34. The IUPAC name of the compound is ________.
(1) 3-keto-2-methylhex-4-enal
(2) 5-formylhex-2-en-3-one
(3) 5-methyl-4-oxohex-2-en-5-al
(4) 3-keto-2-methylhex-5-enal
Answers
Answer:
1. 3-keto 2-methylhex-4en 2-al
The IUPAC name of the given compound is 3-keto-2-methylhex-4-enal. Hence, option (A) is correct.
• Two functional groups are present in the compound, one being the aldehyde (CHO) group, and the other being the keto (C=O) group.
• The CHO group lies above the C=O group in the seniority table, and is therefore, given preference in the nomenclature of a compound.
• The numbering of the carbon chain, thus, starts from the CHO group and the carbon of the same is marked as 1.
• Next, we see that, at the second crabon, a methyl group is attached. Therefore, it is written as "2-methyl" in the nomenclature.
• The C=O group is attached at the fourth carbon. Being lower than CHO in the seniority table, it is written as the "keto" group in nomenclature, and not as 'one'.
• The double bond is named as "ene" with the number of the first carbon in the bond (4-ene).
• The number of carbon atoms present in the straight chain of the compound is 6, denoted by the prefix "hex".
• Since CHO is the seniormost functional group in the compound, it is denoted by the suffix "al" in the nomenclature.
• It should also be noted that the side chain groups in a compound are always represented alphabetically in a nomeclature. 'K' comes before 'm' in the alphabetical series, therefore, "3-keto" is written before "2-methyl" in the nomenclature.
• At last, but not the least, we must keep in mind that the vowel at the end of the name of a group or bond should be omitted if the name of the group or bond following it starts with a vowel too. This is why, in this compound, '4-ene' and 'al' are written together as "4-enal", and not as '4-eneal'.
• Following all the rules of nomenclature, "3-keto-2-methylhex-4-enal" is the correct IUPAC name for the given compound.