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

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

3. 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

4. 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

5. 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

6. 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*

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

8. 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*

9. + alkyl halides uv Cl2 .. 2 :Cl. :Cl:Cl: half-arrow = 1e- step 1 ..
form mostly
stability of free radicals
3o > 2o > 1o

10. * * 3-methylhexane no reaction stereocenter C+ electrophile
+ OH- *
stereocenter *
+ OH-
+ Br-
C+ +
electrophile
e- deficient .. - :
OH-
nucleophile
e- rich ..

11. Nucleophilic Substitution SN1* *
+ OH-
+ Br-
reaction is 1st order in C7H15Br
zero order in OH-
reactants are optically active
rate = k [R – X]
products are optically inactive

12. Nucleophilic Substitution SN1
rate determining step unimolecular
C2H5 – C – Br
CH3
C3H7 :
. .
C2H5 – C Br-
CH3
C3H7 :
. .
step 1
slow C+
carbocation
(4 – ½ (6) – 0) = +1
reactants are optically active
rate = k [R – X]
products are optically inactive

13. Nucleophilic Substitution SN1
C2H5 – C – Br
CH3
C3H7 :
. .
C2H5 – C Br-
CH3
C3H7 :
. .
step 1
slow C+
CH3
C3H7
C2H5
H – O - :
. .
- O – H :
. .
step 2
CH3 HO
C2H5
C3H7
CH3
H7C3
C2H5 OH * *
reactants are optically active
rate = k [R – X]
products are optically inactive

14. Nucleophilic Substitution SN1Ea
carbocation intermediate E
1st order in R – X
2 products
Nu-
+ R – X
Nu – R + X-

15. Nucleophilic Substitution SN2 * *
+ OH-
+ Br-
reaction is 1st order in C4H9Br
1st order in OH-
rate = k [R – X]
[OH-]
reactants are optically active
products are optically active

16. Nucleophilic Substitution SN2
rate determining step bimolecular
C – Br H
C2H5 :
. .
CH3
---C---Br H
C2H5 :
. .
CH3
H-O
HO – C – CH3 H
C2H5
H – O - :
. .
step 1
:Br: -
. . *
slow
transition state
C2H5 H
CH3 Br
C2H5 HO
CH3 H
stereocenter inverted
reactants are optically active
rate = k [R – X][OH-]
products are optically active

17. Nucleophilic Substitution SN2
Nu---C---X
 -
SN2 Ea E
1st order in R – X
1st order in Nu-
1 product
Nu-
+ R – X
Nu – R + X-

18. SN1 or SN2 SN1 carbocation 3o > 2o > 1o 3o R –X yes 2o R –X ?H H R R R
SN1
carbocation
3o > 2o > 1o
3o R –X
yes
2o R –X ?
1o R –X no

19. SN1 or SN2
1o R – X
yes
SN2
transition state
2o R –X ?
3o R – X no

20. SN1 or SN2
SN1
3o R –X
yes
SN2
1o R – X
yes
2o R –X ?
2o R –X ?
1o R –X no
3o R – X no
Other factors influencing rates:
Nucleophile :
charged
OH-
SH- I-
CN-
neutral
H2O
NH3
Solvent
Temperature