CoachThe trans effect is the acceleration of the substitution of a ligand by the ligand trans to it: a kinetic effect, on the transition state. The trans influence is the weakening, in the ground state, of the bond trans to a ligand, seen in bond lengths and vibrational frequencies: a thermodynamic effect.
![The trans effect at work (charges omitted). Top: from [PtCl4]2-, the second ammonia replaces a chloride trans to chloride (Cl- has the larger trans effect), giving the cis isomer, cisplatin. Bottom: from [Pt(NH3)4]2+, the second chloride replaces the ammonia trans to the first chloride, giving the trans isomer.](/images/onecourse/chapters/chemistry-4/b3-complex-mechanisms/fig-2ba289e8a7fc.svg)
![The trans effect at work (charges omitted). Top: from [PtCl4]2-, the second ammonia replaces a chloride trans to chloride (Cl- has the larger trans effect), giving the cis isomer, cisplatin. Bottom: from [Pt(NH3)4]2+, the second chloride replaces the ammonia trans to the first chloride, giving the trans isomer.](/images/onecourse/chapters/chemistry-4/b3-complex-mechanisms/fig-93314eebd310.svg)