Chp 5—Stereochemistry

Question 1

of stereoisomers =

Answer 1

2^n, if n = chiral centers in molecule

Question 2

(+) rotation of light

Answer 2

dextrorotary

Question 3

(-) rotation of light

Answer 3

levorotary

Question 4

atropisomers

Answer 4

conformational isomers that are stable, isolable compounds - bond rotation is restricted by sterics (large molecules) or double/triple bonds

Question 5

internal racemic mixture

Answer 5

meso

Question 6

separation of enantiomers

Answer 6

resolution

Question 7

chemical resolution

Answer 7

racemic mixture reacts with pure enantiomer of a compound - forms diastereomers

Question 8

kinetic resolution
downside

Answer 8

one enantiomer reacts quickly, the other slowly
May use enzymes specific to one enantiomer
Lose ½ of compound to reactions

Question 9

chromatographic resolution

Answer 9

use chiral column - enantiomers form bands based on how tightly they are bound to column

Question 10

highest tech resolution

Answer 10

chiral HPLC

Question 11

solvent

water

Answer 11

PP

Question 12

solvent

Acetic acid

Answer 12

PP

Question 13

solvent

Acetone

Answer 13

PP

Question 14

solvent

Acetonitrile

Answer 14

PA

Question 15

solvent

DCM

Answer 15

PA

Question 16

solvent

DMSO

Answer 16

PA

Question 17

solvent

DMF

Answer 17

PA

Question 18

solvent

tetrachloromethane

Answer 18

PA

Question 19

solvent

Tetrahydrofuran

Answer 19

PA

Question 20

walden inversion

Answer 20

Nu attacks substrate at 180° from LG - configuration of groups on stereoatom invert 100%

Question 21

provides alcohol group for Sn2

Answer 21

NaOH

Question 22

provides ether for Sn2

Answer 22

NaOR

Question 23

provides thiol for Sn2

Answer 23

NaSH

Question 24

provides thioether for Sn2

Answer 24

NaSR

Question 25

provides nitrile for SN2

Answer 25

CN-

Question 26

provides ether for Sn2

Answer 26

RCOOH

Question 27

GOOD Nu for Sn2

Answer 27

• negative
• sterically unhindered/linear
• strong bases
• low EN
• large and polarizable

Question 28

Sn2 favored by ____ solvents

Answer 28

PA

Question 29

why does a PA solvent favor SN2?

Answer 29

the (-) part of solvent surrounds the (+) counterion on Nu, leaving Nu “naked”

Question 30

crown ethers used for…

Answer 30

Sn2

Question 31

GOOD LG for Sn2

Answer 31

• greater EN than C
• leaves as a stable weak base
• become neutral upon leaving

Question 32

substrates favored by Sn2

Answer 32

methyl, 1°

Question 33

substrates favored by Sn1

Answer 33

benzyl, allyl, 3°

Question 34

rds in Sn1

Answer 34

step 1 - LG leaving

Question 35

Hammond-Leffler postulate

Answer 35

TS structure resembles stable species closest in energy profile to the TS

Question 36

3 factors affecting CC+ stability

Answer 36

• resonance
• inductive effects
• hyperconjugation

Question 37

GOOD LG for Sn1

Answer 37

• larger LG
• weaker bases after departure

Question 38

Sn1 favored by ____ solvents

Answer 38

PP

Question 39

Why do PP solvents favor Sn1?

Answer 39

H+ solvates (-) halide after breakage of bond; carbocation is solvated by the (-) pole of the solvent

Question 40

solvolysis

Answer 40

Nu is a molecule of the solvent

Question 41

what most effects whether Sn1 will occur and how fast?

Answer 41

CC+ stability