Key Stuff - Module 4 + 6

Question 1

Homologous Series

Answer 1

Series of organic compounds having the same functional group but with each successive member differing by CH2

Question 2

Structural isomers

Answer 2

Compounds with the same molecular formula but different structural formulae

Question 3

Radical

Answer 3

A species with an unpaired electron

Question 4

Describe the trends in boiling points of alkanes

Answer 4

• ↑in chain length = ↑ points contact = ↑ induced d-d interaction - ↑ BP
• Branched molecules have ↓ points contact = ↓ induced d-d interaction - ↓ BP

Question 5

Why do alkanes have relatively low reactivity?

Answer 5

• ↓ bond polarity of sigma bond
• ↑ bond enthalpy

Question 6

Steroisomers

Answer 6

Compounds with same structural formula but with different arrangement in space

Question 7

E/Z isomerism

Answer 7

• Causes by restricted rotation about the double bond
• requires X2 diff groups to be attached to each C atom of C=C

Question 8

Cis/Trans Isomerism

Answer 8

• Special type of E/Z isomerism
• Where 2 of substituent groups attached to each C atom of C=C group are the same

Question 9

Electrophile

Answer 9

Electron pair acceptor

Question 10

Nucleophile

Answer 10

Electron pair donor

Question 11

Outline mechanism for production of halogen radicals + breaking down of ozone layer

Answer 11

Question 12

Evidance against Kekule’s benzene model

Answer 12

• C-C bonds all same length - C=C should be shorter
• It doesn’t undergo addition reactions easily
• ΔH hydrogenation about 152 kJ mol-1
  less than expected

Question 13

For electrophillic mechanism which way does the curly arrow go?

Answer 13

From double bond to the species

Question 14

For nucleophillic mechanisms which way does the curly arrow go?

Answer 14

From the species to the compound

Question 15

Why is benzene less reactive then its alkene?

Answer 15

• Benzene’s π electrons are delocalised whereas alkenes π electrons are localised bt/w 2 C’s - electron density lower in benzene
• The lower electron density means that electrophiles are less attracted
• Therefore less reactive

Question 16

Why is phenol more reactive then benzene?

Answer 16

• As the lone pair of e- on the O
• Partially delocalised into the π ring
• Making phenol more susceptible to electrophilic attack

Question 17

How do you name & draw an ester?

Answer 17

• ‘thyl’ - from alcohol
• ‘oate’ from acid/anhydride
• alchol on the right (attached to single bonded O)

Question 18

Describe Zwitterion

Answer 18

• At specific pH - isoelectric pH + in crystalline solid - amino acid will exist as zwitterion
• Protons transferred internally from COOH to NH2

Question 19

Optical isomerism

Answer 19

Non-superimposable mirror image about a chial centre

Question 20

Outline the marking points of how you obtain a pure sample of something from impure solid

Answer 20

Recrystallisation:
1. dissolve in min vol of hot solvent
2. Cool solution + filter solid under reduced pressure
3. Wash with cold solvent + let dry

Check Purity:
1. Obtain melting point via melting point appratus
2. Compare to known values - closer to value the purer the sample

Question 21

Outline the marking points of how seperate insoluble liquid from water

Answer 21

1. Add to seperating funnel, shake + let settle
2. Run off the water layer
3. Collect organic layer in seperate beaker
4. Add anhydrous magnesium sulphate/calcium chloride
5. Redistil organic layer + collect fraction bt/w BPs given

Question 22

Define

Question 23

Give X2 similarities + X1 difference bt/w delocalised model for benzene + Kekule model

Answer 23

Similarities:
- Overlap of p orbitals
- Pi system above + below the plane

Difference:
- Kekule has alternating pi bonds whereas delocalised as overlap of all p obitals