THE NATURE OF ROTATIONAL BARRIERS OF THE C-N BOND IN THIOAMIDES AND THE ORIGIN OF THE NONPLANARITY FOR THIOUREA

Citation
W. Kim et al., THE NATURE OF ROTATIONAL BARRIERS OF THE C-N BOND IN THIOAMIDES AND THE ORIGIN OF THE NONPLANARITY FOR THIOUREA, Journal of the Chemical Society. Faraday transactions (Print), 94(18), 1998, pp. 2663-2668
Citations number
34
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry Physical","Physics, Atomic, Molecular & Chemical
ISSN journal
0956-5000
Volume
94
Issue
18
Year of publication
1998
Pages
2663 - 2668
Database
ISI
SICI code
0956-5000(1998)94:18<2663:TNORBO>2.0.ZU;2-6
Abstract
The most important donor/acceptor interactions about the C(O)-N bond r otation in formamide are the barrier-forming N(1p)/C-O(pi) interactio n and the antibarrier-forming N(1p)/C-O(sigma) interaction. There is a large difference between the rotational barriers of formamide and ur ea. The most significant causes which lead to the low rotational barri er of urea are the reduction of the barrier-forming N(1p)/C-O(pi) int eraction energy and the existence of the antibarrier-forming N'(1p)/C- O(pi) interaction. The nonplanarity of the ground state for urea is c aused by the competition of the two former interactions. They come int o conflict with each other to a greater extent in the planar structure than in the nonplanar structure and this excessive conflict results i n the instability of the planar structure. To relax this strain, the g eometry is transformed into a stable nonplanar one. We found that the same interpretation as for formamide is applied to the thioamide syste m. The amide pi-orbital system was investigated to understand the chan ge in the C-N and C-O(S) bond length during the rotation process.