Question

Inductive power?

Answer 1

The relative order of -I effects is `"CF"_3 > "CCl"_3 > "OH" > "OR"`

Explanation:

The -I effect is the decrease in electron density in one portion of a molecule caused by electron-withdrawing somewhere else in the molecule.

It is usually caused by an electronegatvity difference (`ΔEN`) between the atoms at either end of a bond.

For example, here are the electronegativity differences for three bonds:

`bb("Bond"color(white)(m)ΔEN)`
`color(white)(l)"C-F"color(white)(mml)1.43`
`color(white)(l)"C-Cl"color(white)(mm) 0.61`
`color(white)(l)"C-O"color(white)(mml) 0.89`

`ΔEN` is greatest for the `"C-F"` bond. so order of -I effects is `"CF"_3 > "CCl"_3`.

`ΔEN` is for the `"C-Cl"` bond is less than `ΔEN` for the `"C-O"` bond, but there are three `"C-Cl"` bonds.

Hence, I would expect the order to be

`"CF"_3 > "CCl"_3 > "C-O-"`

An alkyl (R) group is electron donating. so it would reduce the -I effect of the `"O"` atom.

Thus `"OH > OR"`

and the final order becomes

`"CF"_3 > "CCl"_3 > "OH" > "OR"`