TheA1molecular vibrations of the bent symmetrical XY2model are considered. A generalized bending, Ω, is defined in such a way that the (i) ordinary (Decius') bending, (ii) Keating's bending, (iii) the nonbonded (Urey-Bradley-type) stretching and (iv) symmetrical bond stretching all become special cases of it. The force constant denotedF12(Ω) is of interest as a function of Ω. In the numerical example of H2O,F12(Ω)= 0 holds for Ω = 107.2°, which is not far from the interbond equilibrium angle, 2A= 104.53°. This is consistent withF12k≈ 0, where the force constant pertains to the Keating coordinates. In the same connection one finds the KFF (Keating force field) to be superior to the VFF (valence force field) as well as CFF (central force field). Some numerical results are also given for NO2, 03, SO2, ClO2, FlO2, Cl2O and Cl2S. In these cases no general conclusion can be drawn with regard to the superiority of the different coordinate types. As an appendix some explicit formulas are given for the mean amplitudes of vibration (ι) and perpendicular amplitude correction coefficients (K) of the considered molecular model. Numerical values of ι andKfor water are reported.