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OCHEM 335 > Quiz 4 > Flashcards

Quiz 4 Flashcards

1
Q

Do Friedel-Crafts rxns occur with meta directors?

A

F-C rxns are the slowest electrophilic aromatic substitution rxns and do not occur if the ring has a meta director (if the ring is moderately or strongly deactivated)

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2
Q

what are meta directors

A

a substituent that favors electrophilic attack meta to the substituent. Most meta directors are also deactivators

Electron withdrawing groups are deactivators and therefore act as meta directors

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3
Q

explain why F-C rxns can’t have certain substituents

A

the lone pair on the lewis basic group (-NH2, -NHR, or -NR2) forms a complex with a Lewis acid catalyst, which converts the substituent to a meta director and thus deactivates the ring.

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4
Q

how do you install a straight chain alkyl group on a benzene ring

A

reactants: benzene + R with carbonyl group (c double bonded to O and a halogen like Cl)
1. reacts with AlCl3 which removes Cl and attaches R and carbonyl group to benzene ring (carbonyl is in between R and benzene – very important)
2. that reacts with H2 and Pd/C to produce just the benzene ring with the R group attached.

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5
Q

what are the effects of the substituents on the reactivity of a benzene ring

A

LEAST REACTIVE: benzene with an electron withdrawing group: substituents decrease benzene’s nucleophilicity and destabilizes the carbocation intermediate

benzene with a hydrogen:

MOST REACTIVE: benzene with an electron donating group: substituents increase benzene’s nucleophilicity and stabilizes the carbocation intermediate.

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6
Q

electron withdrawing group

A

typically electronegative atoms or groups that pull electron density away from a molecule, making it more positive and less reactive. Examples include halogens (such as fluorine, chlorine, and bromine), nitro groups, and carbonyl groups.

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7
Q

electron donating group

A

usually electron-rich and can donate electron density to a molecule, making it more negative and more reactive. Examples include alkyl groups, phenyl groups, and amino groups.

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8
Q

what is inductive electron withdrawal

A

When an electronegative atom is present in a molecular structure, it can pull electron density towards itself, creating a dipole moment and withdrawing electrons from neighboring atoms. This leads to a partial positive charge on the atom where the electrons are being withdrawn. This effect can propagate through a chain of atoms in a molecule.

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9
Q

what is inductive electron donation

A

If there’s an atom with a lower electronegativity, it may donate electron density to its neighboring atoms. This results in a partial negative charge on the atom donating electrons. Again, this effect can extend through a chain of atoms.

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10
Q

explain resonance electron donation and withdrawal

A
  • a lone pair on an atom directly attached to the ring DONATES electrons by resonance. This applies to all atoms with an available lone pair.
  • an atom directly attached to the ring that is doubly or triply bonded to an electronegative atom withdraws electrons by resonance
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11
Q

for resonance electron donation, where does the charge occur

A

usually three structures move the negative charge around the ring (the charge is only on the ortho and para positions)

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12
Q

for resonance electron withdrawal, where does the charge occur

A

usually three structures move the positive charge around the ring (the charge is only on the ortho and para positions)

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13
Q

what are strongly activating substituents

A
  • N or O with a lone pair
  • all substituents donate electrons by resonance and withdraw electrons inductively
  • because substituents are activating, electron donation by resonance is more significant than inductive electron withdrawal
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14
Q

what is the rule about activating vs. deactivating substances

A

activating substances always beat deactivating substances no matter how weak / strong either of them are

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15
Q

explain moderately activating substituents

A
  • donate electrons by resonance and withdraw electrons inductively
  • the lone pair is in competition for where it wants to delocalize, since it is in between an R group (usually with a carbonyl) and the benzene ring. So the two groups end up playing a tug of war with the lone pair.
    - the amount donated to the ring is less with the carbonyl present.
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16
Q

which are more effective, strongly or moderately activating substances?

A

moderately activating substituents are less effective than strongly activating substituents because they donate electrons in two competing directions

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17
Q

explain weakly activating substituents (alkyl vs. halogen)

A
  • alkyl substituents donate electrons inductively. weakly activating substituents (ex. aryl and CH=CHR) donate and withdraw electrons by resonance.
  • all the weakly deactivating substituents (halogens) donate electrons by resonance and withdraw electrons inductively
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18
Q

in the competition between inductive withdrawal and resonance electron donation, what wins?

A

inductive withdrawal wins but both donation and withdrawal still happen

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19
Q

explain strongly deactivating substituents

A
  • all the strongly deactivating substituents (except ammonium ions) withdraw electrons inductively and by resonance
  • ammonium ions strongly withdraw electrons inductively
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20
Q

list strongly activating groups

A
  • NH2
    -NHR
    -NR2
    -OH
    -OR
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21
Q

list moderately activating groups

A

-NHC(double bonded to O)R
-OC(double bonded to O)R

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22
Q

list weakly activating groups

A

-R
-Ar
-CH=CHR

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23
Q

list weakly deactivating groups

A

-F
-Cl
-Br
-I

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24
Q

list moderately deactivating groups

A

-C(double bonded to O)H
-C(double bonded to O)R
-C(double bonded to O)OR
-C(double bonded to O)OH
-C(double bonded to O)Cl

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25
Q

list strongly deactivating groups

A

-C triple bonded to N
-SO3H
-N+H2R
-N+R3
-NO2

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26
Q

which substituents direct where

A
  • strongly activating, moderately activating, weakly activating, and weakly deactivating –> ortho / para directing
  • moderately deactivating and strongly deactivating –> meta directing
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27
Q

what is the substituent orientation effect

A

EAS rxns always produce a mixture of all three products BUT, for simplicity:
- meta directors give only meta-substituted products
- ortho / para directors give only ortho / para-substituted products

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28
Q

what is a general rule about meta directors

A

all moderately and strongly deactivating substituents are meta director

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29
Q

what is a general rule about ortho / para directors

A
  • any substituent with a lone pair is an ortho / para director
  • all activating substituents are ortho / para directors
  • weakly deactivating substituents (halogens) are ortho / para directors
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30
Q

describe the sterics on the ortho / para ratio

A
  • in EAS, you always get a mixture of ortho and para products that you must separate
  • BIGGER GROUPS inhibit ortho and favor para (sterics)
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31
Q

what is an alternative way to predict whether a substituent directs ortho / para versus meta (based on the donation of electrons by resonance into a benzene ring)

A

resonance structures show that the ortho and para positions have more electron density than a normal benzene. Because of this increased electron density, an electrophile preferentially reacts at the ortho / para positions
- there is more electron density where the electrophile wants
to add

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32
Q

what is an alternative way to predict whether a substituent directs ortho / para versus meta (based on the withdrawal of electrons by resonance into a benzene ring)

A

resonance structures show that the ortho and para positions have less electron density than a normal benzene. because of this decreased electron density, an electrophile preferentially reacts at the meta position

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33
Q

what needs to be considered for the synthesis of trisubstituted benzenes

A

the directing effects of both substituents on a disubstituted benzene must be considered in deciding where the third group will add. the best situation is when both substituents direct to the same positions (ex. para so on either side of the molecule)

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34
Q

what beats what for trisubstituted benzens

A
  • the strong activator wins out over the weak activator
  • both substituents direct to different positions
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35
Q

describe halogenation of benzene with a strongly activating group present

A
  • halogenation of a ring with a strongly activating -OH and -OR substituent does not require a catalyst to add one halogen (ex. Br adds on easily)
    - once you stuck on the first bromine, you have to use the
    catalyst because you deactivated it enough
  • if a catalyst is used, substitution occurs at all ortho and para positions (ex. Br goes on three different places - almost looks like staggard conformation)
36
Q

explain halogenation with the strongest activating group present

A
  • aniline (for ex.) is so strongly activated that even triple halogenation does not require a catalyst.
  • to only halogenate the ring once: use acetylation (introduction of an acetyl functional group into a chemical compound), which reduces the -NH2 group slightly to activate it, so that the ring can be halogenated. the acetyl group can then be removed via base-promoted amide hydrolysis (NaOH + water)
37
Q

reactants used to put on an acetyl group for halogenation

A

acetyl group (ex. (CH3CO)2O) and pyridine

38
Q

reactants used to take off on an acetyl group for halogenation

A

NaOH and water

39
Q

why do we have to remove the acetyl group via base promoted amide hydrolysis

A

aniline cannot be nitrated directly because nitric acid will oxidize (be chemically combined with) an NH2 group. but, if the ring is protected by acetylation (acetyl group added) the ring can be nitrated.

40
Q

reactants used to help alkyl substituents to be oxidized to carbonyl groups

A

KMnO4
H2O

**key here is there are many oxygens

41
Q

can alkyl substituents be oxidized even if they aren’t attached to a benzene?

A

no

42
Q

reactants for free radical benzylic bromination

A

NBS and peroxide

43
Q

alkyl substituents oxidized to be carbonyl groups

A

benzene ring with an alkyl group becomes benzene ring with a -COOH group

44
Q

free radical benzylic bromination product

A

benzene-C(two hydrogens bonded)-CH2CH3 goes to benzene-C(one hydrogen and one bromine bonded)-CH2CH3 + NBS (that has an H instead of a Br)

45
Q

NBS

A

5 membered ring with N and two oxygen double bonds in the ortho position closest to N. The N is bonded to a Br

46
Q

does a bulky base encourage elimination or substitution

A

the use of a bulky base encourages elimination over substitution

47
Q

how do you reduce unsaturated substances

A

unsaturated substances –> have a double bond

reducing the double bond = making it a single bond

use: Pd/C

48
Q

what conditions is a benzene ring reduced at

A

high temps and high pressures

49
Q

what reactants remove all double bonds from benzene ring

A

H2, Pt, 130 atm, 25 degrees C

50
Q

what is an arenediazonium salt

A

benzene ring with an N triple bonded to N substituent and a Cl floating outside

51
Q

how do you synthesize NH2 to produce an arenediazonium salt

A

NaNO2, HCl at 0 degrees C

52
Q

what are arenediazonium salts used to generate

A

HONO (nitrous acid) in situ

53
Q

for the synthesis of a disubstituted benzene, how does reaction order matter

A

if the substituent is a meta director, the Br adds in the meta position. vs. if it was an ortho para director, which would add in the ortho / para position

note: if the substituent adds FIRST to the meta position, a Friedel-Crafts acylation will not occur (because it deactivates the ring).

54
Q

how can you use retrosynthetic analysis to determine what kind of substituent was used

A

see if the disubstituted benzene is in the meta or ortho / para position

55
Q

rule to remember about what carbons can perform what reactions

A

SN1 and SN2 reactions cannot perform a reaction on an sp2 carbon

56
Q

what reaction do aryl halides not react with

A

they don’t react with nucleophiles via an SN1 reaction because an aryl halide cation is too unstable toform
they don’t react with nucleophiles via SN2 because a nucleophile is repelled by the pi electron cloud and backside displacement is sterically impossible

57
Q

where can electrons be delocalized

A

electrons can be delocalized onto ortho and para substituents but cannot be delocalized onto a meta substituent

58
Q

How to add I on a benzene ring

A

I2 and H2O2

59
Q

how to add ONE Br to a benzene

A

FeBr3 and Br2

60
Q

how to add ONE Cl to a benzene

A

FeCl3 and Cl2

61
Q

how to add NO2 to a benzene

A

HNO3 and H2SO4

62
Q

how to add SO3H to a benzene

A

fuming H2SO4

63
Q

how to reduce an SO3H benzene to just a benzene

A

H3O+ and heat

64
Q

how to add CH2CH3 to a benzene

A

Cl-R (R=CH2CH3) and AlCl3

65
Q

how to add C(double bonded to O)-CH3 to a benzene

A

CH3C(double bonded O)Cl and AlCl3

66
Q

from a benzene with NO2, how do you change that substituent to NH2

A

H2 and Pd/C

67
Q

from a benzene with NH2, how do you change that substituent to N triple bonded to N+

A

NaNO2 and HCl

68
Q

from a benzene with NH2, how do you change that substituent to H-N-C(double bonded to O)CH3

A

CH3C(double bonded to O)Cl and pyridine

69
Q

from a benzene with H-N-C(double bonded to O)CH3, how do you change that substituent to a benzene with N-C(double bonded to O)CCH3 WITH an NO2 para

A

NHO3 and H2SO4

70
Q

from a benzene with N-C(double bonded to O)CCH3 WITH an NO2 para, how do you change that substituent to a benzene with NH2 WITH NO2 para

A

NaOH and H2O

71
Q

from a benzene with CH2CH3, how do you change that substituent to BrCHCH3

A

NBS and peroxide

72
Q

from a benzene with CH2CH3, how do you change that substituent to COOH

A

KMnO4

73
Q

from a benzene with BrCHCH3, how do you change that substituent to HOCHCH3

A

OH-

74
Q

from a benzene with BrCHCH3, how do you change that substituent to CH=CH2

A

OTS

75
Q

from a benzene with CH=CH2, how do you change that substituent to BrCHCH3

A

HBr

76
Q

from a benzene with CH=CH2, how do you change that substituent to HOCHCH3

A

H3O+

77
Q

from a benzene with CH=CH2, how do you change that substituent to CH2CH2Br

A

HBr and peroxide

78
Q

from a benzene with CH=CH2, how do you change that substituent to CH2CH2OH

A

BH3 and H2O2 and HO-

79
Q

from a benzene with N triple bonded to N+, how do you change that substituent to an F

A

HBF4 and heat

80
Q

from a benzene with N triple bonded to N+, how do you change that substituent to a Cl

A

CuCl

81
Q

from a benzene with N triple bonded to N+, how do you change that substituent to a Br

A

CuBr

82
Q

from a benzene with N triple bonded to N+, how do you change that substituent to an I

A

KI

83
Q

from a benzene with N triple bonded to N+, how do you change that substituent to an H

A

H3PO2

84
Q

from a benzene with N triple bonded to N+, how do you change that substituent to an OH

A

Cu2O and Cu(NO3)2 and H2O

85
Q

from a benzene with N triple bonded to N+, how do you change that substituent to a benzene connected to a C which is triple bonded to an N

A

CuCN

OCHEM 335 (7 decks)

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