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Why is sodium methanethiolate still a better nucleophile than sodium methoxide when the solvent is ethanol
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Kevin Counihan
Why is sodium methanethiolate still a better nucleophile than sodium methoxide when the solvent is ethanol
Thiolates are generally more nucleophilic than alcoholates. So whenever the choice happens to be between a nucleophilic sulphur and a nucleophilic oxygen, the sulphur will win.
Both the methanolate and the methanethiolate will show reduced nucleophilicity due to partial protonation, though. And of course you have introduced ethanolate as an additional nucleophile, too (which should be the least reactive, though).
Thiolates are generally more nucleophilic than alcoholates. So whenever the choice happens to be between a nucleophilic sulphur and a nucleophilic oxygen, the sulphur will win.
Both the methanolate and the methanethiolate will show reduced nucleophilicity due to partial protonation, though. And of course you have introduced ethanolate as an additional nucleophile, too (which should be the least reactive, though).
Nucleophiles can be hard or soft (as can electrophiles); a hard nucleophile tends to react preferentially with a hard electrophile, while a soft nucleophile tends to react preferentially with a soft electrophile.
In your system the methanethiolate anion, $\ce{CH3S-}$, is a soft nucleophile while methoxide, $\ce{CH3O-}$, is a relatively hard nucleophile. You will also have ethoxide ($\ce{CH3CH2O-}$) in your system. As to the electrophile, methyl iodide, $\ce{CH3I}$: it is soft and hence it preferentially reacts with the softer nucleophile in the system, methanethiolate.
A more sophisticated explanation of the hard/soft idea can be found in frontier orbital analysis.
Nucleophiles can be hard or soft (as can electrophiles); a hard nucleophile tends to react preferentially with a hard electrophile, while a soft nucleophile tends to react preferentially with a soft electrophile.
In your system the methanethiolate anion, $\ce{CH3S-}$, is a soft nucleophile while methoxide, $\ce{CH3O-}$, is a relatively hard nucleophile. You will also have ethoxide ($\ce{CH3CH2O-}$) in your system. As to the electrophile, methyl iodide, $\ce{CH3I}$: it is soft and hence it preferentially reacts with the softer nucleophile in the system, methanethiolate.
A more sophisticated explanation of the hard/soft idea can be found in frontier orbital analysis.
badly describe this case and shouldn’t be pulled into this argument. Remember that the HSAB concept originally intended to explain the formation of stable More
Thiolates are generally more nucleophilic than alcoholates. So whenever the choice happens to be between a nucleophilic sulphur and a nucleophilic oxygen, the sulphur will win.
Both the methanolate and the methanethiolate will show reduced nucleophilicity due to partial protonation, though. And of course you have introduced ethanolate as an additional nucleophile, too (which should be the least reactive, though).
Thiolates are generally more nucleophilic than alcoholates. So whenever the choice happens to be between a nucleophilic sulphur and a nucleophilic oxygen, the sulphur will win.
Both the methanolate and the methanethiolate will show reduced nucleophilicity due to partial protonation, though. And of course you have introduced ethanolate as an additional nucleophile, too (which should be the least reactive, though).
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Nucleophiles can be hard or soft (as can electrophiles); a hard nucleophile tends to react preferentially with a hard electrophile, while a soft nucleophile tends to react preferentially with a soft electrophile.
In your system the methanethiolate anion, $\ce{CH3S-}$, is a soft nucleophile while methoxide, $\ce{CH3O-}$, is a relatively hard nucleophile. You will also have ethoxide ($\ce{CH3CH2O-}$) in your system. As to the electrophile, methyl iodide, $\ce{CH3I}$: it is soft and hence it preferentially reacts with the softer nucleophile in the system, methanethiolate.
A more sophisticated explanation of the hard/soft idea can be found in frontier orbital analysis.
Nucleophiles can be hard or soft (as can electrophiles); a hard nucleophile tends to react preferentially with a hard electrophile, while a soft nucleophile tends to react preferentially with a soft electrophile.
In your system the methanethiolate anion, $\ce{CH3S-}$, is a soft nucleophile while methoxide, $\ce{CH3O-}$, is a relatively hard nucleophile. You will also have ethoxide ($\ce{CH3CH2O-}$) in your system. As to the electrophile, methyl iodide, $\ce{CH3I}$: it is soft and hence it preferentially reacts with the softer nucleophile in the system, methanethiolate.
A more sophisticated explanation of the hard/soft idea can be found in frontier orbital analysis.
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