TAILIEUCHUNG - Thermodynamics Kinetics of Dynamic Systems Part 3

Tham khảo tài liệu 'thermodynamics kinetics of dynamic systems part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | First Principles of Prediction of Thermodynamic Properties 49 Pawar and collaborators Pawar et al. 1998 for cyclodecane based on the analysis of dynamic NMR spectroscopy carried out at K and theoretical calculations using ab initio level of theory. Cyclodecane has also been studied in the gas phase at K by means of a combination of electron diffraction and MM calculations Hilderbrandt Wieser Montgomery 1973 . In this case least square analysis of the experimental radial distribution curve utilizing the theoretical predictions for the four lowest-energy conformations indicated a more complex equilibrium composition BCB 49 3 TBC 35 3 TBCC 8 4 and BCC 8 4 . In the present Section we discuss an accurate analysis of the thermodynamic properties and conformational populations in order to assess the influence of the low frequency vibrational modes on the calculation of thermodynamic quantities as a function of temperature for the cyclodecane molecule. Among all possible conformers 15 true minima were located on the PES named S1 S2 . . . S15 with the boat-chair-boat BCB S1 being the lowest energy structure and characterized through harmonic frequency analysis. In Table 12 relative energies are shown for all conformers obtained from HF B3LYP and MP2 levels of theory. As can be seen from Table 12 the conformations S1 S2 S3 S4 and S5 also called BCB TBCC TBC BCC and TCCC respectively were found as the more stable forms with relative energies within 3 kcal mol-1. Based on these results we can assume that only these five conformations are present in the equilibrium in significant amounts. The structures of the main conformers are depicted in Figure 14. AEẹle-nuc HF 6-31G d p B3LYP 6-31G d p MP2 6-31G d p S1 BCB S2 TBCC S3 TBC S4 BCC S5 tCCC S6 S7 S8 S9 S10 S11 S12 S13 S14

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