Answer
IUPAC nomenclature for the compounds (according to both old and new rules) is given below:
(a) Old: 2,2-Dimethyl-3-hexyne
or New: 2,2-Dimethylhex-3-yne
(b) Old: 2,5-Octadiyne
or New: Octa-2,5-diyne
(c) Old: 3,6-Dimethyl-2-hepten-4-yne
or New: 3,6-Dimethylhept-2-en-4-yne
(d) Old: 3,3-Dimethyl-1,5-hexadiyne
or New: 3,3-Dimethylhexa-1,5-diyne
(e) Old: 1,3-Hexadien-5-yne
or New: Hexa-1,3-dien-5-yne
(f) Old: 3,6-Diethyl-2-methyl-4-octyne
or New: 3,6-Diethyl-2-methyloct-4-yne
Work Step by Step
Rules to be followed while naming the compound:
1. Look for the longest hydrocarbon chain. It must include the triple bond. Incase two or more triple bonds are present, the longest chain is the one which includes all the triple bonds.
2. Start numbering the chain, starting at the end which is closest to the triple bond. Number all the substituents according to their position of attachment on the parent hydrocarbon chain. More than one substituents of the same kind use the prefix di-, tri-, tetra- etc depending on the number of same substituent groups. All the substituents are mentioned as prefixes to the parent chain.
If there is more than one substituent on a single carbon atom of the parent chain, then all the substituents are assigned the same number.
3. The hydrocarbon chain will have the suffix –yne (for alkynes). The presence of more than one triple bond is indicated by suffixing –diyne, -triyne, etc to the name of the parent chain.
4. If a molecule contains both double and triple bonds, the numbering of the chain will start from the end which is closest to the double or triple bond, whichever appears first.
5. While naming the compound, the substituents are written as prefixes (in alphabetical order) followed by the name of the parent chain and finally, the functional group is written as a suffix. Numbers are separated with the help of commas while a hyphen is used to separate numbers from alphabets.
6. Also, while writing the name of a compound containing multiple double or triple bonds, the position of the multiple bonds (assigned as number while numbering the chain) are also mentioned when writing the suffix.
