Question

How can I distinguish Cl- ion trans effect and easy leaving group?

Answer 1

Trans effect :

The effect of a ligand to substitute another ligand present on trans position to it in a square planar complexes is called as trans effect.

Trans influence is an thermodynamic factor in which some ligands having greater electronegativity weaken the M-L bond present trans to them in a complex and thus resulting in substitution at trans position.

e.g. H- ,I-, Cl-, etc.

Thus as Cl- ion has more electronegativity it weakens the M-L bond of ligand having less electronegativity and present on trans position to Cl- by attracting th pair of bond electrons towards it . Due to this substitution takes place easily.

Order of trans effect shown by ligands :

F⁻, H₂O, OH⁻ < NH₃ < py < Cl⁻ < Br⁻ < I⁻, SCN⁻, NO₂⁻, SC(NH₂)₂, Ph⁻ < SO₃²⁻ < PR₃, AsR₃, SR₂, CH₃⁻ < H⁻, NO, CO, CN⁻, C₂H₄

_{Leaving group ability :}

The ability of an atom or group to undergo substitution by another group more nucleophilic than former easily and thus increasing the rate of reaction is called leaving group ability.

Weak bases or poor electron donors are good leaving groups.

leaving group ability increases from left to right in a period due increase in electronegativity and it decreases down the group.

As chlorine is electronegative, it is a weak base and a good leaving group.