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Chemistry Year 13 > Aromatic Compounds > Flashcards

Aromatic Compounds Flashcards

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1
Q

What is kekule model of benzene

A

Alternating c-c, c=c bonds

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2
Q

What is the evidence against kekules module

A

Lack of reactivity of benzene (benzene does not undergo electrophilic addition reactions, does not decolourise bromine under normal conditions)

Lengths of C-C bonds, all bonds are same length

Hydrogenation enthalpies (should be 3X one hydrogenation of a double bond which is -120 but benzene is -208. This shows benzene is more stable)

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3
Q

Describe the delocalized model of benzene (the newest one)

A

Benzene is planar, cyclic,hexagonal hydrocarbon ( C6H6)

Each C uses 3 of its 4 available electrons in binding to two other C and one to H

Each C has one electron in a P orbital at right angles to the plane of the bonded C and H

Adjacent P orbitals electrons overlap sideways above and below the plane of C’s to form a ring of electron density

The overlapping of P orbitals creates a system of pi-bonds which spread over all C’s in the ring structure

6 electrons occupying the system of pi-bonds are delocalized

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4
Q

What groups are considered prefixes to benzene

A

Alkyl groups (CH3,C2H5)
Halogens (F,Cl,Br,I)
Nitro (NO2)

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5
Q

When is benzene considered the substituent and what prefix is used

A

Phenyl
When bending ring attached to alkyl chain with a functional group or 7 or more carbons attached

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6
Q

What is the name of a benzene ring attached to C2H5

A

Ethylbenzene

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7
Q

What is the name of a benzene ring attached to chlorine

A

Chlorobenzene (1,2-dichlorobenzene if more then one for eg)

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8
Q

What is the name for a benzene ring attached to NO2

A

Nitrobenzene

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9
Q

What is name for a benzene ring attached to a COCH3

A

Phenylethanone

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10
Q

What is name for a benzene ring attached to CH3HC6H13

A

2- phenyloctane

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11
Q

What is name for a benzene ring attached to COOH

A

Benzoic acid

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12
Q

What is name for benzene attached to NH2

A

Phenylamine

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13
Q

What is the name for benzene attached to CHO

A

Benzaldehyde

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14
Q

Describe an electrophilic substitution mechanism

A

Electrons from ring of benzene curly arrowed to electrophile
Then the electrophile is attached with H, 2/3 of benzene ring covered with a + symbol in it
Electrons from H move to the gap in the benzene ring
Electrophile now attached where H was and H+ released

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15
Q

Describe conditions and reactions of nitration of benzene

A

Benzene + (conc)HNO3——> nitrobenzene + H20

Catalyst: conc H2SO4
Temperature: 50^C

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16
Q

Describe the reaction to produce the electrophile for nitration of benzene

A

(Conc) HNO3 + (conc) H2SO4—-> H2NO3+ + HSO4-
H2NO3+——-> H20 + NO2+

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17
Q

What happens if the temperature fur by nitration of benzene rises above 50^C

A

Further substation reactions can occur leading to production of dinitrobenzene

18
Q

How is H2SO4 a catalyst in nitration of benzene

A

HSO4- + H+ released= H2SO4
Therefore is used in reaction but is regenerative

19
Q

How does benzene react with halogens

A

With a halogen carrier
Eg FeCl3, AlBr3, FeBr3

These can be generated in situ

20
Q

Describe mechanism for bromination of benzene

A

Br2+ FeBr3—> FeBr4- + Br+

Br+ then added by electrophilic substitution

H+ + FeBr4——> FeBr3 + HBr

21
Q

Chlorination of benzene

A

Same as bromination but with chlorine

22
Q

Alkylation reactions with benzene, what is needed what happens

A

Catalyst: haloalkane (eg AlCl3)

Benzene + C2H5Cl——-> ethylbenzene + HCl

23
Q

Acylation reactions, what is needed, what happens

A

Catalyst: AlCl3

Benzene + ethanoyl chloride——> phenylethanone + HCl

24
Q

Why are alkenes more reactive then benzene

A

Alkenes react with grooming by electrophilic addition,
Benzene’s delocalized pi electrons are spread out above and below ring of 6 C’s, the electron density around any 2 C atoms is less then in the C=C bond in alkene

When non polar molecule approaches benzene there is insufficient pi electron density to polarize the molecule

25
Q

What are phenols

A

Benzene ring with a hydroxyl (-OH) functional group attached to

26
Q

When naming phenols what take priority as C number 1
Eg: phenol with COOH

A

OH group takes Carbon number 1

Eg 2-hydroxybenzoic acid

27
Q

Why is phenol less soluble in water then alcohols

A

Due to the presence of the non-polar benzene ring.

28
Q

Why is phenol a weak acid

A

When dissolved in water, phenol partially dissolves into phenoxide ion and a proton

29
Q

Order the acidity of phenols, alcohols, carboxylic acids from strongest to weakest

A

Carboxylic acid
Phenol
Alcohol

Alcohols don’t react with strong bases
Phenols only react with strong bases
Carboxylic acids react with strong and weak bases

30
Q

Describe the reaction of phenol with sodium hydroxide and

A

Benzene ring attached to O- Na+
And H2O

31
Q

Describe bromination of phenol

A

Phenol + aqueous solution of bromine to form 2,4,6 tribromophenol

Phenol + 3Br2—-> 2,4,6 tribromophenol + 3HBr

32
Q

Describe describe nitration of phenol

A

Phenol + HNO3———> 2 OR 4 nitrophenol

33
Q

Why is phenol more reactive then benzene

A

PHENOL: Lone pair of electrons from O p-orbital of the OH group is partially delocalized into the pi-electron system of phenol. The electron density of benzene ring is therefore increased which means it is more readily attracted to electrophiles more strongly then benzene

34
Q

Why is phenol more reactive then benzene

A

PHENOL: Lone pair of electrons from O p-orbital of the OH group is partially delocalized into the pi-electron system of phenol. The electron density of benzene ring is therefore increased which means it is more readily attracted to electrophiles more strongly then benzene

35
Q

Describe reaction of bromine with phenylamine

A

No halogen catalyst required

Phenylamine + 3Br2——-> 2,4,6 directing bromine

36
Q

Describe reaction of nitrobenzene with bromine

A

Nitrobenzene + Br2—-> 3-beomonitrobenzrne + HBr

37
Q

What groups are 2,4 directing

A

NH2, NHR
OH
OR
R, C6H5
F,Cl,Br,I

Generally have lone pair of electrons except from halogens

38
Q

What groups are 3 directing

A

RCOR
COOR
SO3H
CHO
COOH
CN
NO2
NR3+

39
Q

What are the activating groups

A

All 2,4 directing groups with exception of halogens

40
Q

What are the deactivating groups

A

All 3 directing groups

Chemistry Year 13 (3 decks)

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