Review Alkanes CnH2n+2 C4H10 CH3 (CH2) CH3 2

Newman projections 1 2 3 4 1 2 3 4 staggered eclipsed stable

Nomenclature heptane heptane heptane 3 branches 2 branches 4 branches 1 2 1 3 7 3 1 3 5 7 4 6 4 2 4 6 5 2 5 6 7 heptane heptane heptane 3 branches 2 branches 4 branches

Nomenclature 3,5-diethyl -2-methyl -4-propyl heptane 2- methyl methyl 1 2 2- methyl methyl 3- ethyl 3 5 7 4 6 4- ethyl propyl propyl 5- ethyl 3,5-diethyl 3,5-diethyl -2-methyl -4-propyl heptane

Cycloalkanes linear alkanes CnH2n+2 branched alkanes cycloalkanes closed rings CnH2n 2 cyclo propane 3 1 bond angle = 60o tetrahedral angle = 109o very unstable

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

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

Cycloalkanes geometric isomers cis- 1,3- dichloro cyclo butane trans- - - cis- 1,3- dichloro cyclo butane trans- 1,3- dichloro cyclo butane

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

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

cyclohexane cis- 1,2- dimethyl cyclo hexane axial-equatorial trans- 1,2-dimethylcyclohexane trans-1,2-dimethylcyclohexane axial-axial equatorial-equatorial

Optical isomerism C* = Stereocenter 4 different substituents *

non-superimposable mirror images * C Br I Cl H C * Br Cl I H Fischer projections (+) (-) Br * Br H Cl I Enantiomers I * Cl H non-superimposable mirror images

Enantiomers identical in most properties differ in: 1.interaction with polarized light 2. interaction with chiral environments Light interacts with molecules when it passes through them [interaction of electrical fields] When light encounters mirror image of molecule, interaction is reversed

Polarized light (-) One enantiomer - rotate light to the left (+) Other enantiomer - rotate light to the right in 50/50 mix - no net rotation racemic mixture one enantiomer - polarized light will be rotated optical activity

Optical isomerism 3-methyl hexane bromo chloro iodo methane bromo Stereocenter 4 different substituents * * 3-methyl hexane bromo chloro iodo methane * * bromo cyclo pentane trans- 1,3-dibromo cyclopentane no C*

Alkane Summary 1. Alkanes - sp3 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*