Alkenes Flashcards
How can you make an alkene from an alkyne
1) Lindlars catalyst and H2
2) NH3/ Na
3) H2 and pt goes all the way to alkane
What sort of addition is lindlars
Syn
What sort of addition is NH3 (low) / Na
Radical mechanism
Anti
Define stereoselective
The reaction pathway has a choice
Describe an E1 mechanism
2 steps
Dilute tertiary
Stereoselective
Eclipsed conformer is fastest reaction as steric strain is removed
Why is E1 stereoselective
The carbon bond can rotate freely
Describe an E2 mechanism
1 step
Favours primary and concentrated
Stereospecific
Favours staggered
Why is E2 stereospecific
The elimination can only proceed via anti periplanar conformation
Define regioselectivity
The reaction has a choice of products but one is favoured over the other
Is E1 regio selective or specific
Regioselective - the Saytzeff rule states that the most highly substituted Alkene is formed
Is E2 regio selective or specific
Regioselective - follows saytzeff unless a large bulky base is used then it follows Hofmann - least sub alkene favoured
What is a large bulky base
Potassium tert butoxide
In a cyclic ring elimination what conformer is required
1,3 diaxial
How can you make an alkene from an alcohol
Acid catalyst
What are elimination reactions in competition with
Sub because the base can act as a nucleophile
What does the Wittig reaction use
Aldehyde or ketone and phosphorane
What is the Wittig reactions selectivity and specificity
Regiospesific and stereoselective
How can you produce phosphorane
PPH3 + CH3Br -> salt BuLi
Or
Alpha halo Ester and NaOH
What determines the stereoselectivity of Wittig
Electron withdrawing gives E
What does the Julia Olefination use
Phenylsulfone and ketone
Acetic anhydride
Na/Hg
What is the specificity and selectivity of the Julia reaction
Regiospesific and stereoselective
What does the Peterson reaction use
Silylcarbanions
What is produced under acidic conditions in the Peterson.
Trans alkene
What is produced under basic in Peterson
Cis
