Abstract
Critical assessment of performance of alternative molecular modeling methods depending on a specific object and goal of the investigation is a question of continuous interest. This prompted us to demonstrate the origin of the guidelines we have used for a rational choice and use of a proper low level calculation method (LLM) for an initial geometry optimization of generated conformers, with the aim of selecting a set for further optimization. What was performed herein was a comparison of LLMs: MM3, MM+, UFF, Dreiding, AM1, PM3, and PM6 on the optimization of conformers’ geometry of α-methoxyphenylacetic acid (MPA) 2-butyl esters as a set of typical diastereomeric esters of a chiral derivatizing agent. This set of esters calculated represents only compounds of this certain type in the current work. The LLM conformer energies were correlated with benchmark energies found by using higher level reference method B3LYP/6-311++G** on the geometries gained previously by optimization with LLMs. In an alternative treatment, the energy range to be covered and corresponding number of LLM optimized conformers obligatory for submitting to further optimization using a high level optimization cascade were considered on the basis of determination of the cut-off conformer (COFC).
Highlights
Critical assessment of performance of different alternative molecular modeling methods depending on the particular objects and specific goals is a question of continuous interest [1,2,3,4,5,6,7]
This prompted us to demonstrate the origin of the guidelines we have used for a rational choice and use of a proper low level calculation method (LLM) for an initial geometry optimization of generated conformers, with the aim of selecting a set for further optimization
The aim of the current work is to demonstrate how the guidelines are derived for a rational choice of a proper low level calculation method (LLM) for the initial geometry optimization of generated conformers in the total conformational analysis of diastereomeric esters
Summary
Critical assessment of performance of different alternative molecular modeling methods depending on the particular objects and specific goals is a question of continuous interest [1,2,3,4,5,6,7]. The aim of the current work is to demonstrate how the guidelines are derived for a rational choice of a proper low level calculation method (LLM) for the initial geometry optimization of generated conformers in the total conformational analysis of diastereomeric esters. The LLM chosen should allow selecting of a reliable set of conformers for further higher level optimization Having previously followed such guidelines in the total conformational analysis of several esters with up to 11 dihedrals in their structure, the initial optimization of thousands of conformers all together have afforded reliable sets of conformers. The following higher level optimization of the selected conformers has led to the results that, in turn, have allowed calculation of the molecular shielding models in exceptional accordance with differential shielding effects in the NMR spectra [8]. The most frequently used approach is to study the conformers’ geometry and relative energy as well as their barriers to the rotational interconversion
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