کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5418117 | 1506940 | 2008 | 5 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
How steric effects favor thiepins over their benzene sulfide tautomers at theoretical levels?
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
شیمی
شیمی تئوریک و عملی
پیش نمایش صفحه اول مقاله
چکیده انگلیسی
The change of enthalpies, energy differences, activation energies and equilibrium constants (at 298 K), for valence tautomerizations between 2,7-di(X)benzene sulfides (BX-X) and 2,7-di(X)thiepins (TX-X), also between 2-tert-butyl-7-(X)benzene sulfide (BX-Y) and 2-tert-butyl-7-(X)thiepin (TX-Y), are estimated at ab initio (MP2/6-311++Gââ, HF/6-311++Gââ) and DFT (B3LYP/6-311++Gââ) levels, where X = H, Me, Et, i-Pr, and Y = t-Bu. For X = H, benzene sulfide (BH-H) is more stable than thiepin (TH-H) (ÎH = 6.37 kcal molâ1), in the above BX-X/TX-X series. Likewise, BH-t-Bu is more stable than TH-t-Bu (ÎH = 5.62 kcal molâ1), in BX-Y/TX-Y series. In contrast, for X = Me, Et, and i-Pr, steric effects shift the equilibrium in favor of TX-Y in such a way that Keq for Bi-Pr-t-Bu/Ti-Pr-t-Bu is about 109 times greater than that for BH-t-Bu/TH-t-Bu. The B3LYP/6-311++Gââ calculated activation energies for inversions of thiepins to their mirror images, show higher energy barriers for all the TX-Y thiepins, compared to their corresponding TX-X analogues. Magnetic (NICS) criterion indicates virtual non-aromaticity for all TX-X and TX-Y thiepins, but extreme antiaromaticity for all their corresponding inversion transition states.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Molecular Structure: THEOCHEM - Volume 861, Issues 1â3, 30 July 2008, Pages 117-121
Journal: Journal of Molecular Structure: THEOCHEM - Volume 861, Issues 1â3, 30 July 2008, Pages 117-121
نویسندگان
M.Z. Kassaee, S.M. Musavi, M.R. Momeni, F.A. Shakib, M. Ghambarian,