Nucleophilicity trends are opposite electronegativity trends. Oxygen is more electronegative than sulfur and thus less nucleophilic. (Basically, oxygen wants it's electrons more and is less likely to share.)
Nucleophilicity trends are opposite electronegativity trends. Oxygen is more electronegative than sulfur and thus less nucleophilic. (Basically, oxygen wants it's electrons more and is less likely to share.)