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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Derivatives of NH3 where one of more of the hydrogen atoms in of the ammonia molecule has been replaced by alkyl or aryl group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
What does a larger Kb value mean?
The larger the Kb value, the greater the proportion of amine molecules ionised and the stronger the base
26
How does amine act as lewis base?
Amine acts as a base by donating its lone of electrons on N to chemical species with energetically accessible vacant orbitals
27
Are aliphatic amines or NH3 a stronger base and why?
- 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
28
In gaseous phase, what is the order of increasing basicity for primary, secondary and tertiary amines
- 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
29
Are phenylamines a stronger or weaker base than NH3 and why?
- 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
30
How do substituents affect the basicity of amines?
- 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
31
How do amines act as a nucleophile?
Amines act as a nucleophile due to the availability of lone pair of electrons on N atom for attacking an electron deficient centre
32
What are the methods to prepare amines?
1. Reduction of nitriles or amides 2. Reduction of nitrobenzenes to form phenylamines 3. Nucleophilic substitution of halogenoalkanes by ammonia
33
What are the reagents and conditions for the reduction of nitriles to form amines?
- LiAlH4 in dry ether - H2, Ni and heat
34
What is the equation for the reduction of nitriles to form amines?
RCN + 4[H] → RCH2NH2
35
What is the equation for the reduction of amides to form amines?
RCONH2 + 4[H] → RCH2NH2 + H2O
36
What are the reagents and conditions for the reaction of amides to form amines?
LiAlH4 in dry ether
37
What are the reagents and conditions for the reduction of nitrobenzenes to form phenylamines?
1. Sn, conc. HCl, heat 2. NaOH (aq)
38
What is the equation of the reduction of nitrobenzenes to form phenylamines?
Ar-NO2 + 6[H] → Ar-NH2 + 2H2O
39
What are the reagents and conditions for the nucleophilic substitution of halogenoalkanes by ammonia?
excess NH3, ethanol, heat in sealed tube
40
What is the equation for the nucleophilic substitution of halogenoalkanes by ammonia?
R-X + excess NH3 → R-NH2 + HX
41
What are the reactions of amines?
1. Acid-Base reaction 2. Condensation to form amides 3. Nucleophilic substitution of halogenoalkanes 4. Electrophilic substitution of phenylamines with Br2 (aq)
42
What is the equation of the acid-base reaction of aliphatic amines?
R-NH2 + HCl → (RNH3)⁺Cl⁻
43
What is the equation of the acid-base reaction of aromatic amines?
Ar-NH2 + HCl → Ar-NH3⁺Cl⁻
44
What is the reaction for amines forming amides?
Condensation
45
What is the equation of the formation of amides?
RNH2 + R'COCl → R'CONHR + HCl
46
What is the reagents and conditions for the nucleophilic substitution of amines with halogenoalkanes?
Excess amine, ethanol, heat under reflux
47
What is the equation of the nucleophilic substitution of amines with halogenoalkanes?
R-NH2 + R'-Cl → R-NH-R' + HCl
48
What are the reagents and conditions for the electrophilic substitution of phenylamines?
Br2 (aq) (reaction occurs readily in the cold)
49
Why can phenylamines undergo electrophilic substitution in the cold and in the absence of halogen carrier catalyst?
-NH2 group is electron-donating and activates the ring towards electrophilic substitution
50
What is the observation for the electrophilic substitution of phenylamines?
Orange Br2 (aq) decolourises and white precipitate is formed (white fumes of HBr may not be formed because HBr dissolved in aqueous medium)
51
What is the general formula for primary amides?
RCONH2
52
What is the general formula for secondary amides?
RCONHR'
53
What is the general formula for tertiary amides?
RCONR'R''
54
How to name amides?
Replace '-oic acid' by '-amide'
55
What are the physical properties of amides like?
- 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
Are amides acidic, basic or neutral and why?
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
How to prepare amides?
1. Reaction of acyl chlorides with ammonia 2. Reaction of acyl chlorides with amines
58
What is the type of reaction of the reaction of acyl chlorides with ammonia?
Condensation
59
What is the type of reaction of the reaction of acyl chlorides with amines?
Condensation
60
What is the equation for the reaction of acyl chlorides and ammonia to prepare amides?
RCOCl + NH3 → RCONH2 + HCl
61
What is the equation for the reaction of acyl chlorides and amines to prepare amides?
RCOCl + NH2R' → RCONHR' + HCl
62
What are the reactions of amides?
1. Acidic Hydrolysis 2. Alkaline Hydrolysis 3. Reduction
63
What are the reagents and conditions for acidic hydrolysis of amides?
HCl (aq) or H2SO4 (aq), heat under reflux
64
What is the equation for acid hydrolysis of amides?
RCONH2 + H2O + H⁺ → RCOOH + NH4⁺
65
What are the reagents and conditions for alkaline hydrolysis of amides?
NaOH (aq), heat under reflux
66
What is one method to identify primary amide?
Test for NH3 upon heating with NaOH
67
What is the equation for alkaline hydrolysis of amides?
RCONH2 + OH⁻ → RCOO⁻ + NH3
68
What are the reagents and conditions for reduction of amides?
LiAlH4 in dry ether
69
What is the equation for the reduction of amides?
RCONH2 + 4[H] → R-CH2NH2 + H2O
70
What do amino acids contain?
It contains at least one amino group (-NH2) and one carboxyl group (-COOH)
71
What is alpha carbon in amino acids?
The carbon atom next to -COOH group
72
What is beta carbon in amino acids?
The carbon next to the alpha carbon (two carbons away from -COOH)
73
What are alpha amino acids?
Amino acids with -NH2 group attached to the alpha carbon
74
What is the general formula for alpha amino acids?
H2NCHRCOOH
75
How are zwitterions formed?
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
What is the formula/structure of a zwitterion?
H3N⁺CHRCOO⁻
77
What do the physical properties of amino acids resemble and why?
Ionic compounds because amino acids exist as zwitterions in aqueous and solid state
78
How can amino acids be classified?
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
Do amino acids exhibit enantiomerism?
All amino acids except glycine (R group is H) are chiral
80
What are the melting points of amino acids like and why?
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
Are amino acids soluble in water and why?
Amino acids are soluble in water but insoluble in non-polar solvents because zwitterions forms ion-dipole interactions with water molecules
82
What is the nature of amino acids?
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
What is the equation of amino acids in low pH?
H₃N⁺CHRCOO⁻ + H⁺ → H₃N⁺CHRCOOH
84
What is the equation of amino acids in high pH?
H₃N⁺CHRCOO⁻ + OH⁻ → H₂NCHRCOO⁻ + H₂O
85
What is the structure and charge of amino acids in aqueous solutions determined by?
[H⁺], which is given by the pH of the solution
86
How can the charge of the groups of amino acids be predicted if pKa is known?
- 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
What happens when a potential difference is applied to a zwitterion in its protonated form?
The cation will migrate towards the negative electrode (cathode)
88
What happens when a potential difference is applied to a zwitterion in its deprotonated form?
The anion will migrate towards the positive electrode (anode)
89
What is an isoelectric point?
-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
What happens at a pH well below amino acids' isoelectric point?
The amino acid will exist predominantly as a cation
91
What happens at a pH well above amino acids' isoelectric point?
The amino acid will exist predominantly as an anion
92
What is the formula for calculating isoelectric point?
Calculate average pKa for both groups
93
How does amino acid act as a buffer?
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
What is the explanation for the zwitterion form of aspartic acid?
-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
What are the reactions of amino acids?
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
What is the equation of amino acids with acids, eg. HCl?
H₂NCHRCOOH + HCl → [H₃N⁺CHRCOOH]Cl⁻
97
What is the equation of amino acids with bases, eg. NaOH?
H₂NCHRCOOH + NaOH → [H₂NCHRCOO⁻Na⁺] + H₂O
98
What is the equation of amino acids with carbonates?
2H₂NCHRCOOH + Na₂CO₃ → 2[H₂NCHRCOO⁻Na⁺] + CO₂ + H₂O
99
What is the equation of condensation reaction of amino acids to form amides?
RCOCl + H₂NCHRCOOH → RCONHCHRCOOH + HCl
100
What are the reagents and conditions for amino acid condensation reaction to form esters?
a few drops of conc. H2SO4, heat under reflux
101
What is the equation of condensation reaction of amino acids to form esters?
H₂NCHRCOOH + R'-OH → H₂NCHRCOOR' + H₂O
102
What is the relationship between amino acids and proteins?
Amino acids are the basic building units of proteins, up to thousands of amino acids may make up one protein molecule
103
How to synthesize a protein molecule?
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
What is a peptide bond/linkage?
-CONH-
105
What is a dipeptide?
- 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
What is N-terminus?
Free amino group
107
What is C-terminus?
Free carboxyl group
108
How many amino acids is tripeptide made from and how many peptide bonds does it have?
Three amino acids and two peptide bonds
109
How many amino acids is tetrapeptide made from and how many peptide bonds does it have?
Four amino acids and contains three peptide bonds
110
What is a polypeptide?
Peptide of a longer chain length
111
What is an amino acid in a peptide/polypeptide chain called?
Amino acid residue
112
What are proteins made up of?
One or more polypeptides
113
What does a polypeptide backbone consist of?
Repeating units of "-NHCHCO-"
114
What are the side chains of the polypeptides?
R group of amino acid residues
115
By convention, how is he sequence of amino acid residues in a polypeptide chain written?
N-terminus is on the left and C-terminus in on the right
116
What are the reactions of polypeptides and proteins?
1. Acidic hydrolysis 2. Alkaline Hydrolysis 3. Enzymatic Hydrolysis (cannot suggest at chemical method)
117
What are the reagents and conditions for acidic hydrolysis of polypeptides and proteins?
HCl (aq) or H2SO4 (aq), heat for several hours
118
What is the equation of acidic hydrolysis of polypeptides and proteins?
---CHRCONHCHR--- → ---CHRCOOH + H₃N⁺HCR---
119
What are the reagents and conditions for alkaline hydrolysis of polypeptides and proteins?
NaOH(aq), heat for several hours
120
What is the equation for alkaline hydrolysis of polypeptides and proteins?
---CHRCONHCHR--- → ---CHRCOO⁻ + H₂NHCR---
121
What is the equation of enzymatic hydrolysis of polypeptides and proteins?
---CHRCONHCHR--- → ---CHRCOOH + H₂NHCR---
122
What are the reagents and conditions for acid-base reaction of amines?
HCl (or any acid)
123
What are the reagents and conditions for amine undergoing condensation to form amides?
Acyl chloride (RCOCl)
124
Why is RCOCl + NH3 a condensation reaction?
Condensation: addition-elimination reaction Addition: NH3 add across C=O bond Elimination: HCl molecule eliminated

Chemistry (21 decks)

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