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CHEM 2420- organic chem 2 > Aromatic compounds and benzene > Flashcards

Aromatic compounds and benzene Flashcards

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1
Q

describe the length and strength of the C-C bonds in benzene

A

all of them are the same length and strength

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2
Q

T or F: benzene is planar

A

true

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3
Q

describe the electron clouds in benzene

A

the benzene has ring shaped delocalized pi electron clouds above and below the planar molecule

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4
Q

is benzene aromatic?

A

yes

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5
Q

T or F: benzene is an annulene

A

true

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6
Q

what is an annulene

A

conjugated monocyclic hydrocarbon

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7
Q

how do you name annulenes

A

[n]annulene, where n=number of carbons in the ring

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8
Q

T or F: all annulenes are aromatic

A

false! not all of them are

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9
Q

name the benzene compound based on the substituent: methyl

A

toluene

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10
Q

name the benzene compound based on the substituent: COOH

A

benzoic acid

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11
Q

name the benzene compound based on the substituent: OH

A

phenol

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12
Q

name the benzene compound based on the substituent: COH

A

benzaldehyde

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13
Q

name the benzene compound based on the substituent: OCH3

A

anisole

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14
Q

name the benzene compound based on the substituent: COCH3

A

acetophenone

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15
Q

name the benzene compound based on the substituent: NH2

A

aniline

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16
Q

name the benzene compound based on the substituent: CN

A

benzonitrile

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17
Q

T or F: benzene can form polycyclics

A

true

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18
Q

name the polycyclic based on the number of rings/their arrangement: 2 in a line

A

napthalene

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19
Q

name the polycyclic based on the number of rings/their arrangement: 3 in a line (straight)

A

anthracene

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20
Q

name the polycyclic based on the number of rings/their arrangement: 3 in a line (bent)

A

phenanthrene

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21
Q

name the polycyclic based on the number of rings/their arrangement: 4 in a cluster

A

pyrene

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22
Q

describe the placement of the substituents in the ortho prefix

A

right beside each other (1 and 2)

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23
Q

describe the placement of the substituents in the meta prefix

A

two away from each other (1 and 3)

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24
Q

describe the placement of the substituents in the para prefix

A

at opposite sides to each other (1 and 4)

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25
Q

for disubstituted benzenes, which sub is labelled as carbon one?

A

the highest priority sub is on carbon one

26
Q

T or F: benzene is unstable

A

false; it is stable

27
Q

T or F: benzene is highly reactive

A

false; it is stable, so it doesn’t want to react

28
Q

list the three reasons why benzene isn’t reactive

A
  • all the bond lengths are the same
  • all carbons are sp2 hybridized and each p orbital overlaps equally with its 2 neighbors
  • it’s resonance stabilized
29
Q

what are the criteria for a molecule to be aromatic (there’s 4)

A
  • contain 4n+2 electrons (in pi and/or lone pairs), where n=0,1,2,3…
  • delocalized electrons must be in one or more rings
  • must be conjugated
  • must be planar
30
Q

T or F: conjugate base aromaticity increases acidity

A

true

31
Q

why does conjugate base aromaticity increase acidity

A

when an acids conj. base is aromatic, it is stable. Stable conjugate bases=super strong acids=increased acidity

32
Q

are anti-aromatic compounds stable or unstable

A

unstable

33
Q

are anti-aromatic compounds reactive or unreactive

A

highly reactive

34
Q

what is the rule for anti-aromatic compounds

A

contain 4n electrons. All the other criteria is the same as the criteria for aromatic compounds

35
Q

what happens to the aromaticity of benzene if it reacts

A

benzene will lose aromaticity

36
Q

when benzene reacts, are the products or reactants favored

A

reactants are favored because the product is uphill

37
Q

how can we increase the difference in electron density between the reactions so the product is favorable (in benzene reactions)

A

use a lewis acid to accept the electrons and make a better electrophile

38
Q

when we use lewis acids for benzene reactions, what type of product do we get (hint: reaction will give us addition)

A

we get a product that underwent mono addition (not anti-addition like we would expect)

39
Q

what lewis acid do we use in halogenation

A

AlBr5 (where Al is neg, and one of the Br is pos)

40
Q

describe the halogenation reaction

A

benzene reacts with the lewis acid, picking off it’s electrophilic Br. When this happens, we get an intermediate that is a resonance stabilized sigma complex. Then there is a proton transfer and the lewis acid is regenerated (catalyst), and the pi bond is reformed and we’ve done mono addition to the benzene

41
Q

in a nitration reaction, what are we looking to add to the benzene

A

NO2

42
Q

T or F: for nitration, using a traditional lewis acid isn’t great

A

true

43
Q

explain why traditional lewis acids aren’t very good in nitration reactions

A

if we react benzene with NO2 and a lewis acid, we get a low yield, harsh conditions, and side products

44
Q

in nitration, what do we use instead of a lewis acid + why

A

H2SO4, because nitric acid (HNO3) is acidified by it

45
Q

describe the acidification of nitric acid by H2SO4

A
  • basically combining nitric acid and sulfuric acid together
  • nitric acid deprotonates sulfuric acid
  • the product is a cation (NO2+), which benzene cannot resist
  • therefore, right as NO2+ is made, it reacts with benzene
46
Q

in nitrogenation, describe the reaction of benzene with NO2+

A

benzene attacks N+ of NO2+, we get a new sigma bond that came from pi electrons, we get the sigma complex, then we deprotonate using sulfuric acid and drive towards benzene. Another proton transfer, and the sulfuric acid is regenerated and we’re left with mono addition of NO2 on benzene

47
Q

what are we trying to add to benzene in sulfonation

A

SO3H

48
Q

describe the SO3 equilibrium (and which side the equilibrium lays)

A

H2SO4 = SO3 + H2O

reactants are favored

49
Q

how can we drive the H2SO4 and SO3 equilibrium to the products to get more SO3

A

heat!

50
Q

describe the sulfonation mechanism

A

benzene attacks SO3, sulfonic sigma complex, proton transfer to make SO3- into SO3H, and we’re done

51
Q

how do we convert a benzene with SO3H on it back into regular benzene

A

react it with dilute H2SO4

52
Q

what are we trying to make with friedel-crafts alkylation

A

a benzene with an alkyl group attached (mono addition)

53
Q

what do we use to add an alkyl group onto a benzene

A

use a lewis acid and an alkyl halide as an electrophile

54
Q

T or F: friedel-crafts alkylation may also be intramolecular

A

true; practice this

55
Q

describe the limits to alkylation

A

if the alkyl group is more than 2 carbons, a mixture of products is formed, and the number of side products increases as the alkyl halide grows

56
Q

how do we add a long hydrocarbon chain onto a benzene

A

use a lewis acid and an acyl halide as an electrophile (friedel-crafts acylation)

57
Q

what is an acyl halide

A

carbonyl attached to R and X

58
Q

what is the product of friedel-crafts acylation

A

a benzene with carbonyl attached to R on it

59
Q

in friedel-crafts acylation, how do we get rid of the carbonyl on benzene

A

wittig or clemmensen to reduce the carbonyl. It leaves the chain and R attached

60
Q

what happens if we use anhydrides in friedel-crafts acylation

A

the method is analogous to that using acyl halides, because both have good leaving groups. We’re left with a benzene with a carbonyl attached

CHEM 2420- organic chem 2 (10 decks)

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