyclohexane

Optical isomerism bromo * * trans- * * chloroiodomethane hexane cyclopentane1,3-dibromocyclopentane no C* C* =C* = Stereocenter 4 different substituents 3-methyl

Alkane Summary 1. Alkanes - sp 3 hybridized 2. Relatively unreactive Substitution with halogens Combustion 3. Non-polar IMF = London Dispersion Forces size structure

4. Free rotation around C-C bonds conformations 5. Non-cyclic alkanes - structural isomers 6. Cyclic alkanes - geometric isomers cis-, trans- 7. Alkanes - optical isomers stereocenters C* C*