BPSC PGT Chemistry Important Question: Structural Representations of Organic Compounds

1. Identify the condensed formula of the given compound from the following.
ClCH₂CH₂CH₂CH₂CHCH₂CH₂CH₂CHCH₂CH₃
a) Cl (CH₂)₂ (CH₂)₂CH (CH₂)₂CH₂CH₂CH₃
b) Cl (CH₂)₃CH₂CHCH₂CH₂CH₂CH (CH₃) ₂
c) Cl (CH₂)₄CH (CH₂)₃CH (CH₂) CH₃
d) Cl (CH₂)₃CH₂CH₂CH (CH₃)₂CH₃CHCH₂CH₃

Answer: c
Explanation: To write the condensed formula, group together all the repeating CH₂ units and ensure that each carbon forms exactly four bonds. In the given structure ClCH₂CH₂CH₂CH₂CHCH₂CH₂CH₂CHCH₂CH₃, there are four consecutive CH₂ groups, which can be written as (CH₂)₄. Applying the same method to the rest of the chain and combining the CH₂ units accordingly, we arrive at the condensed formula of the molecule.

2. Identify the condensed formula of ethane from the following.
a) CH₃-CH₃
b) HC-H₂-C-H₃
c) CH₂=CH₂
d) CH₃-CH₂

Answer: a
Explanation: In a condensed formula, all atoms are written out, but single bonds are usually not shown. However, double and triple bonds are represented. The formula CH₂=CH₂ does not represent ethane; it represents ethene.

3. Determine the bond-line formula of CH₃CH₂COCH₂CH₃.
a)
b)
c)
d)

Answer: c
Explanation: In the compound CH₃CH₂COCH₂CH₃, the ketone group (C=O) is bonded to the third carbon atom. Therefore, the double bond must be shown at the position of the third carbon, that is, at the end of the second line. In all the other options, the ketone group is not located on the third carbon, which makes them incorrect.

4. Which is not a heteroatom?
a) Oxygen
b) Nitrogen
c) Carbon
d) Sulphur