TAMRALIPTA MAHAVIDYALAYA
On-line Test - 2019-20
Subject: Organic Chemistry (C10T)
Semester: IV
Exam Date: 26-04-2020
Full Marks: 30
Time: 2 hr.
Answer all questions.
1. Define the terms “donor synthon” and “acceptor synthon” with suitable example.
Write their corresponding synthetic equivalents.
3
2. Propose all possible disconnection/retro-synthesis for the following 1,4-dicarbonyl
molecule. Consider the pattern of functional groups when determining the best site for
a disconnection. Write forward syntheses also.
8
3. The following reaction gives a different product from what we expect. What is the
actual product? Why is that product formed? Suggest a suitable synthetic route that
will give the desired product as shown below.
4
4. Propose a possible retro-synthesis for the following target molecules. Show forward
synthesis also (any three).
6
5. Starting with 2-methylcyclohexanone, provide a synthesis of the following target
molecules. It may help to first do a retro-synthesis of the TM.
3
6. Provide necessary reagents/products for each of the steps of the following multistep
synthesis.
6
SEM-IV C10T
Synthesis
April-2020
TAMRALIPTA MAHAVIDYALAYA
On-line Test - 2019-20
Subject: Organic Chemistry (C10T)
Semester: IV
Exam Date: 26-04-2020
Full Marks: 30
Time: 2 hr.
Answer paper
1. Define the terms “donor synthon” and “acceptor synthon” with suitable example. Write their
corresponding synthetic equivalents.
3
Answer: Based on electronic nature (anionic or cationic), synthons can be classified as donor
synthons and acceptor synthons. If a synthon is anionic in nature, i.e., nucleophilic and donates
electron pair to form bond, then the synthon is known as donor synthon. Idealized anionic fragments
resulting from disconnection of a -bond in the target molecule during retrosynthetic analysis are
called donor synthons. For example,
If a synthon is cationic in nature, i.e., electrophilic and accepts electron pair to form bond, then the
synthon is known as acceptor synthon. Idealized cationic fragments resulting from disconnection of
a -bond in the target molecule during retrosynthetic analysis are called acceptor synthons. For
example,
OR
SEM-IV C10T
Synthesis
April-2020
2. Propose all possible disconnection/retro-synthesis for the following 1,4-dicarbonyl molecule.
Consider the pattern of functional groups when determining the best site for a disconnection. Write
forward syntheses also.
8
Answer:
Write forward synthesis accordingly.
3. The following reaction gives a different product from what we expect. What is the actual product?
Why is that product formed? Suggest a suitable synthetic route that will give the desired product as
shown below.
4
Answer:
The carbanion of cyclopentenone is in equilibrium with its conjugate acid, cylcopentanone. Since
cyclopentanone is more reactive than vinyl acetone towards nucleophilic reagent, the selfcondensation (Aldol Condensation) product is formed as the actual product rather than Michael
addition product.
SEM-IV C10T
Synthesis
April-2020
To get the desired product, use either pre-formed enolate or introduce activating group at position of cyclopentenone.
4. Propose a possible retro-synthesis for the following target molecules. Show forward synthesis also
(any three).
6
Answer:
i) Retro-synthesis:
SEM-IV C10T
Synthesis
April-2020
Synthesis:
ii) Retro-synthesis:
Synthesis:
iii) Retro-synthesis:
SEM-IV C10T
Synthesis
April-2020
Synthesis:
iv) Retro-synthesis:
Synthesis:
5. Starting with 2-methylcyclohexanone, provide a synthesis of the following target molecules. It
may help to first do a retro-synthesis of the TM.
3
Answer:
Retro-synthesis:
SEM-IV C10T
Synthesis
April-2020
Synthesis:
6. Provide necessary reagents/products for each of the steps of the following multistep synthesis.
6
Answer:
ii)
END
SEM-IV C10T
Synthesis
April-2020