Inductive power?

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1 Answer
Aug 11, 2017

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"#