Which is more nucleophilic

In all of them, the negative ends of the dipoles point away from the molecule. It is easy for them to solvate cations. The positive ends of the dipoles are closer to the middle of the molecule. It is difficult for them to get close to the anions. The result is that the nucleophile has few molecules in its solvent shell.

The nucleophile can more easily attack the substrate. Base Strength. C alkylation can be achieved. I understand that the presence of electron donating groups eg. Great question. These types of tradeoffs are what can make organic chemistry difficult. How do we decide that from anisole, nitrobenzene and benzene, what will be the correct order of rate of electrophillic substitution?

And can you possibly link me to an article related to it? You are soon gonna get a lot of Indian visitors. In OCH3 oxygen has got a lone pair due to which can be shared with the benzene ring through resonance hence increasing its charge density whereas nitrogen in NO2 has not got lone pair due to formation of dative bond with O and has higher electronegativity than C so it withdraws charge from benzene ring.

Hope it helps! Hello, Is it accurate to say that primary amines are more strongly nucleophilic than carboxylic acids? Many thanks for your help and time. Which one is it? It seems to me that you are contradicting yourself and making me more confused than I was previous to visiting this page…. Maybe I should have made this clearer. Also, that rule only applies for polar protic solvents. F - tends to H-bond with the solvent more, making it less reactive as a nucleophile, as compared to a nucleophile containing carbon.

The reverse of the rule is what actually applies in polar aprotic solvents. Since the solvent does not H-bond to the halide nucleophiles, fluorine basically becomes the most reactive among the halides. It took me way too long before I finally understood this whole nucleophile thing, but I hope my answer helped. Pyridine or Morpholine? Anyway, I think the answer is morpholine but I do not know how to explain it.

Could anyone please help me on this? I expect that, in pyridine nitrogen atom surrounded by three bons all of them with carbon atoms while in morpholine there are three bonds two of them with crbon and the thired one with hydrogen which is lower electronegative than carbon so the availability of unshered electron pair in morpholine more than that in pyridine. I mean which polar aprotic solvent may retard reaction?

That drives the equilibrium forward. Not quite. But steric hindrance due to the fact that a sigma star orbital is being attacked on carbon, versus an S orbital on hydrogen is the key difference. My question is why flouride ion behaves as a strong nucleophile in aprotic polar solvent when nucleophilisity is related to polarizability. Then why not iodide is a strong nucleophile in aprotic polar solvent and also iodide is less electronegative than fluoride so it should easily donate its lone pair of elctron.

It does not prefer to accommodate any other atom with it. Therefore fluoride is a better nucleophile than iodide. It says in my textbook that in methanol, RS- is a better nucleophile than iodide. I mean, sulfur is smaller and the R group is probably making it more basic by electron-donating effect, thus making it a stronger base. This means that RS- should be the most solvated one and therefore less nucleophilic. But according to Ms.

Paula Bruice, no, RS- is the better one. So, RS- would still have the stronger base, that would still be more solvated. I used to like Ochem a lot, but now I think I will never undestand it and it bums me out. Another thing, in a SN2 reaction, ammonia is the nucleophile and it is asked which solvent will make the reaction faster: ether or ethanol.

I would say ethanol, because it would stabitize the transition state by solvation, right? But, no, according to my professor, ether would be the best one because it would not make hydrogen bonds to ammonia. Please, help. Hi Symara — there are many factors involved in nucleophilicity. Hydrogen bonding is most important for atoms O, N, and F because of the large difference in electronegativity between these atoms and H.

When you compare that to S electronegativity 2. So the above answer RS- beats I- and ether being a better solvent than ethanol probably makes the most sense. As an aside, when talking about different variables like basicity or polarizability it is much clearer if you are going across a row or up and down a column of the periodic table. Comparing both at once e. Cl- and H2N- really requires looking at experimental evidence. Being challenged, need reasons why H2O instead of Br- became nucleophiles.

Textbooks with huge price tags just presents drawings of kind of skeletons, H2O and arrows. Here I get it. Thank you James. Great article! But I still have a question. I understand now how one nucleophile can be stronger or weaker than another, but what would you consider to be absolutely strong?

Just because one nucleophile is stronger than another does not mean they both cannot be weak nucleophiles, I think. What are the cuttoff points for strong nucleophiles that would be able to partake in SN2 reactions? We can come up with a good general scale for acidity, which can be measured by equilibria. The rate of the reaction is a combination of orbital overlap and charge density and by changing conditions like solvent, reagent, etc we can also affect nucleophilicity.

In either case, it is important that the nucleophile be a good Lewis base, meaning it has electrons it wants to share. The following diagram is just a reminder of some of the nucleophiles that were presented in the section covering nucleophilic substitution. In looking at these two types of nucleophiles, you should notice that a reactive atom, such as oxygen, in a neutral species can also be a reactive atom in a negatively charged species.

It has been experimentally shown that a nucleophile containing a negatively charged reactive atom is better than a nucleophile containing a reactive atom that is neutral. The next diagram illustrates this concept. Notice that when oxygen is part of the hydroxide ion, it bears a negative charge, and when it is part of a water molecule, it is neutral. Similarly, when nitrogen is part of NH 2 , it bears a negative charge, and when it is part of NH 3 , it is neutral. To say that nucleophilicity follows basicity across a row means that, as basicity increases from right to left on the periodic table, nucleophilicity also increases.

As basicity decreases from left to right on the periodic table, nucleophilicity also decreases. When it comes to nucleophilicity, do not assign this same rule when making comparisons between the halogens located in a column. In this case of moving up and down a column, nucleophilicity does not always follow basicity. It depends on the type of solvent you are using. In the section Nucleophilic Substitution, we assigned a relationship to leaving groups containing C, N, O, and F, showing that the strength of the leaving group follows electronegativity.

This is based on the fact that the best leaving groups are those that are weak bases that do not want to share their electrons. The best nucleophiles however, are good bases that want to share their electrons with the electrophilic carbon. The relationship shown below, therefore, is the exact opposite of that shown for the strength of a leaving group.

In general chemistry, we classified solvents as being either polar or nonpolar. Polar solvents can be further subdivided into protic and and aprotic solvents. F- are surrounded by an entourage of solvent molecules. By contrast, the least basic nucleophiles e. I- get involved with less hydrogen bonding, and are less hindered — therefore more nucleophilic. Here it comes again! The bulkier the groups that are adjacent to a nucleophilic atom, the slower the reaction will be and hence the poorer the nucleophile.

What Makes A Good Nucleophile? HO- is a better nucleophile than H2O.