Why is bromine a better nucleophile

Bottom line: as electronegativity increases, nucleophilicity decreases. Going down the periodic table, another factor comes into play next. In so doing, the nucleophile is considerably less reactive; everywhere it goes, its lone pairs of electrons are interacting with the electron-poor hydrogen atoms of the solvent. The ability of nucleophiles to participate in hydrogen bonding decreases as we go down the periodic table.

Hence fluoride is the strongest hydrogen bond acceptor, and iodide is the weakest. A polar aprotic solvent does not hydrogen bond to nucleophiles to a significant extent, meaning that the nucleophiles have greater freedom in solution. Under these conditions, nucleophilicity correlates well with basicity — and fluoride ion, being the most unstable of the halide ions, reacts fastest with electrophiles.

If we want a reaction to take place, we need to use solvents that will actually dissolve our nucleophile. The bottom line here is that the bulkier a given nucleophile is, the slower the rate of its reactions [and therefore the lower its nucleophilicity]. Note: Are there other factors? This list of four covers the basics, but several other factors are worth noting.

Iodide, being larger, will have a lower charge density and interactions with hydrogen will be weaker. Does that make sense to you? Its actually the opposite. Since flourine is smaller, its charge is confined to a smaller space and it therefore has a higher electron density. They are correlated most of the time but not always. How is polarizability related to nucleophilic strength? Would it fit into any of these categories? Polarizability plays a role when you take the solvent into account.

In polar protic solvents, hydrogen bonding occurs between the partial positive hydrogen H attached to N or O usually and the nucleophile.

Smaller nucleophiles become more solvated than larger nucleophiles, which means that smaller nucleophiles in polar protic solvents will not be able to react as well and thus are poorer nucleophiles. For example, Florine anions become so heavily solvated in polar protic solvents that they wont even react, but Iodine, being much larger, is much less solvated and can still react.

In aprotic solvents, hydrogen bonding does not occur to any significant extent and the stronger base is usually the stronger nucleophile. If this list does not take into account all the factors that make a good nucleophile, where is a more detailed treatment of the ones that are remaining? Also, in the case of polar aprotic solvents, one may mention the idea of the cation being solvated, while the anion nucleophile less so, and so it is more reactive. One example is the differing selectivity of enolates for C vs.

O alkylation; depending on the nature of the solvent, counter-ion, and electrophile, either dominant O vs. 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. If they bond to a hydrogen atom, we call them bases.

If they bond to any other atom especially carbon , we call them nucleophiles. A good base is usually a good nucleophile. So, strong bases — substances with negatively charged O, N, and C atoms — are strong nucleophiles. Beato Viade Professional. Why is fluorine a bad Nucleophile? Hydrogen Fluoride is not one of the strong acids.

It's a weak base The affinity it has for hydrogen is what makes it a poor nucleophile. It would rather grab a hydrogen and leave than attack an electrophilic site. Arlete Burca Explainer. Which is the strongest nucleophile? When we considered the effects of protic solvents, remember that the iodide anion was the strongest nucleophile. Now, in considering aprotic solvents under some conditions, the fluoride anion is the strongest nucelophile.

Mijail Vitry Explainer. What is a weak nucleophile? Weak nucleophiles are neutral and don't bear a charge. So let's look at the 4 examples I started with yesterday.

Example 1 uses NaCN a strong nucleophile. Codou Stefani Pundit. Is water a good Nucleophile? Because there isn't a full negative charge, water isn't going to be as good a nucleophile as a negative ion like OH - , and so the reaction is slower.

Reita Slany Pundit. Is I a strong or weak nucleophile? In general, good bases are also good nucleophiles. Therefore, strong bases such as negatively charged oxygens and nitrogens will also be strong nucleophiles. In terms of the halohydrin reaction, your friend is correct.

The water molecule will attack first because it is the solvent in the reaction, and with water being the solvent, that means there are many more molecules of water than there are bromide ion. If you think in terms of Avogadro's number, a mole of bromide ion contains 6. Therefore, a water molecule will more than likely attack first, leading to addition of water and a bromine atom. However, in terms of nucleophilicity, a bromide ion is probably a better nucleophile than a water molecule because the bromide ion has a negative charge, and negatively charged species tend to be better nucleophiles in organic chemistry.

Ask Question. Asked 6 years, 9 months ago. Active 3 years, 11 months ago. Viewed 5k times. The question is, was my professor wrong or is there something I'm missing? Thank you very much. Improve this question. Natim Natim 1 1 silver badge 3 3 bronze badges. Add a comment. Active Oldest Votes. Improve this answer. Jori Jori 5, 6 6 gold badges 29 29 silver badges 66 66 bronze badges. Will not water will be more extensively hydrogen bonded? However, the concentration effect is indeed overwhelming.