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Chemistry > RPA - Nitrogen Compounds > Flashcards

RPA - Nitrogen Compounds Flashcards

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1
Q

Why must diazotisation and coupling reactions occur below 10 C?

A

To prevent decomposition. The diazonium salt is unstable

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2
Q

What are primary, secondary and tertiary amines?

A

Primary - one carbon group
secondary - two carbon groups
3 - three carbon groups bonded to nitrogen

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3
Q

Are amines soluble in water?

A

yes, because they form hydrogen bonds between H of NH2 and O of H2O

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4
Q

Is there a regular pattern of boiling points of amines?

A

No, as VdW forces add to the hydrogen bonding,

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5
Q

Are there hydrogen bonds on tertiary amines?

A

no, as no hydrogens on amine groups

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6
Q

What can ammonia be described as?

A

Alkali - releases OH- ions in solution

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7
Q

How do you prepare aliphatic amines? (Mechanisms, reagents,)

A

Nucleophilic substitution of halide with NH3 nucleophile

Ethanol conditions (No water to form OH- ions –> alcohol)
high pressure
hot

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8
Q

What are possible impurities in aliphatic amines?

A

Secondary/tertiary.

primary amines have lone pair on nitrogen so can act as nucleophiles to attack halogenoalkane

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9
Q

How can you reduce chance of impurities?

A

large excess of NH3 means more change of NH3 encountering halogenoalkane than primary amine

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10
Q

What is the method for preparation of phenylamine?

A

reduction of nitrobenzene using Sn/HCl reducing agent

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11
Q

What is the second stage in preparation of azo dye?

A

Reaction of phenylamine with NaNO2 to form diazonium ion

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12
Q

How is NaNO2 formed?

A

HCl + NaNO2 –> HNO2 + NaCl

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13
Q

What is the second stage in azo dye production, following diazonium ion formation?

A

Coupling reaction with phenol in alkaline conditions

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14
Q

Why are alkaline conditions used in coupling?

A

increases phenol reactivity by producing phenoxide ion by loosing one of the ring’s hydrogen

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15
Q

What is characteristic of an amino acid?

A

Amine and carboxylic acid group

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16
Q

What is an alpha amino acid?

A

one where NH2 and COOH is bonded to same carbon

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17
Q

What is a zwitterion?

A

a dipolar form of amino acid with NH3+ and COO- ions. Exists at isoelectric point of amino acid

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18
Q

What form do zwitterions exist in at their isoelectric point?

A

solids due to ionic bonding between molecules

19
Q

What happens when an amino acid is placed in alkaline conditions?

A

it acts as an acid, donates any protons on COOH groups to form negative ions

20
Q

What happens when an amino acid is placed in acidic conditions?

A

it acts as a base, and any NH2 groups accept protons to form NH3+ groups.

21
Q

What causes the intermolecular forces in amines to be intermittent?

A

Permanent dipole/H-bond interactions require direct alignment, which is not always the case.

22
Q

What is the mechanism for the production of secondary amines having produced primary aliphatic amine by nucleophilic substitution?

A

The nitrogen on primary amine still has lone pair, so can go on to react as a nucleophile with halogenoalkane, producing secondary amine

23
Q

What are the conditions when halogenoalkane undergoes nucleophilic substitution with NH3?

A

Ethanol (stop OH- ions forming)
High pressure
Hot

24
Q

What happens if an amino acid with a COOH group as the R group is placed in alkaline solution?

A

Both COOH groups act as acids, hence proton donors, hence BOTH become COO- groups

25
Q

What is required for a chiral centre?

A

Four different groups on a central carbon

26
Q

What are optical isomers?

A

2 non-superimposable mirror images (i.e. reflections)

27
Q

Given one molecule, how do you find the stereoisomers?

A

identify # chiral carbons, reflect the first, reflect the second, reflect both

28
Q

What does the (+) enantiomer of a stereoisomer do to plane polarised light?

A

Rotates by 90 clockwise

29
Q

What does the (-) enantiomer of a stereoisomer do to plane polarised light?

A

Rotates by 90 anticlockwise

30
Q

What does a racemic mixture of +- enantiomers do to plane polarised light?

A

Nothing, as the rotations cancel out

31
Q

What can be said about the optical activity of amino acids?

A

All alpha amino acids are optically active, except for glycine as this has only three different groups

32
Q

What is the actual shape of the molecules of an amino acid surrounding chiral carbon?

A

tetrahedral

33
Q

What happens when CH3CH2NH3 reacts with H2SO4?

A

Forms a salt:

CH3CH2NH3+ HSO4-

34
Q

Why are amines described as bases?

A

lewis bases as they donate protons,

Bronstead-Lowry bases as they accept protons to form NH4+ + OH-

35
Q

Can tertiary amines form hydrogen bonds?

A

No, as there must be a +ve H bonded to N/O/F, and there is not.

36
Q

What is the difference in boiling point between primary, secondary and tertiary amines?

A

Decreases as hydrogen bonding sites decrease

37
Q

What are the reactants in the first stage of synthesis of azo dyes?

A

HCl + HNO2

38
Q

What is the reaction to form HNO2, nitrous acid, in the synthesis of azo dyes?

A

HCl + NaNO2 –> HNO2 + NaCl

39
Q

What are the reactants in the second stage of formation of azo dye? What are the products other than the dye?

A

NaOH to produce H2O + NaCl

40
Q

Define condensation reaction

A

Joining of two + monomers to make a polymer by the elimination of a small molecule e.g. H2O/HCl

41
Q

Why is nitrogen a base?

A

NITROGEN electron pair accepts proton

42
Q

What must you consider when reducing a ring with multiple nitro groups?

A

How many moles of reducing agent and how many moles of water are produced

43
Q

What happens when a compound including amine groups is reacted with acid?

A

ALL the amine groups form ammonium ions. It does not matter whether they’re hydrolysed or not.

Chemistry (16 decks)

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