PL lnop: Amines, amides, acyl chlorides, nylons

Question 1

What are amines?

Answer 1

Ammonia where at least one hydrogen is substituted for an alkyl group.

Question 2

• Name the following molecules:
  
  • CH₃NH₂
  • C₂H₅NH_2​
  • CH₃CH₂CH₂NH₂
• _​What type of molecule are they?

Answer 2

• Methylamine
• Ethylamine
• 1-aminopropane/propylamine
• Primary amines

Question 3

• Name CH₃CH(NH₂)CH₃
• What type of molecule is it?

Answer 3

• 2-aminopropane / methyl ethylamine
• Primary amine

Question 4

• Name CH₃NHCH₃
• What type of molecule is it?

Answer 4

• Dimethylamine
• Secondary amine (2 Hs replaced by alkyl groups)

Question 5

• Name CH₃N(CH₃)CH₃
• What type of molecule is it?

Answer 5

• Trimethylamine
• Tertiary amine (3 Hs replaced by alkyl groups)

Question 6

• Name NH₂CH₂NH₂
• What type of molecule is it?

Answer 6

• Methanediamine
• Diamine

Question 7

• Name the following molecules:
  
  • NH₂CH₂CH₂NH₂
  • NH₂CH₂CH₂CH₂CH₂CH₂CH₂NH₂
• What type of molecule are they both?

Answer 7

• Ethanediamine
• 1,6-diamino-hexane
• Diamines

Question 8

Why do amines have the following properties?

• Soluble in water
• Act as bases

Answer 8

• Nitrogen atom has a lone pair of electrons
• So amines can engage in hydrogen bonding with water
• Lone pair accepts H⁺, forming a dative covalent bond

Bonding around N similar to that of ammonia

Question 9

Explain why amines with longer alkyl groups are less soluble in water.

Answer 9

​(For larger alkyl groups:)

Enthalpy change of breaking water-water hydrogen bonds >

enthalpy change of forming intermolecular forces between alkyl group + water

and hydrogen bonds between water + lone pair on N

Question 10

Give the equation for the reaction between 2-aminopropane and water.

Answer 10

CH₃CH(NH₂)CH₃ + H₂O → CH₃CH(NH₃⁺)CH₃ + OH^-

Amines act as H⁺ acceptors

Question 11

Explain why amines react more strongly with acids than with water.

Answer 11

• Lone pair on N partakes in dative covalent bonding, accepting a H⁺ (acting as a base)
• H₃O⁺ ions are more powerful proton donors than water

Question 12

Write the equation for the reaction of 2-aminopropane and hydrochloric acid.

Answer 12

CH₃CH(NH₂)CH₃ + HCl → CH₃CH(NH₃⁺Cl^-)CH₃

Question 13

Write the symbol and word equation for the reaction of ethylamine with an acid.

Answer 13

CH₃CH₂NH_{2 (aq)} + H₃O⁺_(aq) → CH₃CH₂NH₃⁺_(aq) + H₂O_(l)

Ethylamine + hydronium ion → ethylammonium ion + water

Question 14

• What are primary amides?
• Give their general formula
• Draw their general structural formula

Answer 14

• Carboxylic acid derivatives where the OH group is substituted by NH₂
• RCONH₂

Question 15

• How do you name primary amides?
• Name CH₃CONH₂

Answer 15

• Replace the “e” on the end of the alkane with “amide”
• Ethanamide

Question 16

• What are secondary amides?
• Give their general formula
• Draw their general structural formula

Answer 16

• Carboxylic acid derivatives where the OH group is replaced by NHR’
• RCONHR’

Question 17

• How do you name secondary amides?
• Name CH₃CONHCH₃

Answer 17

• RCONH₂R’
• Name in format: N-R’ Ramide, i.e. N-_yl _amide
• N-methyl ethanamide

Question 18

What are acyl chlorides?

Give their general formula.

Answer 18

Carboxylic acid derivatives where the OH is substituted for chlorine.

RCOCl or C_nH_2n+1COCl

Question 19

Name this molecule.

Answer 19

Ethanoyl chloride

Question 20

Name this molecule:

CH₃CH₂CH₂COCl

Answer 20

Butanoyl chloride

Question 21

All of the reactions below occur via the same mechanism. Using an amine and acyl chloride, draw the mechanism. State what it is called.

• Amines + acyl chlorides
• Amides + acyl chlorides
• Alcohols + acyl chlorides
• Carboxylic acids + acyl chlorides
• Condensation polymerisation, forming:
  
  • Polyesters
  • Polyamides (nylons)
  • Polypeptides

Answer 21

Could include intermediate step in which H donates pair of electrons to N⁺ in NH₃, so that it then deprotonates

Question 22

Write an equation for the reaction between 2-aminopropane and ethanoyl chloride.

Answer 22

Draw: nucleophilic substitution

CH₃CH(NH₂)CH₃ + CH₃COCl → CH₃CONH(CH₃)₂ + HCl

Question 23

Suggest and explain which of amines and amides react with acyl chlorides.

Answer 23

• Would react by nuc attack of δ+ carbon in acyl chloride
• Amines react. Amides do not because C=O group pulls e^- away, making them poorer nucleophiles

Question 24

• What type of molecule is formed when acyl chlorides react with amines?
• What mechanism occurs?
• What type of reaction occurs?

Answer 24

• Secondary amide
• Nucleophilic substitution
• Condensation reaction

Question 25

Acyl chlorides react vigorously with alcohols. * What type of mechanism occurs? * What is produced? * What type of reaction occurs?

Answer 25

* Nucleophilic substitution * Esters (RCOCl + R'OH → RCOOR' + HCl) * Condensation reaction

Question 26

* What are polyamides? * What is the other name for them?

Answer 26

* Polymers where monomer links are secondary amide groups * Nylons

Question 27

* In what 2 ways can polyamides be made? * Which method is quicker?

Answer 27

* Diamine + either dicarboxylic acid or diacyl dichloride * Diacyl chlorides react more quickly because Cl^- is stabler in solution than OH^-, so is better leaving group ## Footnote * Diacyl dichloride = symmetrical molecules where both ends are COCl* * Stability in solution: Cl^- ions \> carboxylate ions \> OH^- ions*

Question 28

* Explain why 1,6-diaminohexane and hexanedioic acid can undergo polymerisation * Which type of polymerisation would occur? * Draw the repeating unit for this polymer * What type of polymer is this?

Answer 28

* Both molecules have reactive groups in 2 places (amine and carboxyl) * Condensation polymerisation * A polyamide (nylon)

Question 29

How are nylons named?

Answer 29

* According to the number of carbons in monomers * If one monomer with 6 Cs was used, it would be nylon-6 * If two monomers, with 5 and 6 Cs, were used, it would be nylon-5,6

Question 30

* Write an equation to show the polymerisation of 1,6-diaminohexane and decanedioyl chloride * Name the polymer formed

Answer 30

Question 31

* Name this polymer * Explain how it was formed --(NH(CH₂)₅CO)--_n

Answer 31

* Nylon-6 * Made from a single monomer containing both an amine and COOH / COCl group: nH₂N(CH₂)₅COOH / nH₂N(CH₂)₅COCl

Question 32

Name the mechanism that occurs during: * Condensation polymerisation * Addition polymerisation

Answer 32

* Nucleophilic substitution * Electrophilic addition

Question 33

Draw the repeating unit of the polymer that can be obtained from 3-aminobenzoic acid.

Answer 33

Question 34

Draw a mechanism representing the formation of polypropene.

Answer 34