Quick Organic Chem Nomenclature Question

[Batmaniac]

Homework Statement

I am to draw a structural diagram of 2,4-dimethyl-1-heptyne.

2. The attempt at a solution

----------CH3
CH=C-CH2-CH-CH2-CH2-CH3
---CH3

I tried just using spaces but it wouldn't indent them so I used hyphens. Now, I'm fairly certain my answer is correct (one of many possibilities) but I have a question about this compound. How can it have a methly group on 2 in addition to a triple bond? The 'C' in my diagram is sharing 3 electrons with the Carbon to its left, one with the carbon to its right, and one with the carbon below it. That totals to five shared electrons when Carbon wants 4. What's the deal?

 

[chemisttree]

You have an excellent grasp of the situation.

 

[Blueshift5]

I can confirm that your structural diagram of 2,4-dimethyl-1-heptyne is correct. The reason for the extra methyl group on carbon 2 is due to the concept of resonance in organic chemistry. In this case, the triple bond between the two carbon atoms can be delocalized, meaning that the electrons are shared between the two carbon atoms rather than being localized on one bond. This allows for the formation of the extra bond with the methyl group on carbon 2 without violating the octet rule for carbon. I hope this helps to clarify the structure and concept for you.