Theoretical study of the structure and conformational behavior of some cyclopropane derivatives in the ground and excited electronic statesтезисы доклада
Аннотация:Structure and conformational dynamics of cyclopropanecarboxaldehyde (CpCHO), cyclopropanecarboxylic acid fluoride (CpCFO), and cyclopropanecarboxylic acid chloride (CpCClO) molecules were investigated in the ground (S0) and lowest triplet (T1) and singlet (S1) electronic states by various ab initio quantum chemistry methods (MP2 and CASPT2 in cc-pVTZ basis set).Calculations of equilibrium geometric parameters indicate that all considered molecules in S0 state are represented by cis- and trans-conformers with Cs symmetry. Our calculations of the structure of these molecules in the S1 and T1 states predicted the significant conformational changes being in result of electronic excitation: the rotation of cyclopropyl group and the pyramidalization of the carbonyl fragment (CCХO, X=H, F, Cl) that is planar in the S0 state.For modeling low-frequency vibrations one-dimensional (1D) and two-dimensional (2D) potential energy surfaces sections of molecules along the coordinates of low-lying vibration modes were constructed. Obtained vibrational energy levels in harmonic, 1D and 2D anharmonic models are compared. In studying the shapes of the potential energy surfaces (PES) of molecules, special attention is paid to the properties of the sections along the non-rigid vibrational coordinate corresponding to internal rotation. The constructed sections were used for solving a series of anharmonic quantum-mechanical vibrational problems. Analysis of the shape of the PES sections in the ground electronic state shows that the internal rotation is well separated from other molecular vibrations.However, analysis of the kinetic part of the Schrödinger equation shows that the internal rotation may be related to the low-frequency deformational vibration of the substituent (CHO, CFO and CClO). This relationship can be judged from an analysis of the change in kinematic factors Bij in the two-dimensional problem that takes into account these two studied nuclear motions. This dependence appears differently in the cis (φtors = 0°) and trans (φtors = 180°) conformers.
