Steroechemistry Mechanisms For Alkenes, Alkynes, And Diels Alder Reactions

Front 1

Alkene Reactions

Back 1

Front 2

Hydrohalogenation

Back 2

Reagents:

HX (X = Br, Cl, F, etc.) + alkene —> haloalkane

Mechanism notes:

1. Carbocation forms (most stable)

2. Nucleophile attacks carbocation

Regiochemistry: Markovnikov

Stereochemistry:

syn. and anti. products form

Extra notes:

- watch for C+ rearrangements

Front 3

Acid-catalyzed hydration or ether formation

Back 3

Reagents:

H2SO4 + H2O or R-OH + H2SO4

Regiochemistry: Markovnikov

Stereochemistry:

syn. and anti. products form

Extra notes:

1. H3O+ formation

2. Carbocation formation

3. Nucleophile attacks

4. Watch for C+ rearrangements

Front 4

Halogenation

Back 4

Reagents:

Br2 or Cl2 + DCM —> dihalide

Regiochemistry: Anti-markovnikov

Stereochemistry:

anti.

Extra notes:

- bromonium or chloronium intermediate (no C+)

- I2 and F2 don’t react!

Front 5

Hydroboration

Back 5

Reagents:

1. BH3/THF

2. H2O2, OH-, H2O

—> less substituted alcohol

Regiochemsitry: Anti-markovnikov

Stereochemistry:

syn.

Front 6

Halohydrin formation

Back 6

Reagents:

Br2 or Cl2 + H2O

—> halohydrin

Mechanism notes:

same mech. as Br2/DCM

Regiochemistry: pseudo-Markovnikov b/c OH adds to more substituted C of alkene

Stereochemistry:

anti.

Extra notes:

- also works with R-OH instead of H2O

Front 7

Expoxidation

Back 7

Reagents:

MCPBA (or any peroxyacid) —> epoxide

Regiochemistry:

n/a

Stereochemistry:

syn.

Front 8

Ozonolysis

Back 8

Reagents:

1. O3, -78°C

2. DMS

—> ketone or aldehyde

Mechanism notes:

- don't need to know mech.

Regiochemistry:

n/a

Stereochemistry:

n/a

Extra notes:

- every C=C —> C=O

Front 9

Hydrogenation

Back 9

Reagents:

H2 + Pd/C

—> alkane

Mechanism notes:

don't need to know mech.

Regiochemistry:

n/a

Stereochemistry:

syn.

Extra notes:

- Pd/C = catalyst (or in this case Pt - Platinum)

- don't forget about sterochemistry

Front 10

Alkyne Reactions

Back 10

Front 11

Hydrogenation (dissolving metal reduction)

Back 11

Reagents:

Na/NH3 (l), -78°C

—> trans alkene

Regiochemistry:

n/a

Stereochemistry:

n/a

Extra notes:

- trans alkene

- does not work on terminal alkynes

Front 12

Hydrogenation

Back 12

Reagents:

H2 + Lindlar's catalyst

alkyne —> cis alkene

Front 13

Acid-catalyzed hydration (internal alkyne)

Back 13

Reagents:

H2SO4 + H2O

(internal alkyne —> ketone)

Regiochemistry:

Markovnikov

Stereochemistry:

n/a

Extra notes:

- ketone product

- asymmetric internal alkynes —> 2 products

Front 14

Acid-catalyzed hydration (terminal alkyne)

Back 14

Reagents:

Hg2+, H2SO4, H2O (terminal alkyne —> ketone)

Regiochemistry:

Markonikov

Stereochemistry:

n/a

Extra notes:

- ketone product

Front 15

HX alkyne addition

Back 15

Reagents:

HX

alkyne —> haloalkene

Regiochemistry:

Markovnikov

Stereochemistry:

n/a

Extra notes:

- 1 eq - add to carbocation

- 2 eq - add to same carbon as first halogen

Front 16

Halogen addition

Back 16

Reagents:

Cl2 or Br2

Regiochemistry:

n/a

Stereochemistry:

anti.

Extra notes:

Cl2 or Br2

Front 17

Hydroboration oxidation

Back 17

Reagents:

1. 9-BBN, THF

2. H2O2, H2O, NaOH

Mechanism notes:

- don't need to know mech.

Regiochemistry:

Anti-markovnikov

Stereochemistry:

n/a

Extra notes:

- terminal alkyne —> aldehyde

- internal alkyne —> ketone

Front 18

Diene Reactions

Back 18

Front 19

1, 2 addition

Back 19

Reagents:

HX or H2SO4, H2O, conjugated (alternating double bonds) diene

Stereochemistry:

+ E if you make a new asymmetric center (sp3 w/4 different groups)

Extra notes:

- to find which carbon is #1 (where the H goes) compare end carbons of diene and make #1 the less substituted one

- if the two end carbons are equal make the carbon that leads to the more stable carbocation as #1

Front 20

1, 4 addition

Back 20

Reagents:

HX or H2SO4, H2O, conjugated (alternating double bonds) diene

Stereochemistry:

+ E if you make a new asymmetric center (sp3 w/4 different groups)

Extra notes:

- cold —> 1, 2

- hot —> most stable alkene (1, 2 or 1, 4)

Front 21

Diels-Alder

Back 21

Reagents:

diene + dienophile + ∆ (heat)

Stereochemistry:

- things on the dienophile with π e- are endo and down (on a dash)

- things on carbons 1 + 4 of diene that are out are also down (on a dash)

- "OUT-ENDO-CIS"

- whatever is out on diene is cis to whatever is endo on the dienophile

Extra notes:

- diene must be s-cis

- dienophile must be alkene or alkyne