| 查看: 707 | 回复: 3 | |||
| 当前主题已经存档。 | |||
| 当前只显示满足指定条件的回帖，点击这里查看本话题的所有回帖 | |||
[交流]
Flack parameter什么意思，怎么求出
|
|||
|
Flack parameter是关于什么的参数，怎么计算? 好像与手性有关??? |
回复此楼» 猜你喜欢
中南大学易小艺课题组诚招2026申请-考核制博士生
已经有0人回复
-
海南师范大学招收化学博士（光电功能材料课题组招收博士研究生）
已经有11人回复
-
无机化学论文润色/翻译怎么收费?
已经有97人回复
-
求助几个团簇的cif
已经有0人回复
-
急求该反应的详细机理
已经有5人回复
-
【Ei | Scopus 双检索】2026年智能交通与未来出行国际会议（CSTFM 2026）
已经有0人回复
-
【EI|Scopus 双检索】2026年第六届机器人与人工智能国际会议（JCRAI 2026）
已经有0人回复
-
zotero的advanced material模板没有更新，有人有新版的cls文件吗
已经有2人回复
-
【高校联合举办】2026年第五届服务机器人国际会议（ICoSR 2026）
已经有0人回复
3楼2009-08-09 21:55:08
xi2004
至尊木虫 (职业作家)
- CMEI: 10
- 应助: 125 (高中生)
- 金币: 16769.9
- 散金: 12393
- 红花: 221
- 帖子: 4161
- 在线: 436.9小时
- 虫号: 354550
- 注册: 2007-04-24
- 专业: 结构化学
★ ★ ★ ★ ★ ★ ★ ★ ★
xiaxinle(金币+1):谢谢参与
xiaxinle(金币+7,VIP+0):thanks 8-10 10:48
paopaomeng(金币+1,VIP+0):谢谢交流 8-26 09:34
xiaxinle(金币+1):谢谢参与
xiaxinle(金币+7,VIP+0):thanks 8-10 10:48
paopaomeng(金币+1,VIP+0):谢谢交流 8-26 09:34
|
就是所谓的绝对构型因子. 表征你的结构的绝对构型的. http://en.wikipedia.org/wiki/Flack_parameter Flack parameter From Wikipedia, the free encyclopedia Jump to: navigation, search This article is an orphan, as few or no other articles link to it. Please introduce links to this page from other articles related to it. (February 2009) In X-ray crystallography, the Flack parameter is a factor used to estimate the absolute configuration of a structural model determined by single-crystal structure analysis. In this approach, one determines the absolute structure of a noncentrosymmetric crystal. The processes used to decide the absolute structure use the anomalous dispersion effect. If atomic scattering factors did not have imaginary parts, the Friedel pairs would have exactly the same amplitudes (i.e., the scattering intensity | F(hkl) | 2 from crystal plane (h k l) is equal to | F( − h − k − l) | 2). However, atomic scattering factors have imaginary parts due to the anomalous dispersion effect, and Friedel's law is broken by this effect. There are several ways to determine the absolute structure by X-ray crystallography. For example, a comparison of the intensities of Bijvoet pairs or of the R factors for the two possible structures can suggest the correct absolute structure. One of the more powerful and simple approaches is using the Flack parameter, because this single parameter clearly indicates the absolute structure. The Flack parameter is calculated during the structural refinement using the equation given below: where x is the Flack parameter, I is the square of the scaled observed structure factor and F is the calculated structure factor. By determining x for all data, x is usually found to be between 0 and 1. If the value is near 0, with a small standard uncertainty, the absolute structure given by the structure refinement is likely correct, and if the value is near 1, then the inverted structure is likely correct. If the value is near 0.5, the crystal may be racemic or twinned. The technique is most effective when the crystal contains both lighter and heavier atoms. Light atoms usually show only a small anomalous dispersion effect. This parameter, introduced by H. D. Flack [1] became one of a standard set of values being checked for structures with noncentrosymmetric space groups. [edit] References ^ H. D. Flack (1983). "On Enantiomorph-Polarity Estimation". Acta Cryst A39: 876–881. |
2楼2009-08-09 21:46:18
