Chp 5—Stereochemistry Flashcards

1
Q

of stereoisomers =

A

2^n, if n = chiral centers in molecule

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2
Q

(+) rotation of light

A

dextrorotary

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3
Q

(-) rotation of light

A

levorotary

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4
Q

atropisomers

A

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

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5
Q

internal racemic mixture

A

meso

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6
Q

separation of enantiomers

A

resolution

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7
Q

chemical resolution

A

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

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8
Q

kinetic resolution
downside

A

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

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9
Q

chromatographic resolution

A

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

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10
Q

highest tech resolution

A

chiral HPLC

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11
Q

solvent

water

A

PP

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12
Q

solvent

Acetic acid

A

PP

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13
Q

solvent

Acetone

A

PP

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14
Q

solvent

Acetonitrile

A

PA

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15
Q

solvent

DCM

A

PA

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16
Q

solvent

DMSO

A

PA

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17
Q

solvent

DMF

18
Q

solvent

tetrachloromethane

19
Q

solvent

Tetrahydrofuran

20
Q

walden inversion

A

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

21
Q

provides alcohol group for Sn2

22
Q

provides ether for Sn2

23
Q

provides thiol for Sn2

24
Q

provides thioether for Sn2

25
provides nitrile for SN2
CN-
26
provides ether for Sn2
RCOOH
27
GOOD Nu for Sn2
- negative - sterically unhindered/linear - strong bases - low EN - large and polarizable
28
Sn2 favored by ____ solvents
PA
29
why does a PA solvent favor SN2?
the (-) part of solvent surrounds the (+) counterion on Nu, leaving Nu “naked”
30
crown ethers used for...
Sn2
31
GOOD LG for Sn2
- greater EN than C - leaves as a stable weak base - become neutral upon leaving
32
substrates favored by Sn2
methyl, 1°
33
substrates favored by Sn1
benzyl, allyl, 3°
34
rds in Sn1
step 1 - LG leaving
35
Hammond-Leffler postulate
TS structure resembles stable species closest in energy profile to the TS
36
3 factors affecting CC+ stability
- resonance - inductive effects - hyperconjugation
37
GOOD LG for Sn1
- larger LG - weaker bases after departure
38
Sn1 favored by ____ solvents
PP
39
Why do PP solvents favor Sn1?
H+ solvates (-) halide after breakage of bond; carbocation is solvated by the (-) pole of the solvent
40
solvolysis
Nu is a molecule of the solvent
41
what most effects whether Sn1 will occur and how fast?
CC+ stability