Hi Alexandra!

I believe that there may have been a typo in the answers. Alcohols are not better nucleophiles than thiols. By and large, increased electronegativity (the ability to attract electrons) would suggest that an atom is better at holding onto its electrons, which is NOT the sign of a good nucleophile, as it wants to donate its electrons!

Furthermore, when comparing nucleophilicity between oxygen and sulfur, we should be considering the atomic size, not electronegativity.

In general for nucleophilicity, we need to consider the following:

1. Are the atoms acting as nucleophile the same? If so, then nucleophilicity parallels basicity.
2. Are the atoms you are comparing in the same row? If so, consider electronegativity. Decreased electronegativity means increased nucleophilicity (nucleophilicity increases towards the left).
3. Are the aotms you are comparing in the same group? If so, consider atomic size. Larger the atoms, easier it is to donate electrons (nucleophilicity increases down the group, generally; halogens are special and need consideration of its solvents).

Therefore, a sulfur atom would be considered a better nucleophile than oxygen due to its larger size.

I hope this helps! :)

Cheers,

Molly