Alkenes

Question 1

Why is there no rotation around a C=C bond?

Answer 1

• The Pi bond is formed by overlap of P orbitals
• if there was any rotation, the P orbitals would no longer overlap + the Pi bond would break

Question 2

For electrophilic addition by H-Br, what is the:

• Reagent
• Type of product

Answer 2

• HCl, HBr <—- Hydrogen Halide
• Haloalkane

Question 3

Electrophilic addition with Ethene to bromoethane?

Answer 3

https://www.savemyexams.com/a-level/chemistry/ocr/17/revision-notes/4-core-organic-chemistry/4-3-alkenes/4-3-4-electrophilic-addition/

Question 4

Explain why 2-bromopropane is the major product compared to 1-bromopropane?

Answer 4

• 2-bromopropane is made from a secondary carbocation
• 1-bromopropane is made from a primary carbocation
• Secondary carbocations are more stable than primary due to the positive inductive effect of the 2 alkyl groups

Question 5

For electrophilic addition by Br2, what is the:

• Reagent
• Type of product

Answer 5

• Cl2, Br2 (Halogen)
• Haloalkane (Dihaloalkane)

Question 6

Electrophilic addition with Ethene through Br2?

Answer 6

https://www.savemyexams.com/a-level/chemistry/edexcel/17/revision-notes/3-organic-chemistry/3-3-alkenes/3-3-4-electrophilic-addition-mechanism/

Question 7

Explain why bromine molecules react with the double bonds in alkenes?

Answer 7

• C=C bond is electron rich and induces a dipole in the Br2
• Partially +ve Br is attracted to the C=C bond

Question 8

• Reagent used to test for alkenes
• Observation when alkenes present
• Observation when alkene not present

Answer 8

• Br2
• Orange to colourless
• No visible change

Question 9

Structural formula for H2SO4 for electrophilic addition?

Answer 9

H—OSO2OH

Question 10

For electrophilic addition by sulphuric acid, what is the:

• Reagent
• Type of product

Answer 10

• H2SO4
• Alkyl hydrogen sulfate

Question 11

Electrophilic addition with ethene through sulphuric acid?

Answer 11

https://shout.education/ChemKey/mechanisms/eladd/symh2so4.html

Question 12

For electrophilic addition by direct hydration, what is the:

• Reagent
• Conditions
• Type of product

Answer 12

• H2O
• Concentrated H3PO4 catalyst
• Alcohol

Question 13

Electrophilic addition with ethene through direct hydration?

Answer 13

https://studymind.co.uk/notes/industrial-production-of-alcohols/

Question 14

Write equation for the formation of an addition polymer from ethene?

Answer 14

https://www.chemistrystudent.com/additionpolymerisation.html

Question 15

Explain the difference between structural isomerism and stereoisomerism. Use examples to show how compounds with molecular formula C4H8 exhibit stereoisomerism and 3 types of structural isomerism?

Answer 15

Structural isomers - Molecules with same molecular formula but different structure
Stereoisomers - Molecules with same structural formula but different arrangement of atoms in space

Stereoisomers
2a lack of rotation around C=C
2b structures of E- and Z-but-2-ene
2c correct identity of E and Z isomers

Structural isomers
3a different C chain, e.g. methylpropene & but-1-ene / but-2-ene
3b different position of functional group e.g. but-1-ene & but-2-ene
3c different functional group, e.g. cyclobutane & but-1-ene / but-2-ene / methylpropene

Question 16

Explain why poly(propene) is unreactive?

Answer 16

No polar bonds