How to Draw All the Isomers of an Organic Compound with a Given Molecular Formula – Part 1

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 C4H8?

Solution infographic:



Click/tap 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.

# Draw the C-atoms of the parent chain right to left keeping enough space between the atoms so that the bonds and the H-atoms with their indices may be inserted later.

# Draw single bonds between the C-atoms keeping the bonds close to the right of the pair each time.

# 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 pair.

Or,

For only one functional group (say, halogen) in the molecule: Place a single bond vertically on top of the rightmost C-atom and then place the functional group on top of that bond.

# Place a single bond vertically on top of the next to the rightmost C-atom and then place the alkyl locant on top of that bond. Make sure that the number of C-atoms in the parent chain must not be exceeded by doing so.

# Introduce the H-atoms as required. The H-atom with its index should be left to the leftmost C-atom and that be right to the rightmost C-atom.

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.

Isomers isolated❓ Let Chemaficionado know in the comments below or 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.

Comments

Post a Comment

Popular posts from this blog

How to Predict where an Electrophilic Aromatic Substitution May Occur in a Ring – Part 3

Image
An organic reaction in which an atom attached to an aromatic system (usually hydrogen) is substituted by an electrophile is referred to as  electrophilic aromatic substitution  ( S E Ar  or  EAS ). One of the most important  EASs  is halogenation. If Bromine water is added to Aniline, a multi-substituted product ( 2,4,6 -derivative) is obtained as Aniline is a strongly activating group (the same happens to Phenol). To generate the mono-substituted product, a protection, say, an acyl group is required. Question: Predict the major product(s) of the following reaction: Click/tap to enlarge the image Solution infographic: Click/tap to enlarge the image Motivated by EAS ❓ Let Chemaficionado know  in the comments below or at mychemistryhomework@gmail.com ❗ References: (1)      Wikipedia Contributors.  Electrophilic aromatic substitution . Wikipedia. https://en.wikipedia.org/wiki/Electrophilic_aromatic_substitution. (2)    ...
Read more

How to Carry out a Multistep Synthesis – Part 4

Image
Multistep synthesis  is the artificial execution of multiple organic chemical reactions to obtain one or more products by physical and chemical manipulations. Retrosynthetic analysis is a problem-solving approach in the organic syntheses, achieved by transforming a target molecule into simpler precursor structures regardless of any potential reactivity/interaction with reagents, and repeated until a simple or commercially available structure is reached, which can be used as a starting material to synthesize the target molecule. Question: How would you do the following transformation? Click/tap here to enlarge the image Solution infographic: Click/tap here to enlarge the image Let's keep in mind that any multistep synthesis is possible via several routes ❗Questions ❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com ❗ References: (1)      Wikipedia Contributors.  Chemical synthesis . Wikipedia. https://en.wikipedia.org/wiki/Chemi...
Read more

How to Predict where an Electrophilic Aromatic Substitution May Occur in a Ring – Part 8

Image
An organic reaction in which an atom attached to an aromatic system (usually hydrogen) is substituted by an electrophile is referred to as  electrophilic aromatic substitution  ( S E Ar  or  EAS ). One of the most important  EASs  is nitration . Let's keep in mind that the presence of an activating group on the ring may complicate nitration. Question: Predict the major product(s) of the following reactions: Click/tap to enlarge the image Solution infographic: Click/tap to enlarge the image Eerie EAS chemistry❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com ❗ References: (1)      Wikipedia Contributors.  Electrophilic aromatic substitution . Wikipedia. https://en.wikipedia.org/wiki/Electrophilic_aromatic_substitution. (2)      Brown, C.; Ford, M.  Higher Level Chemistry , 2nd ed.; Pearson Education: Harlow, Essex, 2014. ‌(3)     Electrophilic aromatic directing gro...
Read more