کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
9770228 | 1501942 | 2005 | 8 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Internal rotations of aromatic polyamides: a density functional theory study
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
شیمی
شیمی آلی
پیش نمایش صفحه اول مقاله
چکیده انگلیسی
Internal rotations of benzanilide (BA) and 4-(4â²-aminobenzamido)benzoic acid (AA) were investigated by density functional theory (DFT) calculations. B3LYP/6-31G* optimization for both BA and AA structures gives non-planar trans structures as the most stable conformers with lower energy of 4.60 and 5.08Â kcal/mol than cis ones, respectively. The amide bond and aniline moiety are found to be coplanar in transBA, while in trans phenyl benzoate (PB) the ester bond and benzoyl moiety are coplanar. The relaxed potential energy surface (PES) scans were then carried out with rotations of three single bonds, i.e. amide bond and both adjacent bonds. The discontinuous point is found on the relaxed PES for the amide bond rotation. This indicates that inversion of a pyramidal amino group is involved with the amide bond rotation. Therefore, two transition states (TSs) arise for rotation around the amide bond. Two TS structures (TS-1 and TS-2) were optimized for both BA and AA, and their activation energies were estimated as 14.34Â kcal/mol (TS-1) and 16.27Â kcal/mol (TS-2) for BA, and 12.20Â kcal/mol (TS-1) for AA, respectively. The TS-2 structure for AA failed to be optimized. The activation energy for the amide bond rotation, which is larger than that of 7.90Â kcal/mol for PB, as well as the coplanarity in aromatic amide is ascribed to the partial double bond character of amide bond. This is also confirmed by the Wiberg bond index (bond order). The chain persistence length for poly(4-benzamide) was estimated by the rotation matrix formalism using the calculated structural parameters of transAA. The estimated value of 1131Â Ã
is longer than our previously calculated value of corresponding aromatic polyester, 364Â Ã
for poly(p-hydroxybenzoic acid) [T. Imase, S. Kawauchi, J. Watanabe, Macromol. Theory Simul. 10 (2001) 434].
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Molecular Structure - Volume 741, Issues 1â3, 2 May 2005, Pages 221-228
Journal: Journal of Molecular Structure - Volume 741, Issues 1â3, 2 May 2005, Pages 221-228
نویسندگان
Joe Nishikawa, Tatsuya Imase, Masao Koike, Kaoru Fukuda, Masatoshi Tokita, Junji Watanabe, Susumu Kawauchi,