The unusual ESR spectra of YBa2Cu3O7−x is ascribed to a Cu2+ ion, whose one ligand in CuO2 plane is involved in a peroxiton O−−Cu+−O− bond. The analysis shows that the presence of a ligand in O− substantially increases the energies ofd-hole orbitals. Since this increase for YBa2Cu3O7\t-\gd, orbital is much larger than that ford3z2−r2 orbital, their separation is drastically reduced and there occurs a significant orthorhombic mixing between the two. This charge transfer from a planardx2−r2 orbital to ad3z2−r2 orbital, which lies mainly perpendicular to the plane, provides a mechanism for interlayer coupling. The effect of this coupling on superconducting transition temperature is discussed.