Drastic influence of the intramolecular cat ion-ʌ interaction o n the basi city of selected amines: AIM a nd NBO analysis

In thi s study, drastic influen ce of the intramolecular cation-ʌ interaction on the basicity of select ed amines has been considered. The optimized minimum-energy geometries of different studied amines and their protonated structures were determined by using DF T calculati ons at the B۳LYP/۶-۳۱۱++G(d,p) l evel of theory. All gas phase computations were perform ed at level MP۲/۶-۳۱۱ ++G(d,p)//( B۳LYP/۶-۳۱+G(d). Sol vation was included in the calcul ations using the polariz ed continuum model (PCM). Structure optimi zation in solution phas e was performed using the structure s optimized in gas phase at the H F/۶-۳۱G(d,p) level of th eory. Geometry optimizations indicate that the most stable structures are stabilized by intram olecular cat ion-ʌ interaction. The proton affinity (PA) of selected amines is controlled by th e strength o f intramolecular cation -ʌ interaction of ammuniom with aromatic g roup. These cation-ʌ interactions strongly infl uence the b asicity of a mines. The highest PA value amon g the studi ed amines was found to be ۲۲۹.۳ kcal/mol for para methoxy benzene butan amine. This is compa rable with proton af finity of H MPA. The solution phase calculations were carried out in aqueous solution. N atural bond orbital (N BO) analysis was performed to calculate the charge transfe rs and the second-order interaction energies ( E (۲)) between the donor and acceptor. Quantum theory of atoms in m olecules (Q TAIM) wa s also applied to determ ine the nature of cation-ʌ interaction. QTAIM studies showed th at the intram olecular cation-ʌ interaction in these structures is electrostatic (closed-shell) intera ctions.

کلیدواژه ها:

Basicity ، Cation-ʌ interaction ، DFT ، N atural bonding orbital ( NBO) ، Qua ntum theory of atoms in molecules (QTAIM)