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Re: proposal for AS & AC related items



To:   Coredmg
From: H.D. Flack

As promised my proposed modifications for
chemical_absolute_configuration.
  
It seems to me that:
   chemical_optical_rotation
   reflns_Friedel_coverage
   refine_ls_abs_structure_Flack
need no modification.

What I am proposing for chemical_absolute_configuration is to change
only the _definition (the rest is unchanged). After due thought, I
realized that I can not condense the content of our two recent papers
into ten or fifteen lines, so I prefer just to give the references.

Best wishes,
  H.


data_chemical_absolute_configuration
    _name                      '_chemical_absolute_configuration'
    _category                    chemical
    _type                        char
    loop_ _enumeration
          _enumeration_detail    rm
;                                        absolute configuration
established by
                                         the structure determination of
a
                                         compound containing a chiral
reference
                                         molecule of known absolute
                                         configuration
;
                                 ad
;                                        absolute configuration
established by
                                         anomalous dispersion effects in
                                         diffraction measurements on the
                                         crystal
;
                                 rmad
;                                        absolute configuration
established by
                                         the structure determination of
a
                                         compound containing a chiral
reference
                                         molecule of known absolute
                                         configuration and confirmed by
                                         anomalous dispersion effects in
                                         diffraction measurements on the
                                         crystal
;
                                 syn
;                                        absolute configuration has not
been
                                         established by anomalous
dispersion
                                         effects in diffraction
measurements on
                                         the crystal. The enantiomer has
been
                                         assigned by reference to an
unchanging
                                         chiral centre in the synthetic
                                         procedure
;
                                 unk
;                                        absolute configuration is
unknown,
                                         there being no firm chemical
evidence
                                         for its assignment to hand and
it
                                         having not been established by
                                         anomalous dispersion effects in
                                          diffraction measurements on
the
                                         crystal. An arbitrary choice of
                                         enantiomer has been made
;
                                 .      'inapplicable'
    _definition
;              Necessary conditions for the assignment of
               _chemical_absolute_configuration are given by H. D. Flack
and
               G. Bernardinelli in Acta. Cryst. (1999). A55, 908-915 and
               J. Appl. Cryst. (2000). 33, 1143-1148.


;

-- 
Howard Flack        http://www.unige.ch/crystal/ahdf/Howard.Flack.html
Laboratoire de Cristallographie               Phone: 41 (22) 702 62 49
24 quai Ernest-Ansermet             mailto:Howard.Flack@cryst.unige.ch
CH-1211 Geneva 4, Switzerland                   Fax: 41 (22) 702 61 08

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