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1

Gibbs free energy of alkene reactions

Enthalpy favors alkene to alkane reactions

At higher temperatures, entropy favors the reverse (alkene to alkane) reactions

2

Electrophilic addition to alkenes overall mechanism

H of acid attacks less substituted carbon

Carbocation forms

Initial leaving group attacks the carbocation

3

regioselectivity of electrophilic addition to alkenes

H goes to less substituted carbon

Oftentimes, a halogen goes to the more substituted carbon

4

stereoselectivity of electrophilic addition to alkenes

there isn't any

the halogen can attack the carbocation from either top or bottom, resulting in 2 enantiomers being formed

5

What does hydration of an alkene require?

Acid catalyst

6

Why does hydration require an acid catalyst?

Protonate H2O, so that OH- is not the initial leaving group

7

Is hydration reversible?

Yes through E1 reactions

8

E1 reaction

leaving group leaves and carbocation is formed

then nucleophile deprotonates H from other carbon and alkene is formed

9

Hydration overall mechanism

Acid protonates H2O

H3O+ deprotonates alkene and forms carbocation

H2O attacks carbocation

H2O deprotonates alkane to make neutral

Neutral alkane and H3O+ are formed

10

Regioselectivity of hydration

The -OH group will be added to the more substituted carbon due to more substituted carbon having the cation that H2O attacks

11

Markovinkov alcohol

-OH group is added to more substituted carbon

12

When are markovinkov alcohols seen?

Hydration

Halogenation with a nucleophilic solvent

13

Stereoselectivity of hydration

there isn't any

H2O can attack the carbocation from either top or bottom

14

How does an acid catalyst lower the LUMO of H2O?

Makes the LUMO sigma*O+ H

The + charge on oxygen means that there is a greater Zeff and the orbital's energy will be lowered, making a lower LUMO

15

Solvent of halogenation

Nucleophilic or non-nucleophilic solvent matters

16

Regioselectivity of halogenation?

None seen with a non-nucleophilic solvent

Nucleophilic solvent will only attack the more substituted carbon since halonium cation intermediate creates a slight positive charge on the more substituted carbon

17

Halonium cation

intermediate in halogenation where there is a positively charged halogen intermediate

18

Stereoselectivity of halogenation?

Nucleophile will only attack anti- in second step since this is where the sigma* lobe is exposed

Similar to a SN2 reaction

19

What does anti- attack in halogenation produce?

Only the trans- configuation

Syn would result in the cis- configuration (Meso) which we don't see

20

LUMO of halogenation

Sigma* Br-Br or Sigma* Cl-Cl

Great LUMOs because of:
1) low starting position on MO diagram
2) poor overlap of bulky orbitals

21

Peroxycarboxlyic acid LUMO

O-O is a low lumo due to initial low starting energy

22

Is expoxidation concerted? What indicates this?

Yes expoxidation is concerted

This is indicated by only seeing cis- (meso) configuration or only seeing trans- configurations, not both, in products

(* cis or trans depends on E or Z starting configuration)

Essentially the concerted mechanism "locks" the original configuration in place

23

E configuration alkene products of expoxidation

2 Trans enantiomers

24

Z configuration alkene products of expoxidation

1 meso cis- configuration

25

Regiochemistry of expoxidation in base

Base will attack the less substituted side of the intermediate since it attacks in a SN2-like nature

26

Regiochemistry of expoxidation in acid

Acid will create a cation intermediate

This positive charge will allow the nucleophile to attack the more substituted (and more positive) carbon

27

Configurational diastereomers

can only happen with 2 or more asymmetric carbons

configurations are not the same or mirror images

ex: RS and RR or E and Z

28

Configurational enantiomers

can happen with only 1 or more asymmetric carbons

carbons that are completely symmetric

ex: RRR to SSS

29

Example of Conformational enantiomers

rotating around a sigma bond to make gauche on the other-side

30

Meso compound checklist

1. Has at least 2 stereocenters
2. There is an internal mirror plane
3. Ensure tht each half is infact a mirror image by doing R/S
4. Each stereocenter must have the same connectivity