Question

The correct answer is either a or d. Can anyone explain which one it is and why? CH3C ≡ CCH2CH2Cl is named: a. 1-chloro-3-pentyne b. 5-chloro-2-pentene c. 1-acetylenyl-3-chloropropane d. 5-chloro-2-pentyne

Answer 1

Answer: The IUPAC name of $CH_3C\equiv CCH_2CH_2Cl$ is 5-chloro-2-pentyne

Explanation:

1. First select the longest possible carbon chain.  For the number of carbon atom, we add prefix as 'meth' for 1, 'eth' for 2, 'prop' for 3, 'but' for 4, 'pent' for 5, 'hex' for 6, 'sept' for 7, 'oct' for 8, 'nona' for 9 and 'deca' for 10.

2. The longest possible carbon chain should contain all the bonds and functional groups.

3. The numbering is done in such a way that the carbon containing the functional group or substituent gets the lowest number.

4. The naming of alkane is done by adding the suffix -ane, alkene by adding the suffix -ene, alkyne.

Thus the IUPAC name of $CH_3C\equiv CCH_2CH_2Cl$ is 5-chloro-2-pentyne