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Nitrogen Compounds Flashcards

1
Q

What are the types of nitrogen compounds?

A
  • amine
  • amide
  • amino acid
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2
Q

What are amines?

A

Derivatives of NH3 where one of more of the hydrogen atoms in of the ammonia molecule has been replaced by alkyl or aryl group

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3
Q

What is the general formula for primary amines?

A

NH₂R

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4
Q

What is the general formula for secondary amines?

A

NHR’R’’

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5
Q

What is the general formula for tertiary amines?

A

NR’R’‘R’’’

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6
Q

What is the general formula for quaternary ammonium ion?

A

[RNR’R’‘R’’’]⁺

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7
Q

What is the shape of amines?

A

trigonal pyramidal

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8
Q

What is the shape of quaternary ammonium ion?

A

Tetrahedral

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9
Q

How to name amines?

A

When 2 or more alkyl groups are attached to N of amines, the shorter chains of alkyl groups are treated as substituents

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10
Q

What are the properties of small aliphatic amines?

A

They are gases with characteristic ammonia smell

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11
Q

What are the properties of amines of higher Mr?

A

Liquids with fishy odour

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12
Q

What happens to boiling point of primary amines as the number of carbon atom increases?

A

As the number of carbon atom increases, the number of electrons in the molecule increases, more energy is required to overcome the stronger id-id

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13
Q

For isomeric amines, how do the boiling points of primary and secondary amines compare with tertiary amines?

A
  • primary and secondary amines > tertiary amines
  • Primary and secondary amines have higher boiling points than their isomeric tertiary amines due to their ability to form intermolecular hydrogen bonds, while tertiary amines cannot form hydrogen bonds
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14
Q

Are amines soluble in water?

A

-lower members of aliphatic amines are very soluble in water
- due to lone pair of electrons on N atom, all amines can form hydrogen bonds with water molecules

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15
Q

What happens to the solubility of amines as the number of C atom increases?

A

As the number of carbon atom increases, solubility of amines decreases because the bulky, non-polar alkyl/aryl group hinder the formation of hydrogen bonds between amine and water molecules

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16
Q

What can amines act as?

A

Bases, nucleophiles and ligands

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17
Q

What is a Bronsted-Lowry acid?

A

A proton donor

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18
Q

What is Bronsted-Lowry base?

A

A proton acceptor

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19
Q

What is Lewis acid?

A

Electron pair acceptor

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20
Q

What is Lewis base?

A

Electron pair donor

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21
Q

When does amine act as a Bronsted-lowry base?

A

In aqueous medium

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22
Q

What is the general equation for amine in water?

A

RNH₂ + H₂O ⇌ RNH₃⁺ + OH⁻

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23
Q

What is the structure of RNH₃⁺ like?

A

[R-N(H₂)→H]⁺

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24
Q

Why can amine act as a Bronsted-Lowry base?

A

Amines can act as a base due to the availability of a lone pair of electrons on its N atom for protonation, an amine accepts the proton by forming a dative covalent bond with it

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25
Q

What does a larger Kb value mean?

A

The larger the Kb value, the greater the proportion of amine molecules ionised and the stronger the base

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26
Q

How does amine act as lewis base?

A

Amine acts as a base by donating its lone of electrons on N to chemical species with energetically accessible vacant orbitals

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27
Q

Are aliphatic amines or NH3 a stronger base and why?

A
  • Aliphatic amines are stronger bases than ammonia
  • Electron-donating alkyl group makes the lone pair of electrons on N atom of amine more available for donation
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28
Q

In gaseous phase, what is the order of increasing basicity for primary, secondary and tertiary amines

A
  • primary amines < secondary amines < tertiary amines
  • the greater the number of electron-donating alkyl groups, the more available the lone pair of electrons on N for donation
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29
Q

Are phenylamines a stronger or weaker base than NH3 and why?

A
  • Phenylamine is a weaker base than NH3
  • The p orbital of the N atom overlaps with the pi electron cloud of the benzene ring. Lone pair of electrons on N atom of phenylamine is delocalised into the benzene ring, making it less available for donation
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30
Q

How do substituents affect the basicity of amines?

A
  • Electron-donating substituents make the lone pair of electrons on N atom more available for donation, increasing the basicity of amines
  • Electron-withdrawing substituents make the lone pair of electrons on N atom less available for donation, decreasing the basicity of amines
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31
Q

How do amines act as a nucleophile?

A

Amines act as a nucleophile due to the availability of lone pair of electrons on N atom for attacking an electron deficient centre

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32
Q

What are the methods to prepare amines?

A
  1. Reduction of nitriles or amides
  2. Reduction of nitrobenzenes to form phenylamines
  3. Nucleophilic substitution of halogenoalkanes by ammonia
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33
Q

What are the reagents and conditions for the reduction of nitriles to form amines?

A
  • LiAlH4 in dry ether
  • H2, Ni and heat
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34
Q

What is the equation for the reduction of nitriles to form amines?

A

RCN + 4[H] → RCH2NH2

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35
Q

What is the equation for the reduction of amides to form amines?

A

RCONH2 + 4[H] → RCH2NH2 + H2O

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36
Q

What are the reagents and conditions for the reaction of amides to form amines?

A

LiAlH4 in dry ether

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37
Q

What are the reagents and conditions for the reduction of nitrobenzenes to form phenylamines?

A
  1. Sn, conc. HCl, heat
  2. NaOH (aq)
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38
Q

What is the equation of the reduction of nitrobenzenes to form phenylamines?

A

Ar-NO2 + 6[H] → Ar-NH2 + 2H2O

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39
Q

What are the reagents and conditions for the nucleophilic substitution of halogenoalkanes by ammonia?

A

excess NH3, ethanol, heat in sealed tube

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40
Q

What is the equation for the nucleophilic substitution of halogenoalkanes by ammonia?

A

R-X + excess NH3 → R-NH2 + HX

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41
Q

What are the reactions of amines?

A
  1. Acid-Base reaction
  2. Condensation to form amides
  3. Nucleophilic substitution of halogenoalkanes
  4. Electrophilic substitution of phenylamines with Br2 (aq)
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42
Q

What is the equation of the acid-base reaction of aliphatic amines?

A

R-NH2 + HCl → (RNH3)⁺Cl⁻

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43
Q

What is the equation of the acid-base reaction of aromatic amines?

A

Ar-NH2 + HCl → Ar-NH3⁺Cl⁻

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44
Q

What is the reaction for amines forming amides?

A

Condensation

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45
Q

What is the equation of the formation of amides?

A

RNH2 + R’COCl → R’CONHR + HCl

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46
Q

What is the reagents and conditions for the nucleophilic substitution of amines with halogenoalkanes?

A

Excess amine, ethanol, heat under reflux

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47
Q

What is the equation of the nucleophilic substitution of amines with halogenoalkanes?

A

R-NH2 + R’-Cl → R-NH-R’ + HCl

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48
Q

What are the reagents and conditions for the electrophilic substitution of phenylamines?

A

Br2 (aq)
(reaction occurs readily in the cold)

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49
Q

Why can phenylamines undergo electrophilic substitution in the cold and in the absence of halogen carrier catalyst?

A

-NH2 group is electron-donating and activates the ring towards electrophilic substitution

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50
Q

What is the observation for the electrophilic substitution of phenylamines?

A

Orange Br2 (aq) decolourises and white precipitate is formed
(white fumes of HBr may not be formed because HBr dissolved in aqueous medium)

51
Q

What is the general formula for primary amides?

52
Q

What is the general formula for secondary amides?

53
Q

What is the general formula for tertiary amides?

A

RCONR’R’’

54
Q

How to name amides?

A

Replace ‘-oic acid’ by ‘-amide’

55
Q

What are the physical properties of amides like?

A
  • primary and secondary amides have relatively high boiling points and they form dimers in liquid phase due to hydrogen bonds between molecules
  • tertiary amides cannot form hydrogen bonds between their molecules
56
Q

Are amides acidic, basic or neutral and why?

A

Amides are neutral because the p orbital of N atom overlaps with the pi electron cloud of the neighbouring carbonyl (-C=O) group, the lone pair of electrons on N atom is delocalised into the C=O group and hence not available for donation

57
Q

How to prepare amides?

A
  1. Reaction of acyl chlorides with ammonia
  2. Reaction of acyl chlorides with amines
58
Q

What is the type of reaction of the reaction of acyl chlorides with ammonia?

A

Condensation

59
Q

What is the type of reaction of the reaction of acyl chlorides with amines?

A

Condensation

60
Q

What is the equation for the reaction of acyl chlorides and ammonia to prepare amides?

A

RCOCl + NH3 → RCONH2 + HCl

61
Q

What is the equation for the reaction of acyl chlorides and amines to prepare amides?

A

RCOCl + NH2R’ → RCONHR’ + HCl

62
Q

What are the reactions of amides?

A
  1. Acidic Hydrolysis
  2. Alkaline Hydrolysis
  3. Reduction
63
Q

What are the reagents and conditions for acidic hydrolysis of amides?

A

HCl (aq) or H2SO4 (aq), heat under reflux

64
Q

What is the equation for acid hydrolysis of amides?

A

RCONH2 + H2O + H⁺ → RCOOH + NH4⁺

65
Q

What are the reagents and conditions for alkaline hydrolysis of amides?

A

NaOH (aq), heat under reflux

66
Q

What is one method to identify primary amide?

A

Test for NH3 upon heating with NaOH

67
Q

What is the equation for alkaline hydrolysis of amides?

A

RCONH2 + OH⁻ → RCOO⁻ + NH3

68
Q

What are the reagents and conditions for reduction of amides?

A

LiAlH4 in dry ether

69
Q

What is the equation for the reduction of amides?

A

RCONH2 + 4[H] → R-CH2NH2 + H2O

70
Q

What do amino acids contain?

A

It contains at least one amino group (-NH2) and one carboxyl group (-COOH)

71
Q

What is alpha carbon in amino acids?

A

The carbon atom next to -COOH group

72
Q

What is beta carbon in amino acids?

A

The carbon next to the alpha carbon (two carbons away from -COOH)

73
Q

What are alpha amino acids?

A

Amino acids with -NH2 group attached to the alpha carbon

74
Q

What is the general formula for alpha amino acids?

A

H2NCHRCOOH

75
Q

How are zwitterions formed?

A

An amino acid undergoes intramolecular acid-base reaction where the basic ammonia group (-NH2) accepts a proton to become (-NH₃⁺) while the acidic carboxyl group (-COOH) loses a proton to become (-COO⁻)

76
Q

What is the formula/structure of a zwitterion?

A

H3N⁺CHRCOO⁻

77
Q

What do the physical properties of amino acids resemble and why?

A

Ionic compounds because amino acids exist as zwitterions in aqueous and solid state

78
Q

How can amino acids be classified?

A

Depending on the nature of R group, amino acids can be classified as
1. Non-polar or polar
- non-polar: R group cannot form effective interactions with water molecules
- polar: R group can form effective interactions such as hydrogen bonds with water molecules
2. Acidic, Basic or Neutral

79
Q

Do amino acids exhibit enantiomerism?

A

All amino acids except glycine (R group is H) are chiral

80
Q

What are the melting points of amino acids like and why?

A

Amino acids are crystalline solids with high melting points because a large amount of energy is required to overcome the strong electrostatic forces of attraction between oppositely charged groups of the zwitterions

81
Q

Are amino acids soluble in water and why?

A

Amino acids are soluble in water but insoluble in non-polar solvents because zwitterions forms ion-dipole interactions with water molecules

82
Q

What is the nature of amino acids?

A

Amino acids are amphoteric
- In acidic solutions (low pH), an amino acids behaves as a base and accepts a proton from the acid to form a cation
- In basic solution (high pH), an amino acids behaves as an acid and donates a proton to the base to form an anion

83
Q

What is the equation of amino acids in low pH?

A

H₃N⁺CHRCOO⁻ + H⁺ → H₃N⁺CHRCOOH

84
Q

What is the equation of amino acids in high pH?

A

H₃N⁺CHRCOO⁻ + OH⁻ → H₂NCHRCOO⁻ + H₂O

85
Q

What is the structure and charge of amino acids in aqueous solutions determined by?

A

[H⁺], which is given by the pH of the solution

86
Q

How can the charge of the groups of amino acids be predicted if pKa is known?

A
  • If pH of the solution is smaller than pKa of the group by 1 or more units, the protonated form of the group (eg. -COOH or -NH₃⁺) will be predominant
  • If pH of the solution is larger than pKa of the group by 1 or more units, the deprotonated form of the group (eg. -COO⁻ or -NH2) will be predominant
87
Q

What happens when a potential difference is applied to a zwitterion in its protonated form?

A

The cation will migrate towards the negative electrode (cathode)

88
Q

What happens when a potential difference is applied to a zwitterion in its deprotonated form?

A

The anion will migrate towards the positive electrode (anode)

89
Q

What is an isoelectric point?

A

-particular pH at which amino acids exists solely in its zwitterionic form with a net charge of zero
-at this pH, the amino acid will not migrate under the influence of an electric field

90
Q

What happens at a pH well below amino acids’ isoelectric point?

A

The amino acid will exist predominantly as a cation

91
Q

What happens at a pH well above amino acids’ isoelectric point?

A

The amino acid will exist predominantly as an anion

92
Q

What is the formula for calculating isoelectric point?

A

Calculate average pKa for both groups

93
Q

How does amino acid act as a buffer?

A

When a small amount of acid is added,
H₃N⁺CHRCOO⁻ + H⁺ → H₃N⁺CHRCOOH
When a small amount of alkali is added,
H₃N⁺CHRCOO⁻ + OH⁻ → H₂NCHRCOO⁻ + H₂O

94
Q

What is the explanation for the zwitterion form of aspartic acid?

A

-COOH on alpha carbon is more acidic than -COOH in the R group
- electron withdrawing N is nearer which helps to disperse the negative charge on -COO⁻ group more effectively
- thus, -COO⁻ on alpha carbon is more stable

95
Q

What are the reactions of amino acids?

A
  1. Acid-base reaction with acids or bases
  2. Acid-carbonates reaction with carbonates
  3. Condensation reaction forming amides
  4. Condensation reaction forming esters
96
Q

What is the equation of amino acids with acids, eg. HCl?

A

H₂NCHRCOOH + HCl → [H₃N⁺CHRCOOH]Cl⁻

97
Q

What is the equation of amino acids with bases, eg. NaOH?

A

H₂NCHRCOOH + NaOH → [H₂NCHRCOO⁻Na⁺] + H₂O

98
Q

What is the equation of amino acids with carbonates?

A

2H₂NCHRCOOH + Na₂CO₃ → 2[H₂NCHRCOO⁻Na⁺] + CO₂ + H₂O

99
Q

What is the equation of condensation reaction of amino acids to form amides?

A

RCOCl + H₂NCHRCOOH → RCONHCHRCOOH + HCl

100
Q

What are the reagents and conditions for amino acid condensation reaction to form esters?

A

a few drops of conc. H2SO4, heat under reflux

101
Q

What is the equation of condensation reaction of amino acids to form esters?

A

H₂NCHRCOOH + R’-OH → H₂NCHRCOOR’ + H₂O

102
Q

What is the relationship between amino acids and proteins?

A

Amino acids are the basic building units of proteins, up to thousands of amino acids may make up one protein molecule

103
Q

How to synthesize a protein molecule?

A

The synthesis of protein molecule involves the formation of peptide bonds via condensation reaction between carboxyl group of one amino acid and amino group of another amino acid, a molecule of water is removed

104
Q

What is a peptide bond/linkage?

105
Q

What is a dipeptide?

A
  • two amino acids joined by a peptide bond/linkage (-CONH-)
  • dipeptide possess a free amino acid on one side and free carboxyl group on the other
106
Q

What is N-terminus?

A

Free amino group

107
Q

What is C-terminus?

A

Free carboxyl group

108
Q

How many amino acids is tripeptide made from and how many peptide bonds does it have?

A

Three amino acids and two peptide bonds

109
Q

How many amino acids is tetrapeptide made from and how many peptide bonds does it have?

A

Four amino acids and contains three peptide bonds

110
Q

What is a polypeptide?

A

Peptide of a longer chain length

111
Q

What is an amino acid in a peptide/polypeptide chain called?

A

Amino acid residue

112
Q

What are proteins made up of?

A

One or more polypeptides

113
Q

What does a polypeptide backbone consist of?

A

Repeating units of “-NHCHCO-“

114
Q

What are the side chains of the polypeptides?

A

R group of amino acid residues

115
Q

By convention, how is he sequence of amino acid residues in a polypeptide chain written?

A

N-terminus is on the left and C-terminus in on the right

116
Q

What are the reactions of polypeptides and proteins?

A
  1. Acidic hydrolysis
  2. Alkaline Hydrolysis
  3. Enzymatic Hydrolysis (cannot suggest at chemical method)
117
Q

What are the reagents and conditions for acidic hydrolysis of polypeptides and proteins?

A

HCl (aq) or H2SO4 (aq), heat for several hours

118
Q

What is the equation of acidic hydrolysis of polypeptides and proteins?

A

—CHRCONHCHR— → —CHRCOOH + H₃N⁺HCR—

119
Q

What are the reagents and conditions for alkaline hydrolysis of polypeptides and proteins?

A

NaOH(aq), heat for several hours

120
Q

What is the equation for alkaline hydrolysis of polypeptides and proteins?

A

—CHRCONHCHR— → —CHRCOO⁻ + H₂NHCR—

121
Q

What is the equation of enzymatic hydrolysis of polypeptides and proteins?

A

—CHRCONHCHR— → —CHRCOOH + H₂NHCR—

122
Q

What are the reagents and conditions for acid-base reaction of amines?

A

HCl (or any acid)

123
Q

What are the reagents and conditions for amine undergoing condensation to form amides?

A

Acyl chloride (RCOCl)

124
Q

Why is RCOCl + NH3 a condensation reaction?

A

Condensation: addition-elimination reaction
Addition: NH3 add across C=O bond
Elimination: HCl molecule eliminated

Chemistry (21 decks)

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