Question

The IUPAC name of the crotonaldehyde is

A.2-Propenal
B.Propenal
C.2-Butenal
D.Butenals

Answer 1

Hint: The molecular formula of crotonaldehyde is ${{\text{C}}_{\text{4}}}{{\text{H}}_{\text{6}}}{\text{O}}$ . It is an unsaturated aldehyde. Crotonaldehyde is the common name of the compound. Use the IUPAC rules to determine the IUPAC name of the compound.

Step by step answer: The molecular formula of crotonaldehyde is ${{\text{C}}_{\text{4}}}{{\text{H}}_{\text{6}}}{\text{O}}$ and its structure is as follows:

Using the IUPAC rule determines the IUPAC name of the crotonaldehyde.

Rule1. Determine the longest continuous chain (parent chain) of carbon atoms.

In the structure of crotonaldehyde, the longest continuous chain contains 4 carbon atoms.

Rule 2. Number the chain in such a way that the functional group will get the lowest priority.

In crotonaldehyde, aldehyde is the functional so number the parent chain from the carbon atom where the carbonyl group ${\text{(C = O)}}$ is bonded.

As the parent chain contains 4 carbon atoms with aldehyde functional group so the root name of the compound is butanal. However, the compound also contains ${\text{C = C}}$ at position 2 so the IUPAC name of the crotonaldehyde is 2-butenal.

As the longest continuous chain contains 4 atoms so option (A) 2-Propenal is incorrect as it indicates the parent chain contains 3 carbon atoms.

Similarly, option (B) Propenal is also incorrect as it indicates; the parent chain contains 3 carbon atoms.

Option (D) Butenals is incorrect as the position of the double bond is not mentioned in the name of the compound.

Thus, the correct option is (C) 2-butenal.


Note: The IUPAC naming is the systematic approach of naming the compounds. Few IUPAC rules are common for all compounds while few rules get changed as per the functional groups. In general, the IUPAC system of naming an organic compound consists of prefix and suffix. The prefix depends on the number of carbon atoms present in a parent chain and the suffix denotes the functional group present in the compound. If there is more than one functional group like aldehyde and alkene in this case use the suffix of a functional group having the highest priority.