SN2 reaction & SN1

Question 1

SN2 reactions

Answer 1

Nucleophile approaches electrophile from the opposite side of the molecule to the leaving group

Question 2

Transition state

Answer 2

• Theoretical representation of the high energy point between starting materials and products. It does not physically exist

Question 3

Why SN2

Answer 3

Reaction occurs in one step, with no intermediates formation

Question 4

Bimolecular reactions

Answer 4

Two species are involved in the rate determining step defined as the slowest step of a reaction

Question 5

What is involved in rate limiting step

Answer 5

• Electrophile and nuclephile

Question 6

Transition state

Answer 6

• Bond to the nucleophile (hydroxide) is partially formed, and the bond to the leaving group (bromide) is partially broken

Question 7

SN2 on Alkyl Halide

Answer 7

• Nucleophiles convert alkyl halides to a wide variety of functional groups

Question 8

Omeprazole

Answer 8

Proton pump inhibitor that decreases the amount of acid produced in the stomach

Question 9

Factors Affecting SN2 reaction

Answer 9

• Strong nucleophile reacts faster in SN2 reaction
• Species with negative charge
• Base has a stronger nucleophile than its conjugate acid

Question 10

Basicity

Answer 10

Equilibrium constant for abstracting an acidic proton forms a new bond to a proton, it has reacted as a base

Question 11

Nucleophilicity

Answer 11

Rate of attack on an electrophilic carbon atom forms a new bond to carbon, it has reacted as a nucleophile

Question 12

Trend of Nucleophilicity

Answer 12

• Decreases from left to right in the periodic table, following the increase in electronegativity
• tightly held non-bonding electrons that
  are less reactive toward forming new bonds
• Increases down the periodic table, following the increase in size and polarizability

Question 13

An increase in nucleophilicity

Answer 13

• More loosely held, can move more freely toward a positive charge, resulting in stronger bonding, enhancing the atom’s ability to begin to
  form a bond at a relatively long distance

Question 14

Nucleophile

Answer 14

• An ion or a molecule must get close to a carbon atom to attack it
• Bulky groups on the nucleophile hinder this close approach, slow the reaction rate

Question 15

Steric hinderance

Answer 15

• Slower SN2 reaction in larger molecules e.g stronger base means weaker nucleophile
• Weaker base means stronger nucleophile

Question 16

Solvent effect on Nucleophilicity

Protic solvent

Answer 16

• OH/NH groups H bonds to negatively charged nucleophiles very good in solublising reduce nucleophilicity small anion
• Not good for SN2 reaction

Question 17

Aprotic solvent

Answer 17

• Without OH/NH enhances nucleophilicity
• Anions are more reactive with weak solvating

Question 18

Polar aprotic solvent

Answer 18

• OH or NH enhances solubility
• Enhances SN2 REACTION SOLUBLISE WITH REAGENT AND DOESNT FORM HYDROGEN BOND

Question 19

Polar aprotic solvent

Answer 19

• OH or NH enhances solubility
• Enhances SN2 REACTION SOLUBLISE WITH REAGENT AND DOESNT FORM HYDROGEN BOND

Question 20

Electron withdrawing

Answer 20

• Polarise the carbon atom stablise the negatively charged transition state, Halogen, oxygen, nitrogen and sulpher
• Stable once left weak base conjugate strong acid
• Strong base poor leaving group OH
• +NMe3 > TsO— > I— > Br — > +OH2 > Cl— > F— > OH- order of leaving group strength

Question 21

Sn2 reaction with electron deficient molecule

Answer 21

electron deficient (positive) nitrogen gains a pair of electrons from the broken bond, forming a stable
neutral molecule

Question 22

Factors that effect Sn2 reaction methyl groups

Answer 22

• Steric bulk of the electrophile influences the mechanism of the reaction
• 3 methyl groups mean that there is more steric hinderance less acess to carbon

Question 23

Inversion of configuration

Answer 23

• When the electrophile attacks from the backside it causes the conversion srom S to R visa versa

Question 24

Why are SN2 reactions important

Answer 24

Avoid side-effects from unwanted isomers you recommend to a drug development researchers that only the RR isomer of Labetalol should be available

Question 25

Sn1 reaction rate

Answer 25

- Doesn't depend on conc of nucleophile but depends on conc of the electrophile - Substitution nucleophilic unimolecular reaction

Question 25

Sn1 reaction rate

Answer 25

- Doesn't depend on conc of nucleophile but depends on conc of the electrophile - Substitution nucleophilic unimolecular reaction

Question 26

Unimolecular reaction

Answer 26

- Only one specie is involved in the rate determining step

Question 27

Substituent effect

Answer 27

- The EASIER the formation of the carbocation intermediate, the faster the SN1 - The MORE STABLE the carbocation, the faster the SN1 more donation the electrons to the central positive

Question 28

Sn2 ease of reaction

Answer 28

- Lots of electron density +ve charge stabilised - Low electron density +ve charge poorly stabilised - Tertiary is fast and primary is not possible

Question 29

Steps of Sn1 reaction

Answer 29

- Formation of carbon cation - Nucleophilic attack on the carbocation - Loss of proton to solvent

Question 30

Racemisation reaction

Answer 30

- 50% of S and 50% of R - Attacted by 2 sides mixture around the chiral carbon

Question 31

Resonance stabilisation

Answer 31

- Carbon cation promotes the Sn1 reaction - Leaving groups effect - weak base vaey stable after it leaves with pair of electrons bonded to carbon -

Question 32

Protic solvents

Answer 32

- Polar solvents stabilise ions, therefore favour SN1. H2O, alcohols

Question 33

Methyl shift can occour

Answer 33

- More stablised as tertiary carboncation is more stable