Question

The IUPAC name of Acrolein is:
A ) but-2-enal
B ) prop-2-enal
C ) but-3-enal
D ) 2-methyl prop-2-enal

Answer 1

The structural formula of acrolein is ${\text{C}}{{\text{H}}_2} = {\text{CH}} - {\text{CHO}}$. It contains an aldehyde functional group and one carbon-carbon double bond.

Complete answer:
The simplest unsaturated aldehyde is acrolein. The structural formula of acrolein is ${\text{C}}{{\text{H}}_2} = {\text{CH}} - {\text{CHO}}$. It contains three carbon atoms, an aldehyde functional group and one carbon-carbon double bond. The parent carbon chain contains three carbon atoms and is known as propane. Since one carbon carbon double bond is present, the suffix ‘-ane’ is replaced with the suffix ‘-ene’ to obtain propene. Since one aldehyde functional group is present, the suffix ‘-e’ is replaced with the suffix ‘-al’ to obtain propenal. The position of carbon carbon double bond is indicated by adding -2- before ‘enal’. When an aldehyde group is present in the molecule, the numbering is started from the aldehyde group.

The structural formula of ${\text{but - 2 - enal}}$ is ${\text{C}}{{\text{H}}_3} - {\text{C}}{{\text{H}}_2} = {\text{CH}} - {\text{CHO}}$. It contains four carbon atoms, a carbon-carbon double bond and an aldehyde group. The carbon-carbon double bond is present between the second and third carbon atom.
The structural formula of ${\text{but - 3 - enal}}$ is ${\text{C}}{{\text{H}}_2} = {\text{CH}} - {\text{C}}{{\text{H}}_2} - {\text{CHO}}$. It contains four carbon atoms, a carbon-carbon double bond and an aldehyde group. The carbon-carbon double bond is present between the third and fourth carbon atom.
The structural formula of ${\text{2 - methyl prop - 2 - enal}}$ is ${\text{C}}{{\text{H}}_2} = {\text{C}}\left( {{\text{C}}{{\text{H}}_3}} \right) - {\text{CHO}}$. It contains a chain of three carbon atoms, a carbon-carbon double bond, a methyl substituent and an aldehyde group. The carbon-carbon double bond is present between the second and third carbon atom.
The IUPAC name of Acrolein is ${\text{prop - 2 - enal}}$

Hence, the correct option is B ) ${\text{prop - 2 - enal}}$.

Additional Information: The name prop-2-enal can also be written as ${\text{ - 2 - propenal}}$ .

Note: Do not start the numbering from the end containing carbon-carbon double bond. When the aldehyde group is present in the parent chain, the numbering starts from the carbon atom of the aldehyde group. Most of the options in this question can be eliminated based on the number of carbon atoms. The number of carbon atoms in acrolein and ${\text{prop - 2 - enal}}$ is three each, whereas the remaining options have four carbon atoms each.