Week 5/6

Question 1

Epoxides SN2

Answer 1

• Nu attack occurs on less hindered C

- inversion of stereochem at electrophilic C

Question 2

General rules for solvent effects (2)

Answer 2

1. increasing solvent polarity will decrease rxn rate if reactants are charged
2. increasing solvent polarity increases rxn rate if reactants are neutral (stabilizes charges forming in TS, destabilizes GS)

Question 3

SN1 Solvent/nucleophile preference

Answer 3

• polar protic solvents preferred
• ie. H2O, EtOH, etc
• poor nucleophile
• good LG (pKa conj. acid>8)

Question 4

SN2 solvent effects

Answer 4

• polar aprotic solvents preferred
• good nucleophile
• good LG (pKa conj. acid>8)

Question 5

Polar aprotic solvent examples

Answer 5

acetone
DMSO (dimethyl sulfide)
acetonitrile
THF (tetrahydrofuran)
diethyl ether
DMF (dimethyl formamide)

Question 6

Nucleophilicity

Answer 6

• Depends on solvation (solvent shell must be disrupted for rxn to occur)
• depends on electronegativity (more electronegative nucleophiles are less reactive)
• polarizability (more polarizable is better Nu)
• negative charge increases nucleophilicity
• stronger base=stronger Nu

Question 7

polarizability

Answer 7

decreases from left to right, and from bottom to top of PT (F least polarizable)

Question 8

Nucleophilicity solvent effects

Answer 8

polar protic solvents:
-best Nu- is most polarizable, is harder for H to stabilize the electroneg atom (with or w/o -ve charge) when atom is larger
polar aprotic solvents:
-the -ve charged Nu- not strongly solvated, nuclophilicity correlates with basicity (called reverse reactivity trend)