Nucleophilic substitution: SN1
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What are the basic steps of an SN1 reaction?
Leaving groups departs, leaving the carbenium ion which is attacked by Nu-
Which step is the rate determining step?
The slowest step
Is the rate determining step reversible or irreversible?
Reversible
Why is the fastest step irreversible?
There is electrostatic attraction between the negative nucleophile and the positive carbenium ion
What is hyperconjugation?
Electrons from the sp3 hydrogen are donated into the empty p orbital in the same plane
What is more effective hyperconjugation or pi conjugation
Pi conjugation
What does S stand for?
Substitution
What does N stand for?
Nucleophilic
What does the 1 stand for?
Unimolecular
What does unimolecular mean?
Only one molecule involved in the rate determining step
What do the graphs for rate kinetics show?
If you change one molecule and keep the other constant, the rate increases If you change the other while you keep the other constant, the rate stays the same Shows only one is involved in RDS
How many transition states are there for SN1 kinetics diagram?
two
What are the transition states?
R—X Nuc —- R
Which transition state is higher in energy?
R—-X
Which activation energy is the highest?
The one which causes the loss of the leaving group meaning that one is determining
What are the two axes for a reaction diagram?
Energy on Y (With a scale) Reaction co-ordinate on X
What are the two SN1 substrate effects?
Stability of the carbenium ion intermediate Leaving group ability of X-
How does the stability of the carbenium ion intermediate effect?
The stability of the first transition state determines the rate of reaction, partially positive charge on the carbon atom is stabilised
What is able to stabilise a carbenium intermediate?
Any electron donating group attached to the electron deficient carbon
What are the most to least stable carbenium ions?
Tertiary Secondary Primary Methyl
How do alkyl groups help to stabilise the carbenium ion?
They are electron donating
How does hyperconjugation stabilise the carbenium ion?
The alkyl groups stabilise the carbenium ion by donating electrons from pi bonds when overlapped with the p orbital
Which type of conjugation is more effective at stabilising carbenium ions; pi or hyper?
Pi conjugation
What does pi conjugation result in?
A positive carbenium ion where the positive charge is spread across two or more atoms