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Journal of the Korean Chemical Society (JKCS)

ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 50, Number 4
JKCSEZ 50(4)
August 20, 2006 

 
Title
Ab initio and DFT Study for the Internal Rotations of Cyclopropyldifluoroborane Molecule

Cyclopropyldifluoroborane 분자의 내부회전에 대한 이론적인 연구
Author
Chung-Kyung Lee, Kyeong-Yee Kim*

이정경, 김경이*
Keywords
시클로프로필, 하이퍼콘쥬게이션, 회전장벽, 밀도범함수이론, 순이론적계산방법 , Cyclopropyl, Hyperconjugation, Rotational Barrier, DFT, Ab initio
Abstract
Cyclopropyl 링과 할로겐 원소가 결합된 붕소원자 사이의 hyperconjugation 효과를 알아보기 위하여 CPDFB와 CPCFB 분자의 여러 conformation과 transition state 구조들에 대해 DFT와 ab initio 방법을 사용하여 다양한 레벨에서 구조최적화 및 NBO 분석을 수행하였다. 그 결과 주요 상호작용 형태는 화합물에 따라 단일결합 오비탈 σ(C1-C3, C2-C3) → n* (B9) 또는 σ*(B9-Cl11) 오비탈로 전자를 제공하는 것이었고 이때 안정화 에너지는 CPDFB 분자의 경우 6.63 kcal/mol, CPCFB 분자의 경우는 conformation에 따라 6.97(E-form)/6.79(Zform) kcal/mol 이었다. 또한, BF2와 BFCl 기의 내부회전에 의한 회전장벽의 크기는 각각 5.3~6.7 kcal/mol과 5.7~6.5 kcal/mol로 기존에 보고된 실험값과 잘 일치함을 보였다. 마지막으로 CPCFB 분자의 conformers 중에서 Z-form이 global minimum으로 확인되었고 E-form 보다 0.2 kcal/mol 정도 안정하였다.

The equilibrium structures, relative energies and NBO analyses for the possible conformations and transition states which can exist on the internal rotation of CPDFB and CPCFB molecules have been investigated using DFT and ab initio methods with various basis sets. The interaction between bonding orbital (σ(C1-C3, C2-C3)) and antibonding orbital (n*(B9) and σ*(B9-Cl11)) was the main characteristic hyperconjugation in both molecules. In addition, the stabilization energy of CPDFB was 6.63 kcal/mol and that of CPCFB was 6.97(E-form)/6.79(Z-form) kcal/mol for each conformation. The rotational barriers by internal rotation of BF2- and BFCl- functional groups were evaluated to be 5.3~6.7 kcal/mol and 5.7~6.5 kcal/mol respectively, which showed good agreement with the experimental values reported by previous dynamic NMR study. Finally, Z-form was more stable than E-form by 0.2 kcal/mol in CPCFB molecule and therefore Z-form was confirmed as global minimum.

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