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why are alkoxides better bases than alkyl sulfides?
why are alkoxides better bases than alkyl sulfides?
- Thread starter OneManShow
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I think it's easiest to look at conjugate acid strength to explain why the alkoxide is the stronger base:
R-OH vs. R-SH:
Sulfur is larger than oxygen, so the bond to hydrogen is weaker. Thus it is the stronger acid (more likely to give up the hydrogen). This is always true as you go down a group (acidity increases down a group).
The stronger conjugate acid correlates to the weaker base. R-OH is the stronger base as it has the weaker conjugate acid.
Hope this explanation makes sense.
R-OH vs. R-SH:
Sulfur is larger than oxygen, so the bond to hydrogen is weaker. Thus it is the stronger acid (more likely to give up the hydrogen). This is always true as you go down a group (acidity increases down a group).
The stronger conjugate acid correlates to the weaker base. R-OH is the stronger base as it has the weaker conjugate acid.
Hope this explanation makes sense.
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Think of it in terms of acidity and you'll find the answer just as well. Oxygen and sulfur are in the same column of the periodic table. As we descend the column our atom gets larger which means that when it bears a negative charge (ie as a result of deprotonation) the negative charge is more spread out, leading to a more stable anion. In general, the more "spread out" (or diffuse) a negative charge is the less basic our species will be. Localized charges are seen to be most basic because they are more able to "hone" in and abstract a hydrogen. All of this equates to sulfhydryls being more acidic than alchohols, and therefore sulfides are weaker bases than alkoxides.
Does that make sense?
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yes thanks !
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