26E
Question
Draw and name the six possible diene isomers of formula. Which of the six are conjugated dienes?
Step-by-Step Solution
VerifiedDienes are the unsaturated compounds containing two double bonds between carbon atoms. Dienes are used in organic synthesis and as monomers in polymer industry. Based on the position of double bonds in the whole molecule, dienes are of three types-
- Cumulated dienes
- Conjugated dienes
- Isolated dienes
Cumulated dienes
When two double bonds are present successively on adjacent carbons, cumulated dienes are constituted. They are also called as allenes.
Conjugated Dienes
Dienes having two conjugated double bonds which are separated by a single bond, are called conjugated dienes.
Isolated Dienes
When double bonds in the molecule are separated by more than one single bond, it is isolated diene.
Chemical compounds which have identical chemical formula but have different chemical structures, different properties, are known to be exhibiting isomerism. Therefore, the compounds which exhibit isomerism are called isomers.
It is of two types- structural and stereoisomerism. Here we will be talking about structural isomerism. In structural isomerism the constituent atoms are linked in different ways in each isomer. For example- Alkane with formula can have three isomers, showing chain isomerism ( type of isomerism where the molecular formula of isomers is same but they have different length of C chains).
Since, it is diene, 2 double bonds are there. So we will first draw the carbon skeleton which is of 5.
c-c-c-c-c
Now, start placing two double bonds in the molecule, each time changing the position of double bonds. This way we get following isomers with formula .
As we know that in conjugated dienes the double bonds are separated by a single bond. Of all the structures proposed in step 3 two are conjugated dienes namely, 1,3-pentadiene and 2-methyl-1,3-butadiene.