250+ TOP MCQs on Structural Representations of Organic Compounds and Answers

Chemistry Multiple Choice Questions on “Structural Representations of Organic Compounds”.

1. Identify the condensed formula of ethane from the following.
a) CH₃-CH₃
b) HC-H₂-C-H₃
c) CH₂=CH₂
d) CH₃CH₃
Answer: d
Clarification: In condensed formula, all the atoms are represented but single bonds are not shown. Only double and triple bonds will be represented. CH₂=CH₂ is not ethane; it is ethene.

2. Which is not a heteroatom?
a) Oxygen
b) Nitrogen
c) Carbon
d) Sulphur
Answer: c
Clarification: A heteroatom is any atom other than carbon or hydrogen atom. All the others apart from carbon mentioned above are heteroatoms. In other words, a heteroatom is a non-carbon atom present in a carbon structure.

3. No atoms are shown while representing structures in bond-line formula.
a) True
b) False
Answer: b
Clarification: Only carbon and hydrogen atoms are not shown in bond-line representation. But other atoms like oxygen, nitrogen, chlorine, etc. are shown. Bond-line representation of molecules is a skeletal representation in which the bonds are shown as single lines according to the bond order, i.e. one line for a single bond, two lines for a double bond and so on.

4. 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
Clarification: For determining the condensed formula, combine all the CH₂ terms together and assign the appropriate number to them, each time checking that carbon only forms four bonds with the other atoms. Here, in the first part, i.e. ClCH₂CH₂CH₂CH₂CHCH₂CH₂CH₂CHCH₂CH₃, there are four CH₂ terms; so we group all these terms and represent them as (CH₂)4. Similarly, combine the CH₂ terms in the other parts and eventually we get the condensed formula of the above mentioned molecule.

5. Determine the bond-line formula of CH₃CH₂COCH₂CH₃.
a)
b)
c)
d)
Answer: c
Clarification: In CH₃CH₂COCH₂CH₃, the ketone group(C=O) is attached to the third carbon and therefore the double bond should be represented at the end of the second line, i.e. at the position of the third carbon. In all the other options, the ketone group is not attached to the third carbon, thereby, making them incorrect.