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题名: Study on conformation interconversion of 3-alkyl-4-acetyl-3,4-dihydro-2H-1,4-benzoxazines from dynamic NMR experiments and ab initio density functional calculations
作者: Yang, G;  Han, XW;  Zhang, WP;  Liu, XM;  Yang, PY;  Zhou, YG;  Bao, XH
刊名: JOURNAL OF PHYSICAL CHEMISTRY B
发表日期: 2005-10-06
DOI: 10.1021/jp050874d
卷: 109, 期:39, 页:18690-18698
收录类别: SCI
文章类型: Article
WOS标题词: Science & Technology ;  Physical Sciences
类目[WOS]: Chemistry, Physical
研究领域[WOS]: Chemistry
英文摘要: Variable-temperature NMR experiments and ab initio density functional calculations were carried out to investigate the conformation interconversion of novel chiral 3-alkyl-3,4-dihydro-2H-benzo[1,4]oxazine derivatives. With CDCl3 as the solvent, the coalescence temperatures of H-2, H-3, H-11 and H-19 of product 1 are about 289, 304, 292, and 316 K, with the corresponding activation free energies at 58.0 +/- 6.7, 60.9 +/- 7.1, 58.3 +/- 6.8, and 59.6 +/- 6.9 kJ(.)mol(-1), respectively. When dimethyl sulfoxide (DMSO-d(6)) was used as the solvent, H-1 and C-13 NMR signals were completely assigned at 375 K. The effects of solvent and temperature were investigated through a polarizable continuum model. At each theoretical level (MP2 or B3LYP), the changing tendencies of the calculated activation free energies and interconversion rates agree well with those of the NMR results. In addition, the interconversion rate at each specified temperature was calculated to be about 1.5 times faster in DMSO-d6 than in CDCl3. Accordingly, we failed to observe the coalescence phenomena of H-3 and H-19 in DMSO-d(6) by NMR measurements from 296 to 375 K. The substitution effect at the R-1-R-5 positions was considered using density functional calculations, with the activation barriers decreasing as follows: product 6 > 3 > 1 > 7 > 2. This sequence is consistent with that of the reaction heats, except for product 7, implying that the interconversion processes may be thermodynamically controlled. Surprisingly, the substituted groups near the acetyl group in product 2 and 7 do not elevate the activation barrier but, instead, lower it somewhat, with the possible reasons for this provided in the paper.
关键词[WOS]: POLARIZABLE CONTINUUM MODEL ;  MOLECULES ;  EXCHANGE
语种: 英语
WOS记录号: WOS:000232318500065
Citation statistics: 
内容类型: 期刊论文
URI标识: http://cas-ir.dicp.ac.cn/handle/321008/139930
Appears in Collections:中国科学院大连化学物理研究所_期刊论文

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作者单位: 1.Chinese Acad Sci, Dalian Inst Chem Phys, State Key Lab Catalysis, Dalian 116023, Peoples R China

Recommended Citation:
Yang, G,Han, XW,Zhang, WP,et al. Study on conformation interconversion of 3-alkyl-4-acetyl-3,4-dihydro-2H-1,4-benzoxazines from dynamic NMR experiments and ab initio density functional calculations[J]. JOURNAL OF PHYSICAL CHEMISTRY B,2005,109(39):18690-18698.
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