SN2

Question 1

What are the requirements for an SN2 reaction?

Answer 1

1. Reagent/Electrophile
2. Nucleophile/Lewis base
3. Reaction Conditions: solvent, temp., and time

Question 2

What must the reagent/substrate/electrophile in an SN2 reaction have?

Answer 2

-must have a good leaving group (LG)
-must be sp3 hybridized
-must minimize steric hindrance

Question 3

What is a leaving group?

Answer 3

Weak base/stable anion; conj. base of strong acid that can handle lone pairs

Question 4

Why must the electrophile minimize steric hindrance?

Answer 4

Steric hindrance slows SN2 reactions because it lowers the energy of the transition state

Question 5

What are the properties of Alkyl Halides?

Answer 5

1. Bond strength of C–X decreases as the size of X increases (unfavorable orbital overlap)
2. Bond length of C–X increases as the size of X increases (bond strength decreases, so bond lengthens)
3. C–X bond is polarized (eneg, carbon is electrophile)

Question 6

What is the easiest way to classify types of Alkyl Halides (i.e. primary, secondary, tertiary, etc.)?

Answer 6

Look at how many CARBONS are connected to the C–X bond; this classification only applies to sp3 carbons

Question 7

What are the two options for nucleophilic substitution?

Answer 7

1. Concerted process (SN2)
2. Stepwise process (SN1)

Question 8

Describe SN2 reactions.

Answer 8

-one step process
-need a strong nucleophile
-need a good electrophile

Question 9

Describe SN1 reactions.

Answer 9

-multi-step mechanism
-weak nucleophile
-awesome electrophile

Question 10

All SN2 reactions proceed with …

Answer 10

inversion of configuration

Question 11

What are the two options for an SN2 transition state? Which is better?

Answer 11

1. frontside attack (bad)
2. backside attack (better)

Question 12

Why is a frontside attack bad?

Answer 12

-electronic repulsion; 2 negative dipoles in the same space from nucleophile and LG repel each other
-steric hindrance; nuc and LG are trying to occupy the same space
-retention of configuration results; not possible in SN2

Question 13

Why is backside attack better?

Answer 13

-180 degree alignment of nucleophile and LG relieves steric and and electronic issues
-better orbital orientation (attacks anti bonding orbital)
-results in inversion of config, called an umbrella flip

Question 14

What results in the overall retention of configuration?

Answer 14

Double inversion

Question 15

Why are intramolecular reactions faster than intermolecular reactions?

Answer 15

Nuc and electrophile are in the same molecule instead of two separate molecules

Question 16

What should we ask ourselves when trying to determine what a good substrate for SN2 would be?

Answer 16

What does the LG become after it leaves? Stable? Other substrate properties? (Try and mock the SN2 mechanism)

Question 17

Nitrogens are _______ when they are sp3 hybridized.

Answer 17

Strong nucleophiles

Question 18

In an endothermic TS, the bonds forming _____ are short.

Answer 18

Products

Question 19

In an exothermic TS, the bonds forming _____ are short.

Answer 19

Reactants