Question

What is the structure for 3,4-dimethylpent-4-en-1-yne and 2,3-dimethylpent-1-en-4-yne?

Answer 1

These are the same compound.

Explanation:

3,4-Dimethylpent-4-en-1-yne

The base name -pent- tells you that you have a 5-carbon chain.

(from opsin.ch.cam.ac.uk)

The -4-en-1-yne suffixes tell you that there is a `"C=C"` double bond between `"C-4"` and `"C-5"` and a `"C≡C"` triple bond between `"C-1"` and `"C-2"`.

(from opsin.ch.cam.ac.uk)

The 3,4-dimethyl- prefix tells you that there is a methyl group on C-3 and one on C-4.

(from opsin.ch.cam.ac.uk)

NOTE: This is not the correct IUPAC nomenclature.

You number the bonds first, then you add the methyl groups.

-ene takes numbering priority over -yne when there is a choice in numbering.

This could be either -1-en-4-yne or -4-en-1-yne, so we have a choice.

The first ending takes priority, so the correct IUPAC name is 2,3-dimethylpent-1-en-4-yne.