SN1+SN2 reactions

Question 1

What are the types of solvents?

Answer 1

*protic solvents
*aprotic solvents
*polar aprotic solvents

Question 2

What are protic solvents + how it affects nucleophilicity

Answer 2

Protic solvents: OH/NH groups (i.e. alcohols)
H-bonds to negatively charged nucleophiles
Very good in solubilising reagents
Reduce Nucleophilicity of small anions

Question 3

What are aprotic solvents + how it affects nucleophilicity

Answer 3

Aprotic solvents: without OH/NH groups
(i.e. hexane).
Enhance nucleophilicity of anions
Anions are more reactive
Relatively weak solvating ability

Question 4

What are polar aprotic solvents + how it affects nucleophilicity?

Answer 4

Polar aprotic solvents: no OH or NH
Enhance solubility
Acetonitrile, dimethylformamide (DMF),
acetone, and dimethyl sulfoxide (DMSO)
From alcohol to DMSO often enhances the
rate of an SN2 reaction
Reverse the nucleophilicity order (F->Cl-..)

Question 5

What is entailed in an SN2 reaction?

Answer 5

Reaction occurs in one step, with no intermediates formation

Nucleophile and electrophile: both involved in the rate-limiting step

SN2: Substitution Nucleophilic Bimolecular reaction
*transition state: new bond partially formed and old bond partially broken

Question 6

What affects SN2 nucleophilic sub?

Answer 6

*strength of nucleophile
(nucleophilicity decreases from left to right on periodic table, increases down)
+bigger the size of molecule = better as the electrons are more loosely held = react quicker
+bulkiness of molecule, more bulk - slower reaction (hindered)

Question 7

How do the different types of alkyl halide effect SN2 reaction?

Answer 7

methyl derivative - very fast
primary - fast
secondary - slow
tertiary - not possible

Question 8

What is entailed in an SN1 reaction?

Answer 8

Reaction-rate: does not depend on the concentration of the nucleophile but depends only on the concentration of the substrate (electrophile)

Nucleophile reacts after the slow step
SN1: Substitution Nucleophilic,
Unimolecular reaction only one species involved in rate determining step

Question 9

How do the different types of substituents affect rate/possibility of SN1 reaction?

Answer 9

*tertiary - fast SN1
*secondary - intermediate
*primary - SN1 not possible

Question 10

What factors affect SN1 reactions?

Answer 10

*resonance stabilisation of carbocation promotes SN1
*leaving group effects weak base—very stable after it leaves with the pair of electrons that bonded it to carbon
*protic solvents - polar solvents stabilise ions, favour SN1 alcohols