Difference between revisions of "Flack parameter"
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| + | <font color="blue">Paramètre de Flack</font> (''Fr''). <font color="red">Flack-Parameter</font> (''Ge''). <font color="black">Parametro di Flack</font> (''It''). <font color="purple">フラック変数</font> (''Ja''). <font color="green">Parámetro de Flack</font> (''Sp''). | ||
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== Definition == | == Definition == | ||
| − | The Flack parameter is the molar fraction < | + | The Flack parameter is the molar fraction <math>x</math> in the defining equation <math>C=(1-x)X + x\bar X</math>, where <math>C</math> represents an oriented two-domain-structure crystal, [[twinning by inversion|twinned by inversion]], consisting of an oriented domain structure <math>X</math> and an oriented inverted domain structure <math>\bar X</math>. In reciprocal space, the Flack parameter <math>x</math> is defined by the structure-amplitude equation |
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| + | <math>G^2(h,k,l,x)=(1-x)|F(h,k,l)|^2 + x|F({\bar h}, {\bar k}, {\bar l})|^2</math>. | ||
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| + | For a multidomain-structure twin of a chiral crystal structure, an equivalent Flack parameter may be calculated according to the method of Flack and Bernardinelli (1999). | ||
| + | == See also == | ||
| + | *[[Absolute structure]] | ||
== Related chemical terms == | == Related chemical terms == | ||
| − | The [http://www.chem.qmul.ac.uk/iupac/stereo/ IUPAC ''Basic Terminology of Stereochemistry''] contains definitions of related chemical terms of use to the crystallographer, ''viz'': ''absolute configuration'', ''chiral'', ''chirality'', ''chirality sense'', ''enantiomer'', ''enantiomerically pure'', ''enantiomorph'', ''racemate'', ''racemic'', ''racemic conglomerate'' and ''relative configuration''. | + | The [http://www.chem.qmul.ac.uk/iupac/stereo/ IUPAC ''Basic Terminology of Stereochemistry''] contains definitions of related chemical terms of use to the crystallographer, ''viz'': [http://www.chem.qmul.ac.uk/iupac/stereo/A.html#01 ''absolute configuration''], [http://www.chem.qmul.ac.uk/iupac/stereo/BC.html#16 ''chiral''], [http://www.chem.qmul.ac.uk/iupac/stereo/BC.html#17 ''chirality''], [http://www.chem.qmul.ac.uk/iupac/stereo/BC.html#22 ''chirality sense''], [http://www.chem.qmul.ac.uk/iupac/stereo/DE.html#24 ''enantiomer''], [http://www.chem.qmul.ac.uk/iupac/stereo/DE.html#28 ''enantiomerically pure''], [http://www.chem.qmul.ac.uk/iupac/stereo/DE.html#32 ''enantiomorph''], [http://www.chem.qmul.ac.uk/iupac/stereo/RS.html#06 ''racemate''], [http://www.chem.qmul.ac.uk/iupac/stereo/RS.html#07 ''racemic''], [http://www.chem.qmul.ac.uk/iupac/stereo/RS.html#09 ''racemic conglomerate''] and [http://www.chem.qmul.ac.uk/iupac/stereo/RS.html#14 ''relative configuration'']. |
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| + | == References == | ||
| − | + | *Flack, H. D. and Bernardinelli, G. (1999). ''Acta Cryst.'' A'''55''', 908–915. ''Absolute structure and absolute configuration'' | |
| + | *IUPAC (1996). ''Basic Terminology of Stereochemistry.'' http://www.chem.qmul.ac.uk/iupac/stereo | ||
[[Category:Fundamental crystallography]] | [[Category:Fundamental crystallography]] | ||
Latest revision as of 13:16, 26 March 2019
Paramètre de Flack (Fr). Flack-Parameter (Ge). Parametro di Flack (It). フラック変数 (Ja). Parámetro de Flack (Sp).
Definition
The Flack parameter is the molar fraction [math]x[/math] in the defining equation [math]C=(1-x)X + x\bar X[/math], where [math]C[/math] represents an oriented two-domain-structure crystal, twinned by inversion, consisting of an oriented domain structure [math]X[/math] and an oriented inverted domain structure [math]\bar X[/math]. In reciprocal space, the Flack parameter [math]x[/math] is defined by the structure-amplitude equation
[math]G^2(h,k,l,x)=(1-x)|F(h,k,l)|^2 + x|F({\bar h}, {\bar k}, {\bar l})|^2[/math].
For a multidomain-structure twin of a chiral crystal structure, an equivalent Flack parameter may be calculated according to the method of Flack and Bernardinelli (1999).
See also
Related chemical terms
The IUPAC Basic Terminology of Stereochemistry contains definitions of related chemical terms of use to the crystallographer, viz: absolute configuration, chiral, chirality, chirality sense, enantiomer, enantiomerically pure, enantiomorph, racemate, racemic, racemic conglomerate and relative configuration.
References
- Flack, H. D. and Bernardinelli, G. (1999). Acta Cryst. A55, 908–915. Absolute structure and absolute configuration
- IUPAC (1996). Basic Terminology of Stereochemistry. http://www.chem.qmul.ac.uk/iupac/stereo