AS Organic Chem

Question 1

Define stereoisomers

Answer 1

• same molecular formula and structural formula
• but differ in the arrangement of bonds in space

Question 2

What must be present in a molecule if it is to exhibit cis-trans or E-Z isomerism?

Answer 2

• restricted rotation around a C=C double bond due to the formation of the pi bond
• 2 different atoms/groups on the carbon atoms at both ends of the double bond
• ** ring** structures will also exhibit **geometric ** isomerism due to restricted rotation in the ring

Question 3

What is a cis isomer

Answer 3

• same group or atoms are on the same side of the C=C

Question 4

What is a trans isomer?

Answer 4

• same group or atoms are on the opposite side of the C=C

Question 5

What is a (1) Z isomer (2) E isomer

Answer 5

(1) higher priority atom is on the same side of the C=C
(2) higher priority atom is on the opposite side of the C=C

Question 6

How do we dispose the plastics

Answer 6

• bury them in landfill sites
• incinerating the plastics
• recycling

Question 7

What is the problem with burying polyalkene plastics in the landfill sites?

Answer 7

• they are non-biodegradable
• so burying them means that landfill sites quickly fill up

Question 8

Methane gas is released from landfill, so what is the problem with that?

Answer 8

• methane is a greenhouse gas
• so contributes to global warming

Question 9

What is an advantage and disadvantage of incinerating plastics

Answer 9

• generates electricity
• increases the amount of greenhouse gases (CO2)

Question 10

Electrophile

Answer 10

• electron pair acceptor
• attracted to a region of high electron density

Question 11

Stability of tertiary > secondary > primary
Why?

Answer 11

• Alkyl groups (e.g. CH3) have a positive inductive effect, which means they are electron releasing = “push” the bond pair electrons towards the carbocation

Question 12

Define electronegativity

Answer 12

• Power/ ability of an atom to attract the bond pair of electrons towards itself in a covalent bond

Question 13

What is hydrogenation?

Answer 13

• addition of hydrogen (H2) by breaking C=C double bond(s)

Question 14

C3H7CH=CH2 + H2 -> CH3CH2CH2CH2CH3
Must show where the reaction took place

What are the
- Change in function group
- Reagent
- Conditions
- Type of reaction

Answer 14

• Change in function group: Alkene -> alkane
• Reagent: hydrogen
• Conditions: Nickel catalyst (Ni, also heat!)
• Type of reaction: Addition

Question 15

Which bond is weaker, π bond or σ bond?

Answer 15

π bond
- areas with high electron density
- more accessible to electrophilic attack by electrophile

Question 16

Reaction of alkenes with bromine/chlorine

Answer 16

• Change in functional group: alkene -> dihalogenoalkane
• Reagent: Bromine (dissolved in organic solvent- orange/brown)
• Conditions: Room temp
• Mechanism: Electrophilic addition
• Type of Bond fission: heterolytic

Question 17

Reaction of hydrogen bromide with alkenes

Answer 17

• Change in functional group: alkene -> halogenoalkane
• Reagent: HCl or HBr
• Conditions: room temp
• Mechanism: electrophilic addition

Question 18

Reaction of bromine water (BrOH) with alkenes (test for double bond)

Answer 18

• Reagent: bromine dissolved in water (aq)
• Conditions: room temp
• Type pf reaction: addition
• Observation: orange/brown -> colourless (decolourize)

Question 19

Reaction of potassium manganate(VII) with alkenes

Answer 19

alkene + [O] + H2O -> diol
- Change in functional group: alkene -> diol
- Reagent: KMnO4 in an acidified solution
- Conditions: room temp
- Type of reaction: oxidation
- Observation: purple to colourless

Question 20

Reaction of steam with alkenes

Answer 20

• Change in functional group: alkene -> alcohol
• Reagent: H2O (g)
• Condition: H3PO4 (catalyst)
  High atom economy (100%)