text: The intensity of the trans effect (as measured by the increase in rate of substitution of the trans ligand) follows this sequence:
  :F, HO, OH    , SCN, NO, SC(NH), Ph  , AsR, SR, CH , NO, CO, CN, CH
  The classic example of the trans effect is the synthesis of cisplatin and its trans isomer. Starting from PtCl, the first NH ligand is added to any of the four equivalent positions at random. However, since Cl has a greater trans effect than NH, the second NH is added trans to a Cl and therefore cis to the first NH.
  If, on the other hand, one starts from Pt(NH), the trans product is obtained instead:
  The trans effect in square complexes can be explained in terms of an addition/elimination mechanism that goes through a trigonal bipyramidal intermediate. Ligands with a high trans effect are in general those with high π acidity (as in the case of phosphines) or low-ligand lone-pair–d repulsions (as in the case of hydride), which prefer the more π-basic equatorial sites in the intermediate. The second equatorial position is occupied by the incoming ligand; due to the principle of microscopic reversibility, the departing ligand must also leave from an equatorial position. The third and final equatorial site is occupied by the trans ligand, so the net result is that the kinetically favored product is the one in which the ligand trans to the one with the largest trans effect is eliminated.