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How do I find the total number of “hyperconjugable” structures for 1-(3-ethyl-4-methylphenyl)-2-methylprop-1-ylium?

1-(3-ethyl-4-methylphenyl)-2-methylprop-1-ylium

I read some sources stating that the total number of “hyperconjugable” structures is equal to the total number of α-hydrogen atoms. But which carbon is taken as the alpha carbon in a compound having no functional groups, just carbons?

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  • $\begingroup$ How many hydrogens "contribute to hyperconjugation" is more understandable phrasing. $\endgroup$ – orthocresol Sep 23 at 16:57
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There is one obvious $\alpha$-position, which is the tertiary carbon atom adjacent to the carbon carrying positive charge. This contributes one hypercongujation structure. It looks like there are no more apparent structures, but the methyl group that is para to the cation can also participate in hyperconjugation

hyperconjugation structure

There are three $\ce{H}$-atoms on the methyl group, which give us three more structures. Thus, there are a total of 4 hyperconjugable hydrogens in this structure.

Interesting to note is that the ethyl group at the meta position does not participate in hyperconjugation. Can you find a reason why?

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