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La Chimie H2 > Nitrogen Compounds > Flashcards

Nitrogen Compounds Flashcards

1
Q

Amines may be classified as…?

A

primary, secondary, tertiary,
depending on no. of alkyl/aryl grp attached to N atom
(primary is 1 R grp, tertiary is 3 R grp)

NOTE: quaternary ammonium ion is organic equivalent of NH4+ ion where 4 alkyl/aryl grp hv replaced H atoms

  • oso can b classified aliphatic, aromatic
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2
Q

Describe nomenclature of amines

A

aliphatic
- named by specifying alkyl grp attached to N atom, follow by suffix amine
eg
methylamine (1 deg), phenylmethylamine (1 deg), diethylamine (2 deg)

aromatic
- N atom directly attach to benzene ring
- named as derivatives of simplest aromatic amine (phenylamine)
eg
phenylamine (simplest), 4-methylphenylamine, N-methylphenylamine

  • in compounds where amine grp is named as substituent, prefix amino- is used
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3
Q

Explain boiling point of amines

A
  1. Within homologous series, bp generally increase w increasing e- cloud size (seen by increasing Mr)
    bcos
    - w increasing Mr, size & polarisability of e- cloud increase
    => increasing strength/extent of intermolecular id-id attract n, require more energy to overcome
  2. for isomeric amines bp tend follow 3 deg < 2 deg < 1 deg
    bcos
    - more energy needed overcome stronger intermolecular H bonding in primary, secondary amines vs weaker intermolecular pd-pd attract n of tertiary amine
    => tertiary amine hv lowest bp
    - primary vs secondary: presence of more alkyl grp bonded to N in secondary amine cause steric effect, decreases availability of lp of e- on N for intermolecular H bonding. Secondary amine hv weaker intermolecular H bonding, needs less energy overcome
    => secondary amine hv lower bp than primary amine
  3. Amines hv higher bp than hydrocarbons of similar e- cloud size
    bcos,
    - more energy needed to overcome stronger intermolecular H bonding in amines vs weaker intermolecular id-id attract n for hydrocarbon
  4. Amines hv lower bp than alcohols of similar Mr
    bcos,
    - N-H bond less polar than O-H bond, intermolecular H bond in amines weaker, need less energy overcome than those in alcohols
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4
Q

Explain solubility of amines in water

A
  1. Amines w small molecular size soluble in water
    bcos,
    - amines can form H bond w water molecules
    - energy released by form n H bond btw amine, H2O molecules enough overcome intermolecular H bond btw H2O & amine molecules respectively
  2. Amines w larger molecular size less soluble in water
    bcos,
    - as alkyl/aryl (R) grp(s) bcome bulkier/larger, solubility in water decrease as greater hydrophobic nature of R grp decrease strength of interact n btw amine & water
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5
Q

Name reagent, conditions and type of reaction of nitriles + H

A

R&C:
1. LiAlH4 in dry ether
or
2. H2 w Ni catalyst, high temp & Pa
or
3. H2 w Pd/Pt catalyst

type: reduct n

NOTE:
-CN –> -CH2NH2 (forms primary smine)

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6
Q

Name reagent, conditions and type of reaction of amides + H

A

R&C: LiAlH4 in dry ether
type: reduct n

NOTE: H2(g), NaBH4 cnt b used reduce amides,
this rxn forms primary amine

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7
Q

Name reagent, conditions and type of reaction of halogenoalkane and NH3

A

R&C: excess conc NH3 in ethanol, heat in sealed tube
type: Nu Sub

NOTE:
- forms primary amine
- use of excess NH3 discourage form n of side-pdt, give primary amine as MAIN pdt
- if excess of RX is used, main pdt formed is quaternary ammonium salt

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8
Q

Name reagent, conditions and type of reaction of nitrobenzene and H

A

R&C:
Sn in excess conc HCl, heat (reduct n),
followed by add n NaOH(aq) (neutral n)

type: reduct n

NOTE:
- other reducing agent cnt b used
- pdt formed in 1st step is C6H5NH3+Cl-
- NaOH(aq) added in 2nd step for acid-base rxn w acidic C6H5NH3+Cl to form required pdt, C6H5NH2
- Oni method to prepare phenylamine in syllabus

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9
Q

In aqueous state, amine behaves as … Thus, any process that … availability of … for bonding with a proton will cause amine to be a …

A

Bronsted-Lowry base,
increases,
lone pair of electrons,
stronger base

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10
Q

Explain relative basicity of ammonia, ethylamine and phenylamine

A

order of base strength:
ethylamine > ammonia > phenylamine

ethylamine stronger than ammonia bcos
- e-donating ethyl grp increase e- density of lp of e- on N atom
=> lp e- more available to accept proton (form dative bond w H+)
- ammonia no e-donating grp attached to N atom, so lp e- on N less available accept proton

phenylamine weaker base than ammonia bcos
- in phenylamine, lp e- on N atom delocalised into benzene ring
=> lp e- less available to accept proton
- lp e- on N in ammonia not delocalised so more available to accept proton

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11
Q

Describe effects of substituents on basicity

A
  1. e-donate grp cause increase in basicity
    Bcos,
    - increase e-density of lp e- on N atom
    - lp more available accept H+ ion
    - stronger base
  2. e-withdraw grp cause decrease in basicity
    Bcos,
    - decrease e-density of lp e- on N atom
    - lp less available to accept H+ ion
    - weaker base

Generally,
- more grp —> greater effect
- effect decrease w dist fr N atom

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12
Q

Describe basicity of amines in gaseous phase

A
  • amine behave as Lewis base
  • N atom use its lp e- form dative bond w e-deficient species
    => any process increasing availability of lp e- for bonding w proton cause amine bcome stronger base

NOTE:
In gaseous phase, no water molecules to interact w amine molecules so discuss n amines as Bronsted Lowry base not considered

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13
Q

Explain relative basicity of primary, secondary and tertiary aliphatic amines in gaseous phase

A

Basicity: tertiary>secondary>primary

Order of base strength:
Trimethylamine>dimethylamine>methylamine
Bcos,
- from methylamine to trimethylamine, increase in no of e-donate alkyl grp increases e-density of lp e- on N atom
=> lp more available form dative bond to e-deficient species

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14
Q

Name reagent, conditions and type of reaction of amines and acid

A

R&C: HCl(aq)/H2SO4(aq) or any aq acid, r.t.p.
Type: neutral n

Note:
Forms salts

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15
Q

Name reagent, conditions and type of reaction of amines and acyl chloride

A

R&C: anhydrous acyl chloride
Type: condensat n

Note:
- cnt use RCOOH as neutral n occur instead
- ONLY method form amides

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16
Q

Name reagent, conditions, type of reaction, OBSERVATION and APPLICATION of phenylamine and Br2

A

R&C: Br2(aq)
Type: e- sub
Observ n: decolour n orange Br2(aq) sol n w form n white ppt
Application: chemical test for phenylamine (NOTE: phenol give similar observ n)

17
Q

As compared to electrophilic substitution of benzene, conditions required for that of phenylamine are considered mild (ie rtp, no catalyst). Why?

A
  • in phenylamine, lp e- on N atom delocalised into benzene ring
    => increased e- density in ring makes it more readily attacked by e-philes (activated towards e- sub)
18
Q

What are amides?

A
  • derivatives of RCOOH containing structural unit - O= C-N- -
19
Q

Describe nomenclature of amides

A
  • generally named by replace ‘e’ of alkanes w ‘-amide’
    eg ethanamide
  • C atom of -CONH2 is NUMBERED 1
  • substituent grp bonded to N given prefix N-
    eg N-methylpentanamide
20
Q

Explain boiling and melting point of amides

A
  • RCONH2 and RCONHR’ amides can form intermolecular H bond due to presence of N-H bond
    =>expected to have higher mp/bp than RCONR’R’’ amides
  • RCONR’R’’ amides NO H bond due to absence of H atom bonded to N
21
Q

Explain solubility of amides in water

A
  • amide can form H bond w water molecules
    => expect smaller amides to be soluble in water
  • larger amides tend hv larger hydrophobic section, cause decreased solubility (id-id)
22
Q

Explain lack of basicity of amides

A

Amides are NEUTRAL (not basic, neutral to litmus)
Bcos
- lp e- on N atom delocalised w adjacent C=O thereby reduce e-density on N atom
=> N atom less available accept/ form dative bond to proton (H+)

23
Q

Name reagent, condition and type of reaction of acyl chloride and NH3 / amine

A

R&C:
1. To form RCO2NH2 :
RCOCl w NH3, rtp (readily react)

  1. To form RCO2NHR’ :
    ROCl w primary amine
  2. To form RCO2NHR’R’’ :
    ROCl w secondary amine

Type: condensat n

24
Q

Describe overview of hydrolysis of amides

A
  • (adding H2O) involve cleavage of C-N bond in amide
  • forms carboxylic acid & ammonia/amine
  • in basic medium, acid salt forms (from RCOOH)
  • in acidic medium, NH4+/ amine salt forms
25
Q

Name reagent, condition and type of reaction of amide and acid

A

R&C: HCl(aq)/H2SO4(aq), heat under reflux
Type: acidic hydrolysis

26
Q

Name reagent, condition and type of reaction of amide and base

A

R&C: NaOH(aq)/KOH(aq), heat under reflux
Type: basic hydrolysis

NOTE: in any rxn where ammonia forms, this can be used to test presence of RCONH2

27
Q

Name reagent, condition and type of reaction of amides + H

A

R&C: LiAlH4 in dry ether
Type: reduct n

Note:
Cnt use H2 (g) or NaBH4

28
Q

Describe some reagent and conditions to distinguish RCONH2, ammonium salts and amines

A
  1. NaOH(aq), heat
    - to distinguish RCONH2 amides fr other organic cpds
    - Observ n: pungent NH3 gas evolved turned moist red litmus paper blue
    NOTE:
    ammonium salts oso liberate NH3(g) on warming w NaOH (see Data Booklet QA for Cation tests)
  2. Br2(aq)
    - distinguish Phenylamine fr other cpd (except phenol)
    - Observ n: orange Br2(aq) decolourise w form n white ppt
  3. Dilute acid (eg HCl aq)
    - distinguish Amines insoluble in water fr other insoluble organic cpd
    - observ n: amine insoluble in water but SOLUBLE in dilute acid give homogenous sol n
    (Bcos Amine react in neutral n rxn form ionic salt soluble in water due to form n strong ion-dipole interact n btw ion & water)
29
Q

What is amino acid? How about a α-amino acid? Give general formula

A
  • amino acid contain >= 1 -COOH & 1 amino grp (-NH2)
  • α-amino acid is an amino acid where both -NH2 & -COOH grp r direct bonded to same C atom (α-carbon)
  • general formula of α-amino acid is

H2N- H-C-R -COOH

30
Q

Describe nomenclature of amino acid

A
  • named as derivatives of RCOOH
    eg
    2-aminoethanoic acid (glycine),
    2-amino-3methylbutanoic acid (valine)
31
Q

Define zwitterion

A
  • Amino acid exist predominantly as electrically neutral dipolar ion (zwitterion)
32
Q

Describe physical properties of amino acids

A
  1. Exist as crystalline solids w high mp (> 200 deg C)
    Bcos
    - large amt energy needed overcome strong e-static force attract n btw zwitterion
  2. Soluble in water
    Bcos
    - ion-dipole interact n (similar to ionic cpd) formed w water molecules cause release of sufficient energy, cause detachment of zwitterion fr crystal lattice for solvat n
33
Q

Describe neutralisation reactions of amino acids

A
  • zwitterion hv amphoteric nature as undergo neutral n at respective -COO- or -NH3+ grp
  • as acid: -NH3+ grp responsible for acidic properties (reversible rxn)
  • as base: -COO- grp responsible for basic properties (reversible rxn)
34
Q

Describe amino acid zwitterion in aqueous solution

A
  • can act as buffer sol n
  1. on add n small amt H+,
    - added H+ removed
    => [H+] slightly changed so pH fairly constant
  2. On add n small amt OH-
    - added OH- removed
    => [OH-] slightly changed so pH fairly constant
35
Q

Describe behaviour of amino acids in solutions of different pH

A
  • can exist in diff form depending on pH of sol n
  • fr low to high pH, can exist as cationic (fully protonated) to (electrically) neutral to anionic
  • fully protonated form is acidic in nature & can b titrated w base
36
Q

How to approach questions dealing with amino acids and multiple pKa values?

A
  1. Assign pKa values to each acidic/basic grp
    - relevant to groups in protonated form (eg for -NH2, pKa value refer to that of -NH3+)
    - if got 2 identical grp, infer which hv lower pKa value (stronger acid)
    Eg. W 2 -COOH grp, the one nearer to -NH2 hv lower pKa value as it is stronger acid (bcos -NH2 is e-withdraw grp)
  2. For each grp, compare pH of sol n w its pKa to determine form of gro at that pH
    - if pH of sol n < pKa, grp is protonated (eg -COOH/ -NH3+)
    - if pH of soo n > pKa, grp is deprotonated (eg -COO-/ -NH2)
37
Q

How are peptide linkages formed? Describe

A

By condensat n rxn of amino acids w other amino acid molecules

Resultant molecule aka peptide, each amino acid unit within peptide aka amino acid residue

Warning:
Form n peptide bonds occur in nature under SPECIFIC condit n. Peptide bond CANNOT b formed in lab by simply reacting amine & -COOH grp (bcos in lab, undergo neutral n)

38
Q

Describe peptides

A
  • contains 2 or more α-amino acids linked by peptide bonds
    => 2 amino acids joined tgt: dipeptide (contain 1 peptide bond)
    => 3 amino acids joined tgt: tripeptide (contain 2 peptide bond)
    => many amino acids joined tgt: poly peptide
  • polypeptide containing > 400 amino acid residue r termed proteins
  • protein can contain up to 400 amino acid residue. Diff protein contain diff sequence of amino acid residue
39
Q

Name reagent, condition for complete hydrolysis of proteins

A

R&C:
[acidic] HCl(aq)/H2SO4(aq) or [basic] NaOH(aq), prolonged heat under reflux

NOTE:
- acidic hydrolysis form RCOOH + amine salt
- basic hydrolysis form RCOO- + amine

La Chimie H2 (25 decks)

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