What Factors Affect the Neucleophilicity and Basicity Order of I- Br- Cl- F-?

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In summary: So, in summary, the nucleophilicity and basicity order of I- Br- Cl- F- depends on various factors such as the size of the atom, polarizability, and solvation effects. However, there is no clear pattern and these concepts should be taken with a grain of salt as they are not always reliable. It is important to consider the specific conditions and environment when predicting nucleophilicity and basicity.
  • #1
cupid.callin
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I always have been confused about neucleophilicity and Basicity order of I- Br- Cl- F-

whenever i think of this ... 2 things come in my mind:

1. As F has smallest size so it will hold e- pair strolgly and thus will provide a very strong center for attack by some + charge ... so it must be a strong base
At same time (i read somewhere that Neucleophilicity depends on polarisibility i.e. how much an ion can deform to form bond ... please correct me if I'm wrong) it must be a bad Neucleophile ue to less polarisibility.
now I is big this e- pair is delocalized and thus will be a werk weak - spot for attack. now due to large polarisibility it must be a good Neucleophilicity.

2. As F is small so it will hold the e_ pair strongly and thus will not allow it to be shared by atoms easily. thus it must be a weak base

I read a page on wiki and understood this concept clearly but forgot what i understood over time :-p
i tried ... a lot ... i can't find that page again ...

please help me
also please tell me on what things Neucleophilicity and Basicity depends ...

Thanks !
 
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You are fishing in deep water indeed! You have probably hit on one of the areas where textbooks are least trustworthy. I summary, there are no such things as hard and soft acids, bases ornucleophiles. But, if you assume there are, you often end up with the correct answer and that's why the myth lives on.
In a vaccum, F- is the strongest nucleophile in the series, like you would expect. Poarizability has nothing to do with this. However, in a polar solvent F- is most strongly solvated, screened from interaction and therefore the weakest nucleophile.
The acidity/basicity order is as expected apart from HF being much weaker than expected. But, it isn't really, it just looks like it. Free HF is just a bit weaker than hydrochloric acid but most of the HF in aqueous solution is strongly hydrogen bonded to water or even forms something like HO...HFH. This masks the strenght of HF and makes it in effect a very weak acid.
 

FAQ: What Factors Affect the Neucleophilicity and Basicity Order of I- Br- Cl- F-?

1. What is the difference between nucleophilicity and basicity?

Nucleophilicity refers to the ability of a molecule or ion to donate a pair of electrons and form a new bond, while basicity refers to the ability of a molecule or ion to accept a proton. In other words, nucleophilicity is a measure of how reactive a species is towards electrophiles, while basicity is a measure of how reactive a species is towards acids.

2. How are nucleophilicity and basicity related?

Nucleophilicity and basicity are related in that both are influenced by the same factors, such as the electronegativity of the atom or functional group, the size of the atom or ion, and the presence of any electron-withdrawing or electron-donating groups. Generally, a species that is highly nucleophilic will also be highly basic.

3. How can we determine the nucleophilicity and basicity of a species?

The nucleophilicity and basicity of a species can be determined through experimental measurements, such as nucleophilic substitution or acid-base reactions, or through theoretical calculations using computational methods. Additionally, there are various scales and tables that rank the nucleophilicity and basicity of different species based on their chemical properties.

4. Why is understanding nucleophilicity and basicity important in organic synthesis?

Understanding nucleophilicity and basicity is important in organic synthesis because these properties play a crucial role in determining the outcome of reactions. For example, a highly nucleophilic or basic species may react more readily with an electrophilic or acidic substrate, leading to the formation of desired products. Additionally, controlling the nucleophilicity and basicity of reagents can help to achieve specific reaction pathways and increase reaction yields.

5. How can nucleophilicity and basicity be modified or controlled?

Nucleophilicity and basicity can be modified or controlled through several methods, such as the use of different solvents, changing reaction conditions (e.g. temperature, pH), or using different reagents or catalysts. Additionally, the addition of electron-withdrawing or electron-donating groups to a molecule can also impact its nucleophilicity and basicity, as these groups can either stabilize or destabilize the electron density and affect the reactivity of the molecule.

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