Question

Determine the IUPAC name of cinnamaldehyde.
A. $2\left( {\text{E}} \right) - 3 - {\text{phenlyprop}} - 2 - {\text{enal}}$
B. $2\left( {\text{Z}} \right) - 1 - {\text{phenlyprop}} - 1 - {\text{enal}}$
C. $2\left( {\text{E}} \right) - 1 - {\text{phenlyprop}} - 2 - {\text{enal}}$
D. $2\left( {\text{E}} \right) - 3 - {\text{phenlyprop}} - 1 - {\text{enal}}$

Answer 1

Hint: Cinnamaldehyde is an organic compound having a chemical formula ${{\text{C}}_{\text{6}}}{{\text{H}}_{\text{5}}}{\text{CH = CHCHO}}$. The structure has one phenyl group and a functional group that is enal.

Complete step by step answer:
The structure of cinnamaldehyde is as follows:

To give the IUPAC name, select the longest carbon chain.
Determine the substituents and give numbering to chain as so, all the group get minimum numbering.
Give the numbering to the carbon atoms of the chain so, all the groups get minimum numbering.
Arrange the group in alphabetical order. For this check base name of the group, not the prefix.

Select the longest carbon chain as follows:

The longest carbon chain is of three carbon atoms. The three carbon atoms chain is known as ‘prop’.

The $\alpha ,\beta $ unsaturated aldehyde is known as ‘enal’.

At carbon number-3, the phenyl group is present and carbon number-2, enal group is present.

Determine the stereochemistry at double bond as follows:

If the same priority groups at the double bond are on the same side the stereochemistry at the double bond is Z.
If the same priority groups at the double bond are on the opposite side the stereochemistry at the double bond is E.

Both the same priority hydrogens at the double bond in cinnamaldehyde are on opposite sides, so the stereochemistry at carbon number-2 will be E.

So, the name IUPAC name of the cinnamaldehyde is $2\left( {\text{E}} \right) - 3 - {\text{phenlyprop}} - 2 - {\text{enal}}$.

Thus, the correct option is A$.


Note:
Stereochemistry at double bond can also be determined if both carbon atoms of the double bond have different groups. In that case, if the high molecular weight groups are on the same side the stereo will be Z and if the high molecular weight groups are on the opposite side the stereo will be E.