SN2 reactions

Question 1

concerted reaction

Answer 1

everything happens at the same time/same step

Question 2

stereospecific reaction

Answer 2

stereochemistry of product is based on stereochemistry of reactant
- based on LUMO of electrophile and HOMO of nucleophile

Question 3

how are SN2 reactions stereospecific?

Answer 3

• electrons from HOMO of nucleophile added to sigma antibonding MO of electrophile, which breaks bond to LG
• back-side attack: nucleophile comes from behind to attach electrophile LG

Question 4

factors in SN2 reactions

Answer 4

• electrophile: should be less sterically hindered and have a good LG
• nucleophile: should be a strong nucleophile, not just a strong base
• solvent: must dissolve nucleophile but not hold on so tightly that reaction slows down

Question 5

how does steric hindrance affect SN2 reaction?

Answer 5

• CH3 groups next to alpha carbon make it hard to attack electrophile; 3 CH3 groups does not react
• CH3 groups on beta carbon can also cause hindrance

Question 6

good leaving groups

Answer 6

• usually halides, sulfonates, or other resonance stabilized anions!

Question 7

nucleophilicty vs basicity

Answer 7

• most of the same rules apply
• strong bases can donate e- more easily, strong nucleophiles can donate them faster
• larger atoms are most stable bases (less e- repulsions) but stronger nucleophiles (e- further from + nucleus)

Question 8

solvents for SN2 reaction

Answer 8

• should be polar (but not too polat) and often aprotic