CH10: Elimination Reactions Flashcards
What is the alpha-carbon of an elimination mechanism?
The carbon in which the LG is attached to.
What is the beta-carbon of an elimination mechanism?
The carbon(s) next door to the alpha-carbon / directly bonded together.
What is the Beta-Hydrogen?
A hydrogen that is connected to a beta-carbon.
What is the biggest difference between E2 and SN2 as it relates to substrates? Why is it possible?
An E2 can occur at 3* whereas an SN2 cannot.
This is because E2 is just taking a hydrogen, whereas SN2 is trying to enter through the back of the substrate.
Define regiochemistry
Where the reaction takes place on a molecule.
With multiple options for Beta-Hydrogen removal, how do you know which product will form/is favored?
Due to Zaitsev and Hofmann.
What is Zaitsev and Hofmann?
Zaitsev is the more substituted alkene. Typically more stable and the major product. (favored!)
Hofmann is the less substituted alkene. Minor product.
How do you determine how substituted an alkene is?
The more R-groups around the alkene
(mono, di, tri, and tetra)
What 2 reagents automatically make it an elimination reaction?
tBuOK (Potassium tert-butoxide)
LOA (Lithium Di-isopropyl Amine)
What relationship is needed between the Beta-Hydrogen and L.G?
An antiperiplanar relationship
Define antiperiplanar
Opposite configuration (wedge LG wants dash Beta-Hydrogen and vice versa)
How do single bonds rotate? Can they rotate in a ring?
plane -> dash -> wedge
NO cannot rotate in ring.
What type of products will you get when dealing with carbocations?
Will typically get a mix of E1 and SN1
What are the exceptions to the mixture of E1 and SN1?
H2SO4 as nuc/base
Heat
These make it E1 reaction ONLY
Does E1 need an antiperiplanar relationship?
No. Carbocations are flat so there is no stereochemistry.
