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Chemistry > 6.1 > Flashcards

6.1 Flashcards

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1
Q

what is benzene

A

benzene is a naturally occurring aromatic compound, which is very stable planar ring structure with delocalised electrons

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2
Q

molecular and empirical formula of benzene

A

CH

C6H6

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3
Q

what is the Kekulé structure of benzene

A

σ bonded ring
3 alternating π bonds
highly unsaturated (so expected to be reactive)

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4
Q

3 pieces of experimental evidence against the Kekulé structure of benzene

A

1) benzene is resistant to undergo electrophilic addition (unlike alkenes) which shows there is no true C=C bond
2) enthalpy of hydrogenation is lower than expected so more stable than expected
3) x-ray diffraction techniques showed that the bond lengths are are all equal (whereas normally single bonds are longer then double bonds, these bonds are somewhere in between)

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5
Q

structure of benzene

A

benzene has a ring of 6 σ bonds, and the p-orbitals overlap causing a delocalised electron structure.
planar structure
6 σ bonds and 6 π electrons

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6
Q

does benzene undergo electrophilic addition

A

no, electrophilic substitution instead

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7
Q

what catalyst is required for chlorination of benzene (halogenation)

A

a halogen carrier

FeCl3 or AlCl3

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8
Q

overall equation for chlorination of benzene (halogenation)

A

C6H6 + Cl2 –> C6H5Cl + HCl

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9
Q

3 steps in chlorination of benzene (halogenation)

A

(electrophile generation) Cl2 + FeCl3 FeCl4- + Cl+
(curly arrow mechanism)
(catalyst regeneration) H+ + FeCl4- –> HCl + FeCl3

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10
Q

reagents needed in nitration of benzene

A

conc. nitric acid HNO3 and conc. sulphuric acid H2SO4 (catalyst)

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11
Q

overall equation of nitration of benzene

A

C6H6 + HNO3 –> C6H5NO2 + H2O

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12
Q

electrophile generation step of nitration of benzene

A

H2SO4 + HNO3 HSO4- + H2O + NO2+

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13
Q

catalyst regeneration step of nitration of benzene

A

H+ + HSO4- –> H2SO4

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14
Q

why is the friedel-crafts reaction useful

A

allows carbon chains to be added to benzene rings which is very important in synthesis

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15
Q

catalyst for friedel-crafts

A

halogen carrier- FeCl3 or AlCl3

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16
Q

what is phenol?

A

phenol is a benzene ring with an OH group on them

17
Q

is phenol more electron dense that benzene ?

A

yes, because the lone pair on the oxygen in a p-orbital overlaps with the p-orbitals in benzene so the oxygen electrons are (partially) delocalised into the ring.

18
Q

what is different (3 things) about electrophilic substitution with phenol rather then benzene

A
  • phenol reacts more readily then benzene so can undergo POLYsubstition (rather than mono) WITHOUT a catalyst for both halogenation and nitration
  • the OH groups acts as a donating group due to the lone pair so directs the substitutes to the 2,4, (6) positions
19
Q

is phenol an acid or alkali

A

phenol is a weak acid, and will dissolve slightly in water to form weak acidic solution
it is a stronger acid than aliphatic alcohols as the ring helps weaken the OH bond so the H is more easily lost

20
Q

does phenol ungergo the normal acid reactions

acid + metal, acid +metal hydroxide, metal carbonate + acid

A

reacts with metals and metal hydroxides BUT NOT metal carbonates

21
Q

how can you identify if you have phenol

A

if it has an acidic pH but NOT with metal carbonate

also a white precipitate is formed when electrophilic substitution with bromine

22
Q

what is Brady’s reagent

A

2,4-dinitrophenylhydrazine

23
Q

what is 2,4-dinitrophenylhydrazine also known as

A

Brady’s reagent

24
Q

what is a simple chemical test with Brady’s reagent and what does it tell you

A

it forms an orange precipitate when reacted with aldehydes and ketones

25
Q

what is a more complex test with Brady’s reagent

A
  • purify the orange precipitate formed
  • find the melting point
  • look up in data base to find the exact aldehyde or ketone
26
Q

what is Tollen’s reagent

A

ammonical silver nitrate

27
Q

what is ammonical silver nitrate also known as

A

Tollen’s reagent

28
Q

what is a simple chemical test with Tollen’s reagent

A

reacts with aldehydes and turns into a carboxylic acid as it is a mild oxidizing agent -
a ‘silver mirroring’ effect is formed as the Ag+NO3- is reduced to Ag (silver is formed)

Chemistry (12 decks)

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