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CH341—Organic Chemistry I > Chp 5—Stereochemistry > Flashcards

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

A

PA

18
Q

solvent

tetrachloromethane

A

PA

19
Q

solvent

Tetrahydrofuran

A

PA

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

A

NaOH

22
Q

provides ether for Sn2

A

NaOR

23
Q

provides thiol for Sn2

A

NaSH

24
Q

provides thioether for Sn2

A

NaSR

25
Q

provides nitrile for SN2

A

CN-

26
Q

provides ether for Sn2

A

RCOOH

27
Q

GOOD Nu for Sn2

A
  • negative
  • sterically unhindered/linear
  • strong bases
  • low EN
  • large and polarizable
28
Q

Sn2 favored by ____ solvents

A

PA

29
Q

why does a PA solvent favor SN2?

A

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

30
Q

crown ethers used for…

A

Sn2

31
Q

GOOD LG for Sn2

A
  • greater EN than C
  • leaves as a stable weak base
  • become neutral upon leaving
32
Q

substrates favored by Sn2

A

methyl, 1°

33
Q

substrates favored by Sn1

A

benzyl, allyl, 3°

34
Q

rds in Sn1

A

step 1 - LG leaving

35
Q

Hammond-Leffler postulate

A

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

36
Q

3 factors affecting CC+ stability

A
  • resonance
  • inductive effects
  • hyperconjugation
37
Q

GOOD LG for Sn1

A
  • larger LG
  • weaker bases after departure
38
Q

Sn1 favored by ____ solvents

A

PP

39
Q

Why do PP solvents favor Sn1?

A

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

40
Q

solvolysis

A

Nu is a molecule of the solvent

41
Q

what most effects whether Sn1 will occur and how fast?

A

CC+ stability

CH341—Organic Chemistry I (9 decks)

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