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This question is about isomers with the molecular formula C₄H₈O - AQA - A-Level Chemistry - Question 6 - 2021 - Paper 2
Question 6
This question is about isomers with the molecular formula C₄H₈O. 6.1 Draw the skeletal formula of a branched chain aldehyde with molecular formula C₄H₈O that is opt... show full transcript
Worked Solution & Example Answer:This question is about isomers with the molecular formula C₄H₈O - AQA - A-Level Chemistry - Question 6 - 2021 - Paper 2
Step 1
6.1 Draw the skeletal formula of a branched chain aldehyde with molecular formula C₄H₈O that is optically active.
Answer
The skeletal formula of a branched chain aldehyde (butanal) could be represented as follows:
CH₃
|
CH₃-C-CHO
|
H
The presence of the chiral center on the second carbon makes it optically active.
Step 2
6.2 Describe how you distinguish between separate samples of the two enantiomers of the branched chain aldehyde C₄H₈O.
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).
Step 3
6.3 Draw the E and Z forms of a structural isomer of C₄H₈O that shows both optical and geometric isomerism.
Answer
The E and Z forms of a suitable structural isomer could be:
E isomer
OH
|
CH₃-C=CH-CHO
|
H
Z isomer
OH
|
C=CH-CHO
CH₃ |
H
Both forms demonstrate geometric isomerism due to the presence of a double bond and optical isomerism due to the chiral center.
Step 4
6.4 Draw two other cyclic isomers of C₄H₈O that have an ether functional group and only three peaks in their ¹³C NMR spectra.
Answer
Two cyclic isomers of C₄H₈O with ether functional groups include:
Isomer 1
CH₂
/ \
-O- CH
| |
CH---CH₂
Isomer 2
CH
/
O
|
CH₂---CH₂
| \
CH H
Both isomers can be expected to show only three peaks in their ¹³C NMR spectra due to symmetry.