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木虫 (小有名气)

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金币: 1974
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虫号: 357956

[交流] 【求助】[10金币求教]发晶体学报C时，comment倒数第二段，氢的位置该怎么描述

在学校的分析测试中心做的晶体衍射，没有说明该怎么样描述氢的位置。看到有文献这样写, 但是不懂什么意思，请高手帮忙解释一下。All of H atoms were found in a different Fourier synthesis. In order to maximize the data/parameter ratio, H atoms bound to C atoms were placed in geometrically idealized positions (C—H = 0.93–0.98 Å and N-H = 0.86 Å AFIX 43) and constrained to ride on their parent atoms, with Uiso (H) values of 1.2Ueq(C, N). The OH groups were refined as rigid groups allowed to rotate but not tip (AFIX 147), with O—H distances of 0.82 Å and Uiso (H) values of 1.5Ueq(O).（这段话是不是通用的？Uiso (H) values of 1.2Ueq(C, N). Uiso (H) values of 1.5Ueq(O).分别是什么意思？AFIX 43和AFIX 147又是什么意思？）

还有人这样写的：
In the absence of suitable anomalous scattering, Friedel equivalents
could not be used to determine the absolute structure. Refinement
of the Flack (1983) parameter led to an inconclusive value
[0.4 (6)]. Therefore, 1693 Friedel equivalents were merged before the
final refinement and the known configuration of the parent molecule
was used to define the enantiomer of the final model. (这段是什么意思? 为什么有的文章写这一段，有的不写？这里面对应数字在哪个文件中可以找到)

All H atoms were found in a difference Fourier synthesis. The OH groups were
refined as rigid groups allowed to rotate but not to tilt, with O—H =
0.82 A ° and Uiso(H) = 1.5Ueq(O). The remaining H atoms were placed
in geometrically idealized positions, with C—H = 0.93–0.98 A ° and
N—H = 0.86 A ° , and constrained to ride on their parent atoms, with
Uiso(H) = 1.2Ueq(C,N)

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1楼 2011-01-24 20:21:06

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