Study the reaction scheme and answer the questions which follow - Leaving Cert Chemistry - Question 6 - 2003
Question 6
Study the reaction scheme and answer the questions which follow.
(a) Which of the compounds A, B and C has no tetrahedrally bonded carbon atoms?
Draw the structur... show full transcript
Worked Solution & Example Answer:Study the reaction scheme and answer the questions which follow - Leaving Cert Chemistry - Question 6 - 2003
Step 1
Which of the compounds A, B and C has no tetrahedrally bonded carbon atoms? Draw the structure of a molecule of this compound.
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Answer
Compound C has no tetrahedrally bonded carbon atoms. It is a molecule of ethylene, which contains a double bond between the two carbon atoms. The structure of ethylene (C2H4) can be drawn as follows:
H H
\ /
C=C
/ \
H H
Step 2
Classify the conversions X, Y and Z as addition, substitution or elimination reactions.
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Answer
Conversion X: Addition reaction.
Conversion Y: Addition reaction.
Conversion Z: Substitution reaction.
Step 3
What reagent is used to convert A to C?
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Answer
The reagent used to convert A (C2H4) to C is hydrogen chloride (HCl).
Step 4
What reagent and what conditions are required for the conversion of B to C?
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Answer
The reagent needed for the conversion of B to C is chlorine (Cl2) or dichloroethane (C2H2Cl2) and the condition required is ultraviolet (UV) light.
Step 5
Describe the mechanism of the reaction for the conversion of A to C.
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Answer
The mechanism involves the following steps:
The double bond in ethylene (A) approaches the hydrogen of the HCl molecule, leading to the cleavage of the H-Cl bond.
The electrons from the double bond move to form a bond with the hydrogen atom, creating a positively charged carbon ion.
The chloride ion (Cl-) attacks the positively charged carbon, completing the substitution reaction where A is converted to C.
Step 6
State one piece of experimental evidence which supports the mechanism you have proposed.
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Answer
One piece of evidence is the addition of bromine water, which shows that ethylene can react to form 2-bromoethanol, indicating that the double bond is involved in the reaction process.
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