Question

The IUPAC name of crotonaldehyde is:
A: prop-2-en-1-al
B: propenal
C: But-2-en-1-al
D: butenal

Answer 1

Hint: IUPAC stands for International Union of Pure and Applied Chemistry. It is the world authority on the chemical nomenclature as well as terminology. Thus, IUPAC nomenclature is basically a method of naming organic compounds according to certain rules.

Complete step by step solution:
Crotonaldehyde is a chemical compound having the chemical formula as $ C{H_3}CH = CHCHO $ . The chemical structure of crotonaldehyde is shown below:

IUPAC provides consistency to the names of organic compounds. It enables every compound to possess a unique name, which otherwise is not plausible with the common names. Now, let us have a look at the important rules that need to be followed during naming of a compound:
To determine the prefix or suffix of the compound name, recognise the functional group present in the compound (as listed in table).

Functional group	Prefix or Suffix
Alkane	-ane
alkene	-ene
Alkyne	-yne
Alcohol	-ol
Aldehyde	-al
Ketone	-one
Carboxylic acid	-oic acid
ester	-oate
ether	Alkoxy-
Haloalkane	Halo-

The given compound i.e. crotonaldehyde is an alkene with the presence of an aldehydic group so suffix in our case will be $ (-ene) + ( - al) = - enal $ .
To determine the name of a compound, identify the longest and continuous chain of carbon containing the functional group and count the number of carbon atoms in the chain as shown in the table below.

Number of carbon atoms	Prefix
1	Meth-
2	Eth-
3	Prop-
4	But-
5	Pent-
6	Hex-
7	Hept-
8	Oct-
9	Non-
10	Dec-

In the given compound, the number of carbon atoms in the longest chain is 4. That means the prefix of alkane in our case is But-.
Numbering of the carbons in the longest chain of carbon (Remember that If the organic molecule is not an alkane (and has a functional group) you have to initiate numbering such that the functional group is placed on the carbon having the lowest possible number).
In the given compound, we can number as shown below:

It is clear that the aldehydic group is present on the first carbon and $ - C = C - $ are present on the second carbon.
Check if there are any branched groups, name them and allocate the number of the carbon atom to which that group is linked. The branched groups must be mentioned before the name of the main chain in an alphabetical order.
In the given compound, no branched group is present.
Finally, combine the elements of the compound name in the specified order as: branched groups, prefix, suffix according to the functional group and its location along the longest carbon chain.
Therefore, the given compound will have IUPAC name as: But-2-en-1-al.
Hence, the correct answer is Option C.

Note:
IUPAC nomenclature creates a standardized method to name the chemical compounds. Common nomenclature employs the older names for organic compounds rather than using the prefixes for the carbon chain. IUPAC nomenclature even provides certain rules for the naming of ions as well.