Question

Which of the following is not a correct IUPAC name?
1)2-methyl-2-propanol
2) pent-3-ene
3) 3-methylbutanone
4) 2-chlorobutanal

Answer 1

IUPAC stands for international union for pure and applied chemistry. It has made certain rules for naming of chemical compounds.

Complete answer:
IUPAC has made rules regarding naming of organic compounds. Some of the main rules include:
-the longest carbon chain is selected for giving the numbers to the carbon atoms. The chain can be zig-zag.
- numbering is started from the carbon which is nearest to the substituted carbon.
- numbering is done from that carbon which is near to the functional group.
- Presence of more than two side chains is written alphabetically.
- writing of the prefixes ‘iso’ and ‘neo’ is considered to be a part of alkyl group when writing in alphabetical order . While ‘sec’ and ‘tert’ are not.
Through the above mentioned major points of naming, the names given, 2-methyl-2-propanol, 3-methylbutanone, and 2-chlorobutanal are correct.
While, the name, pent-3-ene is not correct. As, through the nomenclature rules, we know that, numbering of the carbon chain is done in the manner that the substituted carbon, or carbon with double, or triple bond is near to the starting of numbering.
As the name pent-3-ene states that double bond is on the third position. It can be written correctly as pent-2-ene, which has a double bond near to the first carbon.

Hence, option 2) is correct; pent-3-ene is the incorrect IUPAC name.

Note:
The longest chain decided for numbering of the carbons is called the parent chain. The numbering is started as to have the lowest number between any substituent on the carbon.