Question

Write structures for all the structural isomers of doublebonded compounds with the molecular formula \(\mathrm{C}_{5} \mathrm{H}_{10}\).

Short answer

Answer: There are three possible structural isomers of a double-bonded compound with the molecular formula C5H10. Their structures are as follows: 1. 1,2-disubstituted: H3C - CH = CH2 - CH2 - CH3 2. 2,3-disubstituted: H3C - CH2 - CH = CH2 - CH3 3. 3,4-disubstituted: H3C - CH2 - CH2 -CH = CH2

Step-by-step solution

Identify the longest carbon chain containing the double bond

We need to identify the longest continuous chain of carbon atoms containing the double bond. By default, we will have a 1,2-disubstituted alkene for the parent chain. The longest chain in this molecule will have 5 carbon atoms.

Draw the possible arrangements of double bonds between carbon atoms

In the first case, we will put the double bond between carbon 1 and carbon 2 (1,2-disubstituted). In the second case, we will place the double bond between carbon 2 and carbon 3 (2,3-disubstituted), and in the third case, between carbon 3 and carbon 4 (3,4-disubstituted). The position of the double bond between carbon 4 and carbon 5 would just be a mirror of the first isomer (1,2-disubstituted), so we don't need to consider it. This gives us three possible arrangements for the longest carbon chain.

Add the hydrogen atoms to each carbon atom

Each carbon has a valency of 4. The carbon atoms with double bonds will have one free valency for hydrogen, and the other carbon atoms will have two free valencies for hydrogens. Add hydrogen atoms accordingly to satisfy the valency of each carbon atom in each arrangement.

Draw the structures of the structural isomers

For each arrangement of the double bond and the longest carbon chain, draw the respective structures with all the hydrogen atoms attached. 1. 1,2-disubstituted (First arrangement): Structure: \(\displaystyle \mathrm{H}_{3} \mathrm{C} - \mathrm{CH} = \mathrm{CH}_{2} - \mathrm{CH}_{2} - \mathrm{CH}_{3}\) 2. 2,3-disubstituted (Second arrangement): Structure: \(\displaystyle \mathrm{H}_{3} \mathrm{C} - \mathrm{CH}_{2} - \mathrm{CH} = \mathrm{CH}_{2} - \mathrm{CH}_{3}\) 3. 3,4-disubstituted (Third arrangement): Structure: \(\displaystyle \mathrm{H}_{3} \mathrm{C} - \mathrm{CH}_{2} - \mathrm{CH}_{2} -\mathrm{CH} =\mathrm{CH}_{2}\) These are the three possible structures for all the structural isomers of a double-bonded alkene compound with the molecular formula \(\mathrm{C}_{5} \mathrm{H}_{10}\).