Alkenes

Question 1

How do cis-trans isomers arise in alkenes?

Answer 1

• restricted rotation due to the pi bond.
• there are 2 different groups bonded to each C atom

Question 2

Why can’t ring alkenes has cis-trans isomerism?

Answer 2

• high ring strain may cause it to break

Question 3

Properties of cis-trans isomers

Answer 3

Cis-trans isomers have similar chem properties, diff physical properties.
.
- Cis: higher bp ad solubility in water due to pd-pd, while trans only has id-id
.
- Cis: More polar than trans
.
- Cis: lower mp than trans due to lower symmetry, poorer packing by of molecules
.
- Cis less stable than trans bcuz bulkier species are closer tgt, greater steric hindrance

Question 4

All alkenes rxn, reagents and conditions

Answer 4

1. C=C + H2 —> CH3CH3
   Type: Reduction
   R: H2(g), Ni catalyst
   C: Heat
   .
2. C=C + X2 (in CCl4) —> CH2XCH2X
   R: X2 in CCl4
   C: No UV, rtp
   .
3. C=C + X2(aq) —> CH2XCH2(OH)
   R: X2
   C: No UV, rtp
   .
4. C=C + HX(g) —> CH2XCH3
   R: Dry HX gas
   C: heat ⁉️⁉️
   .
5. C=C + H2O —> CH3CH2(OH)
   R: steam, H3PO4 catalyst
   C: Heat