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Chemistry > Aromatics + Amines > Flashcards

Aromatics + Amines Flashcards

1
Q

In alkenes carbon atoms are..

A

Sp2 hybridised

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2
Q

What are double bonds and how are they formed

A
  • One 2s orbital and two of the 2p orbitals in the carbon atom hybridise to form 3 sp2 orbitals.
  • one p orbital is left over and is orientated perpendicular to the plane of others
  • single bonds between C and H are sp2 orbitals as overalapping with 1s orbitals in H
  • double bonds overlapping of two adjacent sp2 orbitals and the overlap between leftover p orbitals
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3
Q

What is a conjugated system

A
  • a system of connected p orbitals with delocalised electrons in a molecule
  • lowers the overall energy of the molecule and increases stabili8ty
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4
Q

How is a continuous system formed?

A
  • unhybridised p orbitals can overlap
  • pi electrons can be delocalised through this
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5
Q

Where can continuous systems occur

A

In any molecule when two double bonds are separated by one single bond

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6
Q

Why does the delocalisation of the pi electrons makes molecules more stable when there is a continuous system?

A
  • electrons can spread out over the molecule so there is less repulsion
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7
Q

How is stability of alkenes and dienes measured?

A
  • hydrogenation enthalpy data
  • less exothermic the reaction between the double bonds and hydrogen the more stable the molecule
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8
Q

What is benzene?

A
  • a liquid compound C6H6
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9
Q

What was August kekule theory about benzene?

A
  • ringed structure with 6 carbon atoms and 6 hydrogen atoms
  • he suggested that the bonding consisted of alternating double and single bonds
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10
Q

What chemical features does benzene that disproves kekules theory

A
  1. Benzene does not undergo addition reaction
  2. All bonds are equivalent in terms of length and strength
  3. Stability
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11
Q

Explain the differences in stability that are observed when benzene is hybridised

A

If kekules theory is right, you would expect arround 3x ΔH Hyd released but you get much less

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12
Q

What reaction does benzene undergo?

A
  • electrophilic substitution reaction
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13
Q

Give the outline of the mechanism for electrophilic substitution

A
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14
Q

Describe Friedan crafts acylation

A
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15
Q

Describe nitration electrophilic substitution

A
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16
Q

How do we form nitrobenzene

A

Benzene + conc HNO3 -> Nitrobenzene + water

Conc sulphuric acid catalyst

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17
Q

What is the IUPAC name for TNT?

A

2,4,6 - trinitromethylbenzene

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18
Q

Why is TNT a good explosive?

A
  • reaction of tnt with oxygen is extremely exothermic
  • produces a lot of gas rapidly (11 moles for every mole of TNT used) along with a lot heat
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19
Q

What else are aromatic amines use for?

A

Industrial dyes called azo dyes

20
Q

How do you get phenylamine from nitrobenzene

A

Reduction reaction using Sn/Hcl

21
Q

Describe the pH of phenylamine

A

Weak base

22
Q

What does the strength of a base depend on?

A

Availability of the lone pair:
How easily the lone pair becomes protonated

23
Q

Why is phenylamine a weak base?

A
  • the lone pair on the N atom is delocalised into the Pi system on the benzene ring and so i less available
24
Q

What is an amine called when there are four carbons connected to the nitrogen atom

A

Ammonium salt

25
Q

What is the name of the shape and bond angle for primary to tertiary amines

A

Trigonal pyramidal 107

26
Q

What is the name of the shape and bond angle for an ammonium salt

A

Tetrahedral 109.5

27
Q

How do you name primary amines

A

Alkyl amine

28
Q

How do you name an a amine group which is in the middle of the chain or isn’t the PFG

A

amino

29
Q

How do you name secondary and tertiary amines?

A

Secondary and tertiary amines are effectively N-substituted amines, so we need an N- at the start of the name so we know these substituents are attached to the N atom. The alkyl group with the longest carbon chain form the main stem of the name of the amine, so the alphabetical rule for naming is violated.

30
Q

Why do amines have higher boiling points than their analogous alkenes

A

H - bonds > vow

31
Q

Why do amines have a lower boiling points than than their analogous alcohols

A
  • NH bond is not as polar as the OH bonds
  • hydrogen bonds between molecules are weaker in amines
32
Q

Why are amines soluble in water but solubility decreases as chain length increases

A

Larger proportion of chain is non-polar
Disrupts H bonding between H molecules

33
Q

Why do amines form alkaline solutions

A

Release an OH- in water
RNH2 + H2O <-> RN+H3 + OH-

34
Q

Why can amines act as bronsted Lowry bases? (Proton acceptor)

A
  • they gain a proton from water and can react with acids

RNH2 + HCl -> RNH3+Cl-

35
Q

What is the equation for methyl amine and sulphuric acid

A

2CH3NH2 + H2SO4 -> (CH3N+H3)2SO42-

Methylammoniumsulphate

36
Q

How would the base strength of phenylamine compare to ammonia or methylamine?

A
  • weaker because the lone pair in the pi system makes it less available to act as a proton acceptor
37
Q

Order the follow types of amine in order of decreasing base strength: ammonia, primary amine, secondary amine, tertiary amine, aromatic amine

A

Tertiary > secondary > primary > ammonia > phenylamine/aromatic

38
Q

What are the three ways to prepare amines?

A

Aliphatic:
1. Nucleophilic substitution - reaction of NH3 with halogenalkanes
2. Reduction of nitriles
Aromatic:
3. Nitration or Reduction

39
Q

Describe the reaction of NH3 with halogenalkanes

A

Nucleophilic substitution

Chloroethane and ammonia
Excess ammonia

Ethylamine and ammonium chloride

40
Q

Describe the reduction of nitriles to form an amine

A

Start with halogenalkanes
Step 1: reaction between halogenalkane (bromoethane and KCN)

Nucleophilic substation - warm and ethanoic

Propanitrile

Step two: reduce propane nitrile
Use H2 or Ni / ([H])

41
Q

Why is reduction of nitriles better than Nucleophilic substation of halogenalkane

A

Produces pure primary amine with no poly substitution
Higher atom economy
However KCN is toxic

42
Q

Why is the product of a Nucleophilic substitution reaction with a bromoalkane an even better Nucleophilic than the ammonia starting reagent?

A

Electron density is push by the alkyl group towards the nitrogen atom making the lone pair or electron density even more available to act as a Nucleophilie

43
Q

What is polysubstittuion

A

When Nucleophilic substitution occurs again and again

44
Q

How do we prevent and promote polysubstitution

A
  • excess ammonia
  • excess halogens alkane
45
Q

What are some uses of quaternary ammonium salts

A
  • production of catrionic surfactants
  • found in detergents, fabric softeners and hair conditions
  • coat the surface of cloth or hair with positive charges and reduce static due to negatively charged electrons

Chemistry (14 decks)

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