Alkenes + Alkynes Flashcards
What does dehydration of ROH lead to
Double bonds
What is the alpha carbon
What about beta
First Carbon attached to the functional group
Beta is the carbon next to the alpha carbon
What are common H+ catalysts
H2SO4, H3PO4, KHSO4
Under acidic conditions what type of catalyst do you want
Under basic?
Want cations or neutral
Want anions or neutral
When doing dehydration reactions (remove oh and make double bond) what are the conditions needed for primary to tertiary ROH
Primary neeeds higher temp/nrg, has higher transition state
Going to tertiary you need lower temp/nrg, lower transition state
When does Zaitsevs rule happen?
What type of reaction is it
When you have inequivalent beta carbon, have to choose where double bond goes
Regioselective reaction
What is sterioselectivity
Antizaitsev product can give either cos or trans isomer
What is regiospecific
Want more electron donating (methyl groups) in the product
Results in only one product
Beta elimination reactions of ROH’s use what and give what as the product
Use H2SO4 of remove OH and make double bond
Give most highly substituted Alkene as the product and can make cos and trans isomers of the product
What products are more stable in beta elimination reaction
The trans (E) Isomer
What compunds are good for alcohol dehydration
(E2)
H3PO4
H2SO4
KHSO4
Where are 1,2 hydride shifts common
In primary roh (oh on primary carbon)
Concerted (E2)
F is a ___
Bad LG
What are examples of small bases
What do they give
NaOme
KOH
EtOH
Zairsev product
If you have a primary alkyl halide and want a terminal Alkene (want antizaitsev) what do you use
Ktbu/heat and DMSO
bulky base, aprotic solvent
Electron donating groups do what to a double bond
Stabilize it, this is why zaitsev is best
Do hydride shifts occur under basic conditions
No
Is ring systems where cos and trans is possible, which conformation about the double bond it better
Cis because less steric hindrance
(Slide 16)
What is a double dehydrohalogenation
Two halogens on compound, removing both to make a triple bond
What is a geminal dihalide
What is vicinal dihalide
The halogens cl,br,I are connected to the same carbon
The halogens are connected to different carbons
What do you need to go from a geminal dihalide to an alkyne
- 3 equiv of NaNH2, in liq. NH3
- H2O
Why is the pka of a terminal alkyne lower (25)
The s charcter is increased so if h was taken of of it the anion would be stabilized since it’s close to the nucleus
It would be deprotonated in geminal di halide reactions
Then become excellent nucleophile
What is the basic concept in addition reactions
Have Nu—E with c=c. Then double bond is gone and NU and E are added
What is the basic steps in addition reactions
- Transformation
- Regiochemistry
- Stereochemistry
