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This question is about isomers with the molecular formula C₅H₈O - AQA - A-Level Chemistry - Question 6 - 2021 - Paper 2
Question 6
This question is about isomers with the molecular formula C₅H₈O. 1. Draw the skeletal formula of a branched chain aldehyde with molecular formula C₅H₈O that is opti... show full transcript
Worked Solution & Example Answer:This question is about isomers with the molecular formula C₅H₈O - AQA - A-Level Chemistry - Question 6 - 2021 - Paper 2
Step 1
1. Draw the skeletal formula of a branched chain aldehyde with molecular formula C₅H₈O that is optically active.
Answer
The skeletal formula can be represented as:
CH₃
|
CH₃-CH-CHO
|
CH₂
This structure indicates a branched aldehyde that is optically active due to the presence of a chiral center.
Step 2
2. Describe how you distinguish between separate samples of the two enantiomers of the branched chain aldehyde C₅H₈O.
Answer
To distinguish between the two enantiomers, you can use plane-polarized light. One enantiomer will rotate the plane of polarized light in one direction (clockwise), while the other will rotate it in the opposite direction (counterclockwise). This property is known as optical activity.
Step 3
3. Draw the E and Z forms of a structural isomer of C₅H₈O that shows both optical and geometric isomerism.
Answer
The E and Z forms can be represented as follows:
E isomer:
CH₃
|
CH₃-CH-CHO
|
CH₂
Z isomer:
CH₃
|
CH₃-CH=CHO
|
CH₂
In this case, the E isomer has higher priority groups (based on Cahn-Ingold-Prelog rules) on opposite sides of the double bond, while the Z isomer has them on the same side.
Step 4
4. Draw two other cyclic isomers of C₅H₈O that have an ether functional group and only three peaks in their ¹³C NMR spectra.
Answer
The cyclic isomers can be represented as follows:
Isomer 1:
O
/ \
C C
| |
C-----C
Isomer 2:
O
/ \
C C
| |
C-----C
Both isomers have ether groups and would show three distinct peaks in their ¹³C NMR spectra due to symmetry.