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Chemistry > Benzene and Its Compounds > Flashcards

Benzene and Its Compounds Flashcards

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1
Q

compound with one or more benzene rings

A

arenes

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2
Q

benzene compounds also known as

A

aryl/aromatic

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3
Q

describe the benzene ring

A

each carbon benzene is sp2 hybridised = delocalised electrons
benzene shape is planar (120 degrees)
overlap of p orbitals above and below ring
delocalised electrons in pi bonds spread over all six carbon atoms

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4
Q

describe kekule structure

A

benzene perfectly symmetrical hexagonal structure BUT C=C short
benzene cannot undergo addition reaction BUT structure has double bonds

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5
Q

what type of reaction do benzene undergo

A

electrophilic substitution

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6
Q

why does benzene only undergo certain reactions

A

high electron density
can only react with electrophiles but need halogen carrier
stable = pi bonding system

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7
Q

why is alkenes able to react whereas benzenes cannot

A

higher electron density

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8
Q

observation when arenes are combusted

A

smoky flames

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9
Q

describe halogenation of benzene (benzene + Br2)

A 
anhydrous iron (III) bromine/chlorine catalyst
electrophile (Br+) made by FeBr3 polarise Br2
electrophile and benzene react to form positive ion which turns into neutral molecule
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10
Q

draw the mechanism of benzene + Br2

A

picture

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11
Q

how do we get 4- chloromethyl benzene

A

chlorine gas and anhydrous aluminium chloride catalyst

halogenmethyl-benzene

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12
Q

which positions are activated with methylbenzene and cl2/br2

A

2,4,6 (excess)

OR 2/4

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13
Q

how do we get chloromethylbenzene ( substitution in methylchain)

A

UV light
chlorine gas
boiling methyl benzene

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14
Q

conditions for nitration of benzene

A

Concentrated nitric acid
Concentrated sulfuric acid
Reflux
55C

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15
Q

describe nitration of benzene process

A 
making electrophile (NO2+) by HNO3 + H2SO4
high electron dense pi bonding attracts electrophile
pair of electrons donate
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16
Q

what positions do NO2 group activate

A

3, 5 and deactivates 2,4

17
Q

describe process of alkylation of benzene

A

alcl3 catalyst + halogenoalkane

carbocation added to benzene ring

18
Q

which positions do carbocations substitute into methylbenzene

A

1,3 -
1,4 -
higher temperature produced more 1,3 -

19
Q

describe hydrogenation of alkylbenzene (reduction)

A

nickel catalyst
150 degrees
hydrogen gas

20
Q

alkylbenzene + hydrogen gas

A

→ cyclohexane

21
Q

how are side chains oxidised

A

reflux in acidified potassium manganate (VII)/acidified potassium dichromate + dilute h2so4

22
Q

products of oxidising side chains on benzene

A

carboxylic acid

23
Q

describe phenol

A

high melting point
slightly soluble due to hydrogen bonding OH
weakly acidic
more reactive than benzene

24
Q

why is phenol so reactive

A

oxygen lone pair delocalised in ring
greater electron density around ring
benzene ring is activated
attracts electrophiles

25
Q

rate on weak acidity
water
ethanol
phenol

A

phenol is the strongest

ethanol is the weakest

26
Q

comment on dissociation with weak acids/strong acids

A

weak partially dissociates - some stays as acid and some stays as ions
strong completerly dissociates

27
Q

why is phenol a weak acid (don’t be confused with reactivity)

A

phenoxide ion has negative charge spread - reduces charge density and negative ion is stable = stays as ions

28
Q

why is phenol a strong acid than ethanol

A

ethanol has electron donating group that concentrates negative charge on oxygen - making it more attracted to hydrogen and able to reform

29
Q

what are the reactions with phenols (4)

A

Phenol + NaOH → salt + water
2Phenol + Na → 2salt + hydrogen gas
Phenol + Na2CO3 → NaHCO3 + sodium phenoxide
Phenol + 3Br2 → 2,4,6-tribromophenol (white ppt.) + 3HBr

30
Q

how do you produce 2,4,6 trinitrophenol

A

room temperature

dilute nitric acid

31
Q

what are electron donating groups

A

alkyl groups

32
Q

what are electron withdrawing groups

A

electronegative groups

Chemistry (15 decks)

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