why is CH3SH a better nucleophile than C2H5OH? I thought that following CARDIO, for A--> you first look at size and then at EN. S is LARGER than O, doesn't that make O more favorable since it is smaller and therefore less stable? (even though O is more EN than S).
Nuc Strength
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wait i think i can answer my own question.
It's b/c CARDIO is only for Acids/Bases and for nucs, you look at EN and not at size. therefore, since S is LESS EN than O, it makes it less stable and thus a better nuc.
right?
It's b/c CARDIO is only for Acids/Bases and for nucs, you look at EN and not at size. therefore, since S is LESS EN than O, it makes it less stable and thus a better nuc.
right?
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Nucleophile strength in aprotic solvent follows the trend you mentioned (stronger going up the periodic table as size gets smaller and charge is less stabilized, and stronger to the left across the periodic table since it's less electronegative) - but what is often not mentioned is that this trend applies specifically to negatively charged nucleophilic atoms. Neutral (uncharged) nucleophiles are stronger going down the periodic table - since both nucleophiles you mentioned are neutral, and S is the larger atom, it is the stronger nucleophile.
The reason for this (I doubt you need to know this level of detail for the DAT, but here it is anyway):
"What happens as we move up and down a column when considering uncharged nucleophiles? It turns out that, in the case of uncharged nucleophiles, size dictates nucleophilicity. This is because larger elements have bigger, more diffuse, and more polarizable electron clouds. This cloud facilitates the formation of a more effective orbital overlap in the transition state of bimolecular nucleophilic substitution (SN2) reactions, resulting in a transition state that is lower in energy and a nucleophilic substitution that occurs at a faster rate."
Source: http://chemwiki.ucdavis.edu/Organic_Chemistry/Reactions/Substitution_Reactions/SN2/Nucleophile
The reason for this (I doubt you need to know this level of detail for the DAT, but here it is anyway):
"What happens as we move up and down a column when considering uncharged nucleophiles? It turns out that, in the case of uncharged nucleophiles, size dictates nucleophilicity. This is because larger elements have bigger, more diffuse, and more polarizable electron clouds. This cloud facilitates the formation of a more effective orbital overlap in the transition state of bimolecular nucleophilic substitution (SN2) reactions, resulting in a transition state that is lower in energy and a nucleophilic substitution that occurs at a faster rate."
Source: http://chemwiki.ucdavis.edu/Organic_Chemistry/Reactions/Substitution_Reactions/SN2/Nucleophile
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Sulfur is one of the BEST nucleophiles,,,,,,,This atom is fairly large,,,,,not particularly electronegative,,,,,,thus the electrons are loosely held,,,,,this translates into allowing it to share with another atom..and attacking an electrophile .........a vacant orbital is a great place to put these electrons !
Hope this helps
Dr. Romano
