Neil Keddie- Lecture 4 Nucleophilic Substitution 3 Flashcards
What makes a good leaving group?
It must be stable enough to use and reactive enough when required.
What affects the choice of leaving group?
The C-X bond strength
The stability of the X- ion
How is anion stability estimated?
The pKa of the corresponding conjugate acid
A good leaving group is….
The conjugate base of a strong acid
What must happen to hydroxide to act as a leaving group?
Protonation by a strong acid
Conversion into a sulphonate ester (in the presence of a base) this is an SN2 reaction
Rank the sulphonate esters reactivity.
Tosylate (R-OTs)
Mesylate (R-OMs)
Triflate (R-OTf)
How are alcohols converted to alkyl chlorides?
Reaction with thionyl chloride (SOCl2)
(this is a sequential SN2 reaction first at sulphur then at carbon)
How does the conversion of alcohol to alkyl chloride affect stereochemistry?
1st substitution has no effect as occurs at sulphur
2nd causes stereochemical inversion
How can an ether be made reactive?
Protonation
What are epoxides?
Cyclic ethers that reaction without further activation due to ring strain (60°<120°)
What is regioselectivity?
When the structure of a product is determined by the hindrance of the reactant due to its shape.
Where does SN2 substitution causing ring opening occur on a epoxide?
The least sterically hindered end
