Dissociation constants (pKa) of the protonated isomeric secondary aliphatic amines (I and II), containing CF 3-group at, α- or p-position, have been determined by potentiometric titration in H 2O and CH 3NO 2. CF 3CHBrCH 2NHR (I, a-c) CF 3CH(NHR)CH 2Br (II, a-c) RMe(a), Et(b), Bz(c). ▪ The appearance of CF 3-group at α-position of the amines leads to the sharp decreasing (4-5 orders) of their basicities as compared with the isomeric compounds containing β-CF 3-groups. Such influence one can naturally explain in terms of the lowering of electronic population on nitrogen atom under the strong inductive effect of CF 3-group. However surprisingly, the quantum-chemical AM1 calculations show that the total charges on nitrogenes in CF 3CHBrCH 2NH 2 (I, d) and CF 3CH(NH 2)CH 2Br (II, d) are equal (−0, 34). The real differences exist in the frontier orbitals energy levels (I, d −10, 30 and −0, 36 eV; II, d −10, 72 and +0, 15 eV), which determine the basicity magnitudes.