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In Peter Sykes' A Guidebook to Mechanism in Organic Chemistry, it says that sp3 orbitals have greater relative overlap compared to sp bonds.

We know that the $\ce{C-H}$ bond is shorter in ethyne compared to ethane. So the intuitive idea that more overlap would lead to stronger bond formation is obviously incorrect.

So what is the relation between relative overlap of two orbitals and their bond strength? Is there any use that we can get from this overlap?

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    $\begingroup$ I think there is just one counterpart missing. Greater overlap.... to what? $\endgroup$
    – Alchimista
    Jun 18, 2020 at 12:11
  • $\begingroup$ @Alchimista, I think it would be to another similar orbital. Probably sp3 with sp3 vs sp with sp. But that still implies that the C-C bond in ethane should be stronger then the C-C bond in ethyne with is incorrect. I have added a link to the relevant portion of the text $\endgroup$
    – gauri agrawal
    Jun 19, 2020 at 8:03
  • $\begingroup$ You see that it mentions one C and four H atoms.... To your note: likely one single C-C bond is stronger in ethane vs ethyne, tough difference might be small and other consideration could be made (eg the relevant region is crowded with electrons) but I do not knoe/forgot. If we touch the yne portion of the molecule, we normally don't go down to total breaking.... $\endgroup$
    – Alchimista
    Jun 19, 2020 at 8:39
  • $\begingroup$ @Alchimista I think the text just wants to explain why hybridization happens in the first place, why all the CH bonds are equal in methane, or why O atoms are sp3 hybridized instead of sp. $\endgroup$
    – gauri agrawal
    Jun 19, 2020 at 11:28
  • $\begingroup$ In that context is straightforward $\endgroup$
    – Alchimista
    Jun 20, 2020 at 13:54

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I suppose the author was talking about the internal overlap which takes place while the formation of sp and sp3 hybrid orbitals.

What I mean is when one s and one p orbital overlap, the extent of overlapping is less than the overlap that happens when one s and three p orbitals overlap. To understand it more easily, suppose a ball represent a s orbital while a pencil represent p orbital. Think in mind the extent overlap of three pencils and one ball will be more than the extent of overlap of one pencil and one ball.

But the situation changes, when you overlap two sp3 orbitals or two sp orbitals. sp having more s character is relatively stronger then sp3, thus c-c bond is stronger in ethyne than ethane.

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    $\begingroup$ The text clearly states that we are talking about overlapping of an atomic orbital from each of the participating atoms $\endgroup$
    – gauri agrawal
    Jun 21, 2020 at 3:27

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