Amines

Question 1

How do you name amines?

Answer 1

-amine or 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, 107o due to lone pair on N

Question 4

What kind of intermolecular forces do they have? Why?

Answer 4

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

Question 5

What state are amines at 298K?

Answer 5

Short chains are gases, longer chains are volatile liquids

Question 6

What do amines smell of? Why?

Answer 6

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

Question 7

Which primary amines are soluble in water/alcohols?

Why?

Answer 7

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

Question 8

What kind of solvents are most other amines soluble

in?

Answer 8

Less or non-polar solvents

Question 9

Solubility of phenylamine? Why?

Answer 9

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

Question 10

How can/when do amines act as bases?

Answer 10

When they bond with a H+ ion

Question 11

How can/when do amines act as nucleophiles?

Answer 11

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

Question 12

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

Answer 12

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

Question 13

Is the product (ammonium ion) soluble in water? Why?

Answer 13

Yes, as it is ionic so is attracted to the polar bonds in H2O

Question 14

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

Answer 14

Add a strong base (NaOH) → removes H+ ions from ammonium ion

Question 15

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

Answer 15

Greatest electron density around the N atom, making it a better electron pair donor (attracts protons more)

Question 16

What does positive/negative inductive effect mean?

Answer 16

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

Question 17

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

Answer 17

Positive inductive effect - increase electron density around N → stronger base

Question 18

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

Answer 18

Negative inductive effect - decrease electron density around N → weaker base

Question 19

Why are 3o amines never good bases?

Answer 19

They are insoluble in water

Question 20

Place these in order of base strength (in general):

NH3, 1o amine, 2o amine, phenylamine

Answer 20

2o amine > 1o amine > NH3 > phenylamine

Question 21

How can primary amines then form 2o, 3o amines and 4o ammonium ions?

Answer 21

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

Question 22

What are the problems with this method?

Answer 22

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

Question 23

How would you maximise the yield of the primary amine?

Answer 23

Use excess ammonia

Question 24

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

Answer 24

Nucleophilic substitution

Question 25

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

Answer 25

Ethanol as a solvent

A nitrile is formed

Question 26

How do you get from a nitrile to a primary amine? (name of reaction type and reagents/catalysts)

Answer 26

Reduction using Nickel / Hydrogen catalyst

Question 27

Why is this the reduction a purer method of synthesising amines?

Answer 27

Only the primary amine can be formed

Question 28

What conditions are needed to form nitrobenzene from benzene?

Answer 28

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

Question 29

How do you form an ammonium chloride salt from

nitrobenzene? What conditions are needed?

Answer 29

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

Question 30

Equation for the reaction of nitrobenzene → phenylamine?

Answer 30

C6H5NO2 + 6[H] → C6H5NH2 + 2H2O

Question 31

What mechanism is used for forming amides from acyl chlorides and amines?

Answer 31

Nucleophilic addition/ elimination

Question 32

In which industries/products are amines used?

Answer 32

Dyes, nylon, drugs, synthesis of new molecules

Question 33

What are cationic surfactants (used in fabric/hair conditioners)?

Answer 33

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

Question 34

How do cationic surfactants work in fabric/hair conditioners?

Answer 34

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 35

How do cationic surfactants sit when placed in water?

Answer 35

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