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I have problem here So I had learn that the percent of s-character of hybrid orbital will affect the bond strength. The higher percentage of s-character,the stronger the bond.For example the strength C-H in ethane(sp3,25%) is the weakest followed by in ethene(sp2,33%) and strongest in acetylene(sp,50%)

The percentage of s-character of the hybrid orbital also affect the acidity.The higher the percentage of s-character,the stronger the acidity. The reason here is that the conjugated base formed is more stable as the electron is in lower energy and pulled nearer to the nucleus of the atom.For example, acidity hydrogen ion in C-H for compound ethane is weakest followed by ethene and acetylene being the most acidic.

But isn't the C-H bond strength in the acetylene is the strongest.So it should be hard for acetylene to loss it hydrogen. So why isn't the acetylene being the least acidic? Can someone explain to me?

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  • $\begingroup$ The carbon in ethyne is very much electrophilic compared to ethane/ethene. $\endgroup$ Oct 26, 2023 at 3:48
  • $\begingroup$ Ya, I know about this,but as I stated in the last paragraph, the strength C-H in ethyne is the strongest among the three. So, isn't the H+ is harder to release from C-H in ethyne. Or this effect is not strong and can be ignored? $\endgroup$
    – Sheng Lee
    Oct 26, 2023 at 5:17
  • $\begingroup$ Take the hydrogen halide as example.The bond length of H-A where A is halogen(Cl,Br and I) increase down the group,hence the H-A bond strength decrease down the group and so the acidity of hydrogen hallide increase down the group. $\endgroup$
    – Sheng Lee
    Oct 26, 2023 at 5:32
  • $\begingroup$ Yes, it's stronger, but it's means that energy of homolytic cleavage is higher, not heterolytic - that's what happens in acid base reactions. $\endgroup$
    – Mithoron
    Oct 26, 2023 at 18:47
  • $\begingroup$ Ok after seeing the other post ans, I get it now. Tqvm $\endgroup$
    – Sheng Lee
    Oct 27, 2023 at 0:05

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