Rank the relative nucleophilicity of halide ions in methanol solution. Most nucleophilic least…

Question 1

Rank the relative nucleophilicity of halide ions in methanol solution. Most nucleophilic least nucleophilic Br^-, I^-, F^-, Cl^- How is methanol classified? A. a polar protic solvent B. a polar aprotic solvent Nucleophilicity & Effect of Solvent: A nucleophile is an electron-rich species which seeks positive or electron-deficient sites. It either has a lone pair of electrons or has a negative charge. It attacks the electron-deficient sites and donates its lone pair of electrons. The strength of a nucleophile is called its nucleophilicity. The nucleophilicity depends on various factors like the nature of the solvent, electronegativity of the element carrying the lone pair of electrons, etc.


Question 2


Question 3


Question 4


Answer to question 1

(1) Methanol is a polar protic solvent as it has a highly electronegative oxygen atom bonded to a hydrogen atom which can be released.

(2) Methanol being a polar protic solvent, forms hydrogen bonds or have stronger dipole-dipole forces with smaller halogen atoms.

This decreases their ability to donate their lone pairs and decreases their nucleophilicity.

Thus, the order of nucleophilicity is:


Answer to question 2

The order of nucleophilicity :

The order of nucleophilicity can be written by observing the below points,

  • Less is the electronegativity of element more is nucleophilicity.

                   So, as S is less electronegative than O and hence, CH3S– > CH3O

  • The negative charge increases the nucleophilicity,

So,

CH3O > CH3OH

CH3COO > CH3COOH

 And,  CH3COO > CH3O

So, the overall order of nucleophilicity is

CH3S– > CH3O– > CH3COO > CH3OH > CH3COOH


Answer to question 3

I->Br->Cl->F-

decreasing order of nucleophilicity

iodide ion>bromide ion>chloride ion >fluoride ion

because in the polar protic solvent the solvolysis of the fluoride ion will be most resulting in the least nuceophilicity 


Answer to question 4

1) Acetonitrile is a polar aprotic solvent because it is a very very weak acid (pKa around 30).The nucleophilicity will be

F- > cl- > br- > i- >

2) a polar aprotic solvent

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