How to Draw All the Isomers of an Organic Compound with a Given Molecular Formula – Part 2

Isomers are different compounds that have the same molecular formula.


When the group of atoms that form the molecules of different isomers are bonded together in fundamentally different ways, constitutional/structural isomers are formed.

Isomers that differ only in the spatial orientation/configuration of their component atoms are referred to as stereoisomers or spatial isomers.

Question:

How many isomers (including stereoisomers) do exist with the molecular formula C5H10?

Solution infographic:



Click to enlarge the image

MF = Molecular formula, DBE = Double bond equivalent, DU = Degree of unsaturation, IHD = Index of hydrogen deficiency

Tip for drawing the parent hydrocarbon chain: The beginners are encouraged to use the condensed structural formulae for a better understanding. For a guide, please click here. The following guide is applicable to the bond-line or skeletal structural formulae.

# Draw the parent chain in a zigzag pattern.

# For only one double/triple bond in the molecule: Change the single C─C bond to a double C=C bond (or triple C≡C bond) for the rightmost bond-line.

Or,

For only one functional group (say, halogen) in the molecule: Connect a single bond to the right of the right terminus keeping the zigzag pattern and then place the functional group next to the new terminus.

# Connect a single bond vertically to the top (or bottom) of the left of the rightmost bond-line if the locant is methyl. If the locant has more than one carbon, add more bone-lines in a zigzag way. Make sure that the number of C-atoms in the parent chain must not be exceeded by doing so.

The next isomers may be generated by moving the double/triple bond (or the functional group) and/or the alkyl locant from the right to the left in the parent chain. Make sure that a constitutional isomer is created by that shift (Hint: For all constitutional isomers, each different compound has a different IUPAC name). Look for stereocenters so that the presence of stereoisomers is not overlooked.

Inspiring isomers❓ Let Chemaficionado know at mychemistryhomework@gmail.com❗

References:

(1)    Structural isomer. Wikipedia. https://en.wikipedia.org/wiki/Structural_isomer.

(2)    Stereoisomerism. Wikipedia. https://en.wikipedia.org/wiki/Stereoisomerism.

(3)    Stereocenter. Wikipedia. https://en.wikipedia.org/wiki/Stereocenter.
(4)    Wikipedia Contributors. IUPAC nomenclature of organic chemistry. Wikipedia. https://en.wikipedia.org/wiki/IUPAC_nomenclature_of_organic_chemistry.‌

(5)    Chouhan, M. S. Advanced Problems in Organic Chemistry for JEE, 11th Ed.

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