2 Flashcards
Stereoisomer
- Same structual formula
- different spatial arrangement
- Determine a method to obtain pure sample of
3-nitrobenzoic acid from the impure solid - Check its purity
Purification:
1. Recrystallisation
2. Dissolve impure solid in minimum volume of hot water/solvent
3. Cool solution and filter solid
4. Wash with cold water/solvent and dry
Checking purity:
1. Obtain melting point
2. Compare to known values
3. Pure sample will have a (sharp) melting point very close to data book value
Why is it easier to nitrate phenol than benzoic acid
Phenol:
* a (lone) pair of electrons on O2 is (partially) delocalised/donated into the benzene ring
Benzoic acid:
- COOH group is e- withdrawing group
Comparison:
- e- density higher in phenol
AND
The ring is more susceptible to attack
Why is a polymer biodegradable
ester group can be hydrolysed
State and explain how the halogen in the haloalkane affects the rate of hydrolysis
- Links rate of reaction to strength of bond/bond enthalpy
i.e. the weaker the bond the faster the reaction - Correct comparison of rate of reaction for at least two C– Hal bonds
i.e. C–F bond is hydrolysed slowest
C–I bond is hydrolysed faster than C–Br
C–Br has shorter reaction time than C–Cl
Explain boiling points of straight chain and branched molecules
- Longer hydrocarbon chain = more points of contact between molecules
- Longer hydrocarbon chain = more e- so stronger London forces
- Branching reduces surface contact between molecules
Describe, in terms of orbital overlap, the similarities and differences between the bonding in the Kekulé model and the delocalised model of benzene.
Similarity:
Sideways overlap of P orbitals
π bond:
π bond above and below bonding C atoms
Difference:
Kekule has alternating π bonds
AND
Delocalised has π ring system
Describe two pieces of evidence to support the delocalised model of benzene
- all (C–C) bond lengths are the same
- ∆H hydrogenation less exothermic than expected
- Benzene is less reactive than alkenes
