Photo AI
9. The alkenes are a homologous series - Leaving Cert Chemistry - Question 9 - 2006
Question 9
9. The alkenes are a homologous series. Ethene (C2H4) is the first member of the series. (a) What is meant by a homologous series? (b) Ethene may be made in a sch... show full transcript
Worked Solution & Example Answer:9. The alkenes are a homologous series - Leaving Cert Chemistry - Question 9 - 2006
Step 1
What is meant by a homologous series?
Answer
A homologous series is a group of organic compounds that share the same functional group and exhibit a gradual change in physical properties. The general formula for alkenes is CnH2n, indicating that each successive compound differs by a −CH2− group.
Step 2
Step 3
Step 4
What precaution should be observed when heating is stopped? Why is this necessary?
Answer
When heating is stopped, the delivery tube should be removed from the water trough to prevent back-suction. This prevents any liquid from being sucked back into the apparatus, which could lead to contamination or damage.
Step 5
Step 6
Describe the mechanism for the bromination of ethene.
Answer
The mechanism for the bromination of ethene involves the electrophilic addition of bromine (Br2) across the double bond of ethene. The formation of a cyclic bromonium ion intermediate occurs when Br2 approaches the double bond, leading to the generation of a positively charged species. This species is then attacked by a Br− ion, resulting in the formation of 1,2-dibromoethane.
Step 7
State and explain one piece of experimental evidence to support this mechanism.
Answer
One piece of experimental evidence is the observation that the reaction proceeds via an anti-addition mechanism. When ethene reacts with Br2 in the presence of a solvent such as dichloromethane, the product shows a specific stereochemical configuration, indicating that the bromination occurs from opposite sides of the double bond.
Step 8