Aromatic compounds and benzene Flashcards by Nicole Brotherston

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

all of them are the same length and strength

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T or F: benzene is planar

true

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describe the electron clouds in benzene

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

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is benzene aromatic?

yes

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T or F: benzene is an annulene

true

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what is an annulene

conjugated monocyclic hydrocarbon

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how do you name annulenes

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

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T or F: all annulenes are aromatic

false! not all of them are

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name the benzene compound based on the substituent: methyl

toluene

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name the benzene compound based on the substituent: COOH

benzoic acid

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name the benzene compound based on the substituent: OH

phenol

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name the benzene compound based on the substituent: COH

benzaldehyde

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name the benzene compound based on the substituent: OCH3

anisole

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name the benzene compound based on the substituent: COCH3

acetophenone

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name the benzene compound based on the substituent: NH2

aniline

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name the benzene compound based on the substituent: CN

benzonitrile

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T or F: benzene can form polycyclics

true

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

napthalene

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

anthracene

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

phenanthrene

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

pyrene

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describe the placement of the substituents in the ortho prefix

right beside each other (1 and 2)

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describe the placement of the substituents in the meta prefix

two away from each other (1 and 3)

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describe the placement of the substituents in the para prefix

at opposite sides to each other (1 and 4)

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

the highest priority sub is on carbon one

T or F: benzene is unstable

false; it is stable

T or F: benzene is highly reactive

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

list the three reasons why benzene isn't reactive

- 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

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

- 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

T or F: conjugate base aromaticity increases acidity

true

why does conjugate base aromaticity increase acidity

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

are anti-aromatic compounds stable or unstable

unstable

are anti-aromatic compounds reactive or unreactive

highly reactive

what is the rule for anti-aromatic compounds

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

what happens to the aromaticity of benzene if it reacts

benzene will lose aromaticity

when benzene reacts, are the products or reactants favored

reactants are favored because the product is uphill

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

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

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

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

what lewis acid do we use in halogenation

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

describe the halogenation reaction

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

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

NO2

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

true

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

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

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

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

describe the acidification of nitric acid by H2SO4

- 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

in nitrogenation, describe the reaction of benzene with NO2+

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

what are we trying to add to benzene in sulfonation

SO3H

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

H2SO4 = SO3 + H2O | reactants are favored

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

heat!

describe the sulfonation mechanism

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

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

react it with dilute H2SO4

what are we trying to make with friedel-crafts alkylation

a benzene with an alkyl group attached (mono addition)

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

use a lewis acid and an alkyl halide as an electrophile

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

true; practice this

describe the limits to alkylation

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

how do we add a long hydrocarbon chain onto a benzene

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

what is an acyl halide

carbonyl attached to R and X

what is the product of friedel-crafts acylation

a benzene with carbonyl attached to R on it

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

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

what happens if we use anhydrides in friedel-crafts acylation

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

Aromatic compounds and benzene Flashcards

(60 cards)