module 6 ppqs

Question 1

26) describe what is happening to the electron pairs and bonds in step 1 of the nucleophilic addition mechanism [3]

Answer 1

1. electron pair on H- is attracted to δ+ carbon forming a dative covalent bond
2. double electron pair breaks
3. electron pair now on O-

Question 2

26) outline how to distinguish between an aldehyde and a ketone after 2,4-DNP [3]

Answer 2

1. recrystallise to purify the precipitate
2. measure melting point
3. compare with known values

Question 3

describe how to purify impure crystals [3]

Answer 3

1. dissolve in minimum quantitity of hot solvent
2. cool to allow crystals to form and then filter under reduced pressure
3. leave to dry

Question 4

explain why phenols are more easily nitrated than benzoic acids [3]

Answer 4

1. phenol has a lone pair of electrons on the oxygen which is partially delocalised into the pi-ring
2. benzoic acid has a -COOH group which is an electron withdrawing group
3. in phenol, electron density is higher so the ring is more susceptible to attack