In this work we present an octahedral perturbative model to explain the dependence of the crystal-field (CF) and the charge-transfer (CT) energy with respect to structural distortions in Jahn-Teller (JT) ${\mathrm{CuCl}}_6^{4\mathrm{-}}$ systems. The method provides a simple way to express the variation of electronic energy to complex distortions of the totally symmetric mode $Q_{a_{1g}}$ and the JT mode $Q_{\theta },$ as a function of the corresponding electron-vibration coupling constants, $[\partial E/\partial Q_i{]}_{O_h}$ ${(i=Q}_{a_{1g}}$ and $Q_{\theta }).\mathrm{}$ A value of 9100 ${\mathrm{cm}}^{\mathrm{-}1}$/Å for the linear JT coupling constant $A_1$ has been obtained for the octahedral ${}^2{E}_g{(x}^2-y^2,{3z}^2-r^2)$ CF state $(e\otimes E)$ from structural correlations along a series of copper compounds. The corresponding JT coupling for the ${}^2{T}_{1u}\left(\pi \right)$ CT state $(e\otimes T),$ $A_2=3000\mathrm{}{\mathrm{cm}}^{\mathrm{-}1}/\AA ,$ has been derived from hydrostatic pressure measurements performed on the ${(\mathrm{C}}_3{\mathrm{H}}_7{\mathrm{NH}}_3{)}_2{\mathrm{CuCl}}_4$ perovskite layer. A noteworthy conclusion of this model is that a redshift of the intense $e_u\left(\pi \right)\to b_{1g}{(x}^2-y^2)$ CT band is possible in axially elongated ${\mathrm{CuCl}}_6^{4\mathrm{-}}$ systems upon anisotropic volume reduction, if the axial distance decreases more rapidly than the equatorial distance by $|\Delta R_{\mathrm{ax}}|>30\mathrm{}|\Delta R_{\mathrm{eq}}|.$ These results are discussed in light of recent pressure experiments carried out in wide-gap CT semiconductors of the $A_2{\mathrm{CuCl}}_4$ family.