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

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

3. Nomenclature heptane heptane heptane 3 branches 2 branches 4 branches1 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

4. Nomenclature 3,5-diethyl -2-methyl -4-propyl heptane 2- methyl methyl1 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

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

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

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

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

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

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

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

12. Optical isomerism
C* =
Stereocenter
4 different
substituents *

13. 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

14. 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

15. 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

16. 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*

17. Alkane Summary 1. Alkanes - sp3 hybridized 2. Relatively unreactive
Substitution with halogens
Combustion
3. Non-polar
IMF = London Dispersion Forces
size
structure

18. 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*