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Organic chemistry > Exam 3 > Flashcards

Exam 3 Flashcards

1
Q

addition

A

A+B=C

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2
Q

elimination

A

A=B+C

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3
Q

substitution

A

A+B=C+D

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4
Q

rearrangement

A

A=B

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5
Q

homolytically

A

one bonding electron stays with each half of the molecule
radical reaction

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6
Q

heterolytically

A

two bonding electrons stay with one half of the molecule
polar reaction

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7
Q

radical reaction

A
  1. initiation: radical formation
  2. propagation: radical reacts with another molecule, radicals formed continue on in the reaction
  3. termination: two radicals recombine
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8
Q

polar reaction

A

heterolytic bond cleavage of polar compounds
addition, elimination, substitution, rearrangement

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9
Q

naming priority

A
  1. alcohol
  2. alkenes
  3. halide/alkyl
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10
Q

alkene stereochemistry

A

no rotation around double bond
2 possible stereoisomers of 1,2-disubstituted alkenes: cis and trans

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11
Q

Z and E

A

rank the 2 groups directly bound to each C of the alkene according to atomic #
Z: two high priority groups on same side
E: two high priority groups on opposite sides
Z and E are stereoisomers (diastereomers)
(R and S are enantiomers)

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12
Q

-diene

A

suffix for two double bonds

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13
Q

alkene stability

A

increase with substitution
hyperconjugation
trans is more stable

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14
Q

alkenes in cycloalkanes

A

more stable as cis
only rings of 8+ can have trans alkenes
alkenes in cyclohexanes adopt half chair conformation

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15
Q

intermediate

A

energy minimum

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16
Q

transition state

A

energy maximum

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17
Q

activation energy

A

higher energy/hump = slower reaction = rate limiting

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18
Q

alcohol

A

require initial protonation to activate alcohol and make it a good LG
can be protonated by HX or H+ when NaX is used

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19
Q

SN1 of alcohol

A

higher substitution
inversion of stereochemistry: due to association of carbocation with H2O LG, alcohol blocks and nu attacks from face opposite H2O
1. protonation
2. LG leaves
3. nu attack of carbocation

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20
Q

SN2 of alcohol

A

low substitution
no stereochemistry
1. protonation
2. nu attach

21
Q

thionyl chloride SOCl2

A

amine acts as a base and catalyst

22
Q

phosphorus trichloride/tribromide (PX3)

A

Cl or Br replaces OH

23
Q

sulfonates (OMs and OTs)

A

sulfonates are SO2R groups
weak base to prepare alkyl sulfonates from alcohols
TsCl and pyridine to turn OH to OTs, inversion of stereochemistry

24
Q

carbocation

A

positively charged carbon
stability increases with substitution (hyperconjugation)
empty p-orbital, stable when filled with adjacent C

25
Q

elementary reactions of carbocations

A

formation: loss of LG
sp2 planar, nu can attack from either side -> mix
loss of H+ -> alkene

26
Q

hyperconjugation

A

share electron density from C-H bond into empty p-orbital

27
Q

hydride shift (H-)

A

one position over to increase substitution

28
Q

alkyl shift

A

one position over to increase substitution
harder, will only happen if no adjacent hydride

29
Q

leaving group

A

ability to stabilize negative charge
Ex: Cl, Br, I, OTs, OMs, OR2+
required by SN1 and E2

30
Q

electrophile

A

site of low electron density
pos charge, resonance that makes pos charge, polarization away from carbon
c with LG must be sp3

31
Q

effect of substitution

A

increases, reaction favors SN1 bc more stable carbocation intermediate and carbon is less accessible to nu
accelerates both E1 and E2 bc more stable carbocation for E1 and more stable alkene for E2

32
Q

nucleophile

A

site of high electron density
negative charge, pi bond, polarized toward carbon, lone pair
strong nu required for SN2
stronger for anionic and down a column
strong base is usually a strong nu

33
Q

base

A

E2 requires a strong base, E1 favors weak base

34
Q

poor base, poor nu

A

H2O, H3O+, EtNH2
E1 and SN1

35
Q

strong base, poor nu

A

tBuO-
E2

36
Q

poor base, strong nu

A

X-
N triple C-
RS-
RSH-
SN2

37
Q

strong base, strong nu

A

HO-
CH3O-
EtO-
H2N-
E2

38
Q

protic

A

ability to donate H+
stabilizes nu/base and cationic intermediates and transition states -> SN1 and E1
aprotic -> SN2 and E2, fastest

39
Q

polar solvent

A

have a dipole moment
SN1 rate increases, little effect on SN2 rate

40
Q

bimolecular

A

two molecules in rate limiting step
single step
rate affected by both concentration

41
Q

unimolecular

A

one molecule in rate limiting step
nu/base has no effect on rate
higher energy step is rate limiting

42
Q

SN1 of alkyl halides

A

unimolecular
LG leaves first
sp2 planar carbocation intermediation, nu attacks from either side, racemic mixture
carbocation can rearrange before step 2
good LG, 2, 3, polar protic, weak nu/base

43
Q

SN2 of alkyl halides

A

bimolecular
backside nu attack, inversion of stereochemistry
partial bonds in transition state
me, 1, strong nu, aprotic

44
Q

E1 of alkyl halides

A

unimolecular
regioselectivity: form more substituted alkene product (constitutional isomers)
stereochemistry: form more stable alkene product (stereoisomers)
good LG, weak nu/base, 2, 3, protic
one product

45
Q

E2 of alkyl halides

A

bimolecular
require antiperiplanar geometry: H-C-C-LG lies in same plane with H and LG anti
results in single stereoisomer product
zaitsev’s rule
1 if bulky base, 2/3 if strong base, aprotic

46
Q

zaitsev’s rule

A

if two different beta H
more substituted/internal alkene product will form
less substituted product can form with bulky base: tert-butoxide

47
Q

HX and alcohol

A

SN2: Me, 1
SN1: 2, 3

48
Q

strong acid and alcohol

A

E2: 1
E1: 2,3

Organic chemistry (6 decks)

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