3.11 - Amines

Question 1

How do you name amines?

Answer 1

-amine
amino-

Question 2

Why are amines so reactive?

Answer 2

The lone pair of electrons on the Nitrogen - due to polar N-H bond

Question 3

What shape are amines around the N? Bond angle?

Answer 3

Trigonal pyramidal, 107 degrees due to lne pair on N

Question 5

What kinds of intermolecular forces do they have and why?

Answer 5

Hydrogen bonding due to polar N-H bond and lone pair of electrons on N atom

Question 6

Do amines have intermolecular forces which are stronger than or weaker than alcohols? Why?

Answer 6

Weaker, as N has a lower electronegativity than O –> weaker hydrogen bonding.

Question 7

What state are amines at 298K?

Answer 7

Short chains are gases, longer chains are volatile liquids.

Question 8

What do they smell of? Why?

Answer 8

Fishy smell - rotting fish/flesh releases di- and triamines.

Question 9

Which primary amines are soluble in water/ alcohols? Why?

Answer 9

Up to 4 carbon atoms, as they can hydrogen bond to water molecules. After this, non-polarity of hydrocarbon chain makes them insoluble.

Question 10

What kind of solvents are most other amines soluble in?

Answer 10

Less or non-polar solvents

Question 11

Solubility of phenylamine? Why?

Answer 11

Not very soluble due to the non-polarity of the nenzene ring - C6H5 cannot form hydrogen bonds.

Question 12

How can/ when do amines act as bases?

Answer 12

When they bond with a H+ ion

Question 13

How can/ when do amines act as nucleophilles?

Answer 13

When they bond with an electron-deficient C atom - donate a lone pair from N

Question 14

What is the product from the basic action of an amine with water?

Answer 14

RNH3+ - ammonium ion, which forms a salt with an anion.

Question 15

Is an ammonium ion soluble in salt? Why?

Answer 15

Yes as it is ionic so is attracted to the polar bonds in H20.

Question 16

How could you regenerate the soluble amine from the ammonium salt?

Answer 16

Add a strong base (NaOH) -> removes H+ ions drom ammonium ion.

Question 17

In order to be the strongest base, what must a particular amine have out of a set of amines?

Answer 17

Greatest electron density around the N atom, making it a better electron pair donor

Question 19

What does positive/negative inductive effect mean?

Answer 19

Positive inductive effect = donate electrons, increase density around N
Negative means remove eletrons, decrease density around N

Question 20

What effect do alkyl groups have on electron density and base strength?

Answer 20

Positive inductive effect - increase electron density aroun N –> stronger base

Question 21

What effect do aryl groups have on electron density and base strength?

Answer 21

Negative inductive effect - decrease electron density around N –> weaker base

Question 22

Why are 3° amines never good bases?

Answer 22

They are insoluble in water

Question 23

Place these in order of base strength ( weakest to strongest):
- NH3
- 1° amine
- 2° amine
- Phenylamine

Answer 23

2° amine
1° amine
NH3
phenylamine

Question 24

How can primary amines then from 2°, 3° amines and 4° ammonium ions?

Answer 24

Multiple substitutions; primary amine is a nucleophile that attacks the original haloalkane etc

Question 25

What are the problems with this method?

Answer 25

Not efficient as low yield of 1° amine due to multiple substitutions

Question 26

How would you maximise the yield of the primary amine?

Answer 26

Use excess ammonia

Question 27

What type of mechanism is the reaction of a haloalkane with a cyanide ion?

Answer 27

Nucleophilic substitution

Question 28

What conditons does this reaction require? What is the product formed?

Answer 28

Ethanol as a solvent A nitrile is formed

Question 29

How do you get from a nitrile to a primary amine?

Answer 29

Reduction using either Nickel or Hydrogen catalyst

Question 30

Why is this a purer method of a synthesising amines?

Answer 30

Only the pimary amine can be formed

Question 31

What conditions are needed to form nitrobenzene from benzene?

Answer 31

Concentrated H2SO4 and HNO3 to form the NO2+ ion for electrophilic attack.

Question 32

How do you form an ammonium chloride salt from nitrobenzene? What conditions are needed?

Answer 32

Reduce the nitrile using Tin / HCl --> forms an ammonium salt with CL- ions Room temperature

Question 33

Equation for the reaction of nitrobenzene to phenylamine

Answer 33

C6H5NO2 + 6[H] --> C6H5NH2 + 2H20

Question 34

What mechanism is used to form amides from acyl chlorides and amines?

Answer 34

Nucleophilic addition / elimination

Question 35

In which industries / products are amines used?

Answer 35

Dyes, nylon, drugs, synthesis of new molecules

Question 36

What are cationic surfactants used in fabric/ hairconditioners)?

Answer 36

Quaternary ammonium salts, with a cation that is charged at one end (N+) and non-polar at the other.

Question 37

How do cationic surfactants work in fabric/hair conditioners?

Answer 37

Negative charges on the surface of the fabric/hair are attracted to the cation, removing them from the surface; prevents build-up of static electricity and keeps hair flat and fabric smooth.

Question 38

How do cationic surfacants sit when placed in water?

Answer 38

Charged end in the water, non-polar end sticking out of the water/ at the surface.