Nucleophilicity

[RCT PC CRN]

Which is better nucleophile? CH3SH or CH3OH?

This is what I have got after an hour struggling with nucleophilicity. I still need your comments for above question.
There is no straight answer. It depends on solvent lot.
In polar protic solvent CH3SH is better nucleophile cause of the size of S.
In polar aprotic solvent CH3OH is better nucleophile cause O is more basic then S.

So my question, what would you do if Q doesn't specified solvent and simply ask which is better nucleophile? (IMO, you go with basicity and pick CH3OH as the best answer) Can I expect similar kind of ambiguity in Q during real DAT?

Will it make any difference if it is CH3SH and C2H5OH instead of CH3OH?

BTW, Destroyer sucks. 👎 There are many questions which are very ambiguous and explanations in the answer are bullcrap. Explanation to above is like.."S is larger than O, less electronegative than O, thus is more polarized. This means that the electrons are more loosely held; therefore, it would be the better nucleophile" Now how in the world S-H bond is more polarized then O-H bond since it clearly say S is less electronegative !!! S is bigger but it matters only in polar protic solvent and here in question they don't mention anything about solvent. Just freaking wasted so much of my time.

You can at least expect some kind of STANDARD when you pay some ridiculous amount of money.

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[UndergradGuy7]

If you use say CH3OH and nothing else then it is your solvent and it is protic (solvolysis). CH3OH = methanol = liquid.

How about an example from destroyer. I don't remember being confused abotu any questions from there with this.

 

[orgohacks]

Which is better nucleophile? CH3SH or CH3OH?

This is what I have got after an hour struggling with nucleophilicity. I still need your comments for above question.
There is no straight answer. It depends on solvent lot.
In polar protic solvent CH3SH is better nucleophile cause of the size of S.
In polar aprotic solvent CH3OH is better nucleophile cause O is more basic then S.

So my question, what would you do if Q doesn't specified solvent and simply ask which is better nucleophile? (IMO, you go with basicity and pick CH3OH as the best answer) Can I expect similar kind of ambiguity in Q during real DAT?

Will it make any difference if it is CH3SH and C2H5OH instead of CH3OH?

BTW, Destroyer sucks. 👎 There are many questions which are very ambiguous and explanations in the answer are bullcrap. Explanation to above is like.."S is larger than O, less electronegative than O, thus is more polarized. This means that the electrons are more loosely held; therefore, it would be the better nucleophile" Now how in the world S-H bond is more polarized then O-H bond since it clearly say S is less electronegative !!! S is bigger but it matters only in polar protic solvent and here in question they don't mention anything about solvent. Just freaking wasted so much of my time.

You can at least expect some kind of STANDARD when you pay some ridiculous amount of money.

It's a general problem with OChem by the way.

CH3SH is a better nucleophile than CH3OH.

Nucleophilicity is one of the most frustrating topics to learn, since it is dependent on so many factors like solvent, structure, and the type of reaction itself.

The tools to understand why sulfur is a good nucleophile aren't really given to you in undergrad Org 1 and Org 2. The reason is roughly that the electrons around S are less tightly held than they are around O, so they are better able to donate.

next time you are banging your head for an hour, send me a PM.

James

 

[jirotrom]

Indeed... James You are such a great help and If you don't mind I will be sending you multiple pms in the next 2 weeks 😀

 

[Ibraiz]

So to sum it all together
CH30H is a better nucleophile only in polar aprotic
CH3SH is a better nucleophile only in polar protic

?????????

What if the question does not mention anything about the solvent being polar protic or aprotic?

 

[rmm30]

Which is better nucleophile? CH3SH or CH3OH?

This is what I have got after an hour struggling with nucleophilicity. I still need your comments for above question.
There is no straight answer. It depends on solvent lot.
In polar protic solvent CH3SH is better nucleophile cause of the size of S.
In polar aprotic solvent CH3OH is better nucleophile cause O is more basic then S.

So my question, what would you do if Q doesn't specified solvent and simply ask which is better nucleophile? (IMO, you go with basicity and pick CH3OH as the best answer) Can I expect similar kind of ambiguity in Q during real DAT?

Will it make any difference if it is CH3SH and C2H5OH instead of CH3OH?

BTW, Destroyer sucks. 👎 There are many questions which are very ambiguous and explanations in the answer are bullcrap. Explanation to above is like.."S is larger than O, less electronegative than O, thus is more polarized. This means that the electrons are more loosely held; therefore, it would be the better nucleophile" Now how in the world S-H bond is more polarized then O-H bond since it clearly say S is less electronegative !!! S is bigger but it matters only in polar protic solvent and here in question they don't mention anything about solvent. Just freaking wasted so much of my time.

You can at least expect some kind of STANDARD when you pay some ridiculous amount of money.

While there is a lot of grey area in this subject there are some basic trends to rank nucleophile strength.

1: nucleophile strength increases with charge. Ex: OH- is a better nucleophile than H20. This is intuitive seeing as how OH- will donate electrons to an electrophilic carbon more readily.

2: nucphile strength increases across a row of periodic table from right to left. Ex: NH3 > H20. Across a row nucleophilicity increases with base strength. if there is a negative charge on the nucleophilic atom rule 1 takes priority over rule 2. Ex: OH- > NH3

From these two rules you would assume that nucleophile strength increases with base strength but that is NOT necessarily true. Nucphile strength only increases w/ base strength across a row.

3: nucphile strength increases going down a column: Ex: I- > F-. Here a weak base is (I-) is a strong nucph while F- is a poor nucleophile. In this way nucleophile strength increases with decreasing base strength down a column. Ex 2 CH3OS > CH3OH.

The reason nucph strength increases down a group is because the size of the nucleophile increases along this trend. This means 2 things:

1: The larger atom the less hindered it is by solvation in a polar protic solvent. A small atom like F- is covered "solvated" by solvent molecules that H bond to the F-, in a sense, blocking it from attacking the electrophilic C. A larger atom (I-) has greater area so it is not as hindered by H bonded solvent. This is why SN2 rxns are carried out thousands of times faster in aprotic solvents (eg DMF) than protic (H20).

2: As the atom increases in size so do the orbitals of that atom. Having large orbitals means that the overlap is greater when attacking the electrophile and that the electrons are further away from the nucleus (hence less tightly held) leading to a faster rxn

This is what is referred to as POLARIZABILITY and it describes an orbitals' tendency to become more diffuse and distorted as size of the nucleophile increases. I think you were mixing this concept up with polar bond which has to do with electronegativity difference. These are 2 DIFFERENT, but related ideas.



Some common pitfalls
Nucleophile strength ALWAYS increases with bascity
Polarizability and Polarization are the same thing


In addition im pretty sure that CH3SH is always a better nucleophile as long as they are in the same solvent.