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Journal of the Korean Chemical Society (JKCS)

ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 30, Number 1
JKCSEZ 30(1)
February 20, 1986 

 
Title
Theoretical Studies on Orbital Interactions and Conformation of α-Substituted Acetones

α-치환 아세톤의 궤도간 상호작용과 형태에 관한 이론적 연구
Author
Ikchoon Lee, Kiyull Yang, Wang Ki Kim, Byung Hoo Kong

이익춘, 양기열, 김왕기, 공병후, 이병춘
Keywords
Abstract
α-치환아세톤(CH2XCOCH3, X = F, Cl, OH, SH 및 NH2)의 상대적 형태안정성을 결정하기 위하여 MNDO 및 STO-3G계산을 수행하였다. 계산결과 cis형이 더 안정한 F 및 NH2 치환 아세톤의 경우를 제외하고 모두 gauche형에 해당하는 형태이성체가 안정함을 밝혔다. gauche형에 대한 안정성은 σcx와 π*co궤도간의 two-orbital-two-electron상호작용에 의한 것으로 생각되며 이것은 gauche형에서의 vicinal overlap이 상당히 크다는 점과 두 궤도간의 hyperconjugation상호작용 때문에 π*co궤도가 낮아졌기 때문이다. 또한 gauche형에서의 여러가지 σ-π상호작용들은 X가 Cl 및 SH인 3주기 원자들에게 더 강함을 보였다. 한편 질소원자의 비결합궤도함수 nN과 인접 C-C σ결합의 상호작용은 cis일 경우 보다 trans배향일 경우에 더 강하였다.

MNDO and STO-3G calculations were performed to determine relative stabilities of rotamers for α-substituted acetones, CH2XCOCH3, X = F, Cl, OH, SH, and NH2. It was found that rotamers corresponding to gauche forms are preferred for all the α-substituents except for X = F and NH2, for which the cis forms were the preferred ones. The stability of gauche form was dictated by the stabilizing two-orbital-two-electron interaction σcx-π*co, operating uniquely in the gauche form due to the substantial vicinal overlap and energy gap narrowing between σcx and π*co orbitals. The energy gap narrowing was caused by the lowering of π*co level due to the hyperconjugative σ*cx-π*co interactions; the red shift in the n-π* transition was another effect of the relatively large σ*cx-π*co splitting. Various σ-π interactions in the gauche form were found to be stronger in the third-row hetero atom system, X = Cl and SH. Interactions between nonbonding orbital on N, nN and vicinal C-C σ bond were shown to be stronger in the trans than in the cis orientation.

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