organic standard answers

Question 1

Explain the term carbonyl compound

Answer 1

a compound containing and aldehyde or ketone functional group

Question 2

Describe a test to show that a compound contains either aldehyde or ketone functional group

Answer 2

Brady’s reagent
deep orange precipitate formed

Question 3

Explain how the crystals from the brady’s reaction can be used to confirm the identity of a specific carbinyl compound

Answer 3

filter ppt
recrystallise and allow crystals to dry
measure the melting point and compare this to a database

Question 4

Describe the evidence for the delocalized model of benzene

Answer 4

benzene doesnt react with bromine (no electrophilic reactions)
enthalpy change is less exothermic so it must be more stable
all bonds have the same length in x-ray diffraction

Question 5

Describe the bonding in the delocalized model of benzene

Answer 5

one delocalized pi bond
6 electrons between 6 carbons
formed by sideways overlap of p orbitals
above and below the ring

Question 6

Bonding in the kekule model of benzene

Answer 6

three localized pi bonds
each contain 2 electrons between 2 carbon atoms
formed by the sideways overlap of p orbitals
above and below the ring

Question 7

Describe the similarities between the kekule and delocalized model

Answer 7

pi bond formed by the sideways overlap of p orbitals
above and below the ring

Question 8

Describe the differences between the kekule and delocalised model of benzene

Answer 8

p orbitals overlap in one direction
3 alternating pi bonds
each pi bond contains two electrons
higher electron density than delocalised
p orbitals overlap in both directions
one pi ring
the pi bond contains six delocalised electrons
lower electron density then delocalised

Question 9

Describe the relative resistance to bromination of benzene compared to cyclohexane

Answer 9

benzene doesnt react with bromine
benzene has a delocalised pi bond
cyclo reacts with bromine
cycle localised pi bond with greater electron density
cyclo id better able to attract an electrophile

Question 10

Explain why phenol is more reactive then benzene

Answer 10

the lone pair of electrons from oxygen delocalise into the ring
increases the electron density in the ring so more susceptible to electrophilic attack

Question 11

Explain why the reaction of phenylamine with dilute nitric acid produces a mixture of products

Answer 11

-NH2 is electron releasing
directs substitution to positions 2 and 4

Question 12

Explain why the reaction of nitrobenzene with Cl produces mainly one product

Answer 12

-NO2 is electron withdrawing
directs substitution to positions 3 and 5