Acid Strength and Hybridization

[karkatvantas]

I was hoping someone here might be able to clarify this little conceptual conundrum I'm having:

I understand that larger atoms will produce stronger acids than smaller atoms in the same group, such as H-Br vs H-F, because the negative electric charge is distributed through more space in the anion Br-.

Why then is it that an for hybridization, acid strength is sp > sp2 > sp3 ?

Hybrid orbitals that have more s character are smaller, so the negative electric charge on the conjugate base is more tightly concentrated in the case of an sp hybridized orbital than in the case of an sp3 hybridized orbital. Doesn't this logic contradict the reasoning for larger atoms being stronger acids?

I understand that the strength of an acid comes from the ability of the conjugate base to stabilize its negative charge, but I don't understand why an sp hybridized atom is more stabilizing than an sp3 hybridized atom.

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[PiBond]

I was hoping someone here might be able to clarify this little conceptual conundrum I'm having:

I understand that larger atoms will produce stronger acids than smaller atoms in the same group, such as H-Br vs H-F, because the negative electric charge is distributed through more space in the anion Br-.

Why then is it that an for hybridization, acid strength is sp > sp2 > sp3 ?

Hybrid orbitals that have more s character are smaller, so the negative electric charge on the conjugate base is more tightly concentrated in the case of an sp hybridized orbital than in the case of an sp3 hybridized orbital. Doesn't this logic contradict the reasoning for larger atoms being stronger acids?

I understand that the strength of an acid comes from the ability of the conjugate base to stabilize its negative charge, but I don't understand why an sp hybridized atom is more stabilizing than an sp3 hybridized atom.

electrons in an s orbital are lower in energy than those in a p orbital and are held more tightly to the nucleus. thus, the more s character in a hybrid orbital the more electronegative the atom will be and the more acidic its bond to hydrogen will be

 

[ilovemcat]

I was hoping someone here might be able to clarify this little conceptual conundrum I'm having:

I understand that larger atoms will produce stronger acids than smaller atoms in the same group, such as H-Br vs H-F, because the negative electric charge is distributed through more space in the anion Br-.

Why then is it that an for hybridization, acid strength is sp > sp2 > sp3 ?

Hybrid orbitals that have more s character are smaller, so the negative electric charge on the conjugate base is more tightly concentrated in the case of an sp hybridized orbital than in the case of an sp3 hybridized orbital. Doesn't this logic contradict the reasoning for larger atoms being stronger acids?

I understand that the strength of an acid comes from the ability of the conjugate base to stabilize its negative charge, but I don't understand why an sp hybridized atom is more stabilizing than an sp3 hybridized atom.

There's two ways to look at the relative strengths of the haloacids. Going down a column, halogen size increases and so upon deprotonation the conjugate base would be more stabilized due to the larger electron cloud (ie. it's more polarizable). However, a different perspective is the bond itself - not only is the conjugate base more stabilized as the anion increases in size, but the bond itself is longer and because it's longer it's easier to deprotonate.

With regard to hybridization, now it would seem that they're telling you that stronger bonds are more acidic... which is slightly confusing. However this is all relative. It's more acidic than an sp2 or sp3 hybridized atom. An sp hybridized atom though is still weakly acidic and therefore would require a relatively strong base to deprotonate it. In this case though, it's more acidic than say an sp2 or sp3 hybridized atom because the conjugate base is more stabilized on an sp hybridized atom than an sp2 or sp3 hybridized atom. I guess you could say that stability is much more significant the bond length now. An sp hybridized atom has more "s character," and so it can support the extra negative charge better. In other words, it pulls the electron density closer towards the central region (near the nucleus) than an sp2 or sp3 hybridized atom.