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chemistry A-level 2 > aromatic compounds > Flashcards

aromatic compounds Flashcards

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1
Q

what is benzene

A

aromatic compound consisting of a ring of 6 carbon atoms with 6 hydrogen atoms and a ring of delocalized electrons

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2
Q

what are the bonds in benzene like

A

each bond has an intermediate length in-between a double and single bond

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3
Q

the outer electrons in benzene

A

outer electrons from the p orbital of each carbon atom are delocalised to form the central ring. this ring makes benzene very stable compared to other molecules of a similar size

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4
Q

what was the prediction of benzenes enthalpy structure

A
  • predicated it had similar structure to cyclohexatriene (3 double bonds & 3 single)
  • expected the enthalpy change of hydrogenation for benzene was to be 360kjmol-1 (3x cyclohexene)
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5
Q

what is the actual enthalpy change of hydrogenation of benzene

A

-208kjmol-1
so it’s a different, unusual structure

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6
Q

what are arenes/aromatic compounds

A

compounds that contain benzene as part of their structure

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7
Q

features of arenes/aromatic compounds

A
  • high melting points due to high stability of the delocalized ring
  • low boiling points as the are non-polar molecules and often cannot be dissolved in water
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8
Q

nitration
generation of an electrophile

A

H2SO4 + HNO3 -> HSO4- + H2NO3+
concentrated acid and base

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9
Q

nitration
generation of an electrophile
intermediate

A

H2NO3+ -> NO2+ + H2O
nitronium ion 0 electrophile
H2SO4 + H2O -> HSO4- + H3O+

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10
Q

nitration
generation of an electrophile
overall

A

HNO3 + 2H2SO4 -> NO2+ 2HSO4- + H3O+

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11
Q

what do we need for acylation

A
  • catalyst - AlCl3
  • acyl chloride
  • anhydrous conditions
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12
Q

acylation
C2H3OCl + AlCl3 ->

A

C2H3OCl + AlCl3 -> C2H3O+ + AlCl4-

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13
Q

acylation - mechanism
H+ + AlCl4- ->

A

AlCl3 + HCL
AlCl3 - catalyst

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14
Q

nucleophilic substitutions of an amine

A

the reaction of halogenoalkane with ammonia sealed tube. 1 mole of halogenoalkane reacts with two moles of ammonia producing a primary amine and an ammonium salt

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15
Q

nucleophilic substitution producing a quarternary ammonium salt

A

substitution can continue until all the hydrogen atoms have been replaced

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16
Q

what are the problems with nucleophilic substitution with amines

A

mixture of products are produced. the reaction has low efficiency and the conditions have to be changed so only one substitution occurs

17
Q

how to produce a primary amine

A
  • ammonia added in excess
  • or mixture of products can be separated using fractional distillation
18
Q

reduction of nitriles to produce amines

A

hydrogenation. requires LiAlH4, a reducing agent and acidic conditions or a combination of hydrogen and nickel (catalytic hydrogenation)

19
Q

how to produce aromatic amines

A

produced from the reduction of nitrobenzene using conc. HCL and tin catalyst, room temp

20
Q

cationic surfactants

A

moelcuesl with +ve & -ve end. good conditioners as two ends attract different substances, preventing static from building up on surfaces

21
Q

amines as a base

A

weak bases due to the lone electron pair on the nitrogen atom can accept protons

22
Q

what does the base strength depend on

A

depends on how available the electron pair is on the molecules. the more available the electrons, the more likely it is to accept a proton meaning a stronger base

23
Q

strongest to weakest base

A
  • tertiary amine
  • secondary amine
  • primary amine
  • ammonia
  • phenyl amine
  • diphenyl amine
  • triphenyl amine
24
Q

suitable isotopes for nuclear magnetic resonance

A
  • 1H NMR
  • 13C NMR
  • 31P NMR
  • 19F NMR
25
Q

1H NMR

A
  • main type of NMR
  • give lots of structural information
  • quick (1 minute)
26
Q

13C NMR

A
  • not as common as “it takes too long” 5 minutes
  • there are only time amounts of 13C in sample most of its 12C
27
Q
A
27
Q

Tetramethlysilane (TMS)

A
  • added to a sample to calibrate the spectrum
  • the TMS chemical to 0
  • it is used because signal is away from everything else
  • only gives on strong signal
  • non toxic and inert (not reactive)
  • low bp so can be removed from a sample easily

chemistry A-level 2 (6 decks)

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