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G R A M  M  A R                                                    I  R-2.15





           IR-2.15.3   Other ordering rules

           IR-2.15.3.1  Element ordering on the basis of the periodic table
                       One important element sequence based on the periodic table is shown  i n  T  able VI. The
                       element columns (1 to 18) are connected  b y  a rrows leading in a  d irection starting from
                       the less metallic elements and moving towards  t he more  m  etallic elements. Only H  h as a
                       unique  p osition. This order has its origin in electronegativity considerations even though O
                       is now placed at its usual position in group 16. It is used for ordering  e lement symbols and
                       element names in the following cases.
                       (a) In compositional names of binary compounds and corresponding formulae, the element
                       encountered last when  f ollowing  t he arrow in Table VI is represented first in the formula
                       as well as the name.

                       Examples:

                           1. S 2 Cl 2 disulfur dichloride
                           2. O 2 Cl dioxygen chloride
                           3. H 2 Te dihydrogen telluride
                           4. AlH 3 aluminium trihydride

                       (b) In additive names of polynuclear compounds, the central atom encountered last when
                       following the arrow is listed first, cf. S ections IR-7.3.2 and IR-9.2.5.1.

                       (c) In additive names for chains and rings, to determine the numbering of the skeletal atoms
                       if this is not defined fully by the structure of the skeleton. The element encountered first
                       when following the arrows in Table VI is given the lowest number. Note that the element
                       ‘y’ terms (Table X) are cited alphabetically.

                       Example:
                           5. HOS(O) 2 SeSH
                              1,4-dihydrido-2,2-dioxido-1-oxy-3-seleny-2,4-disulfy-[4]catena
                       (d) In Hantzsch–Widman  n ames, the element encountered first when  f ollowing the arrows in
                       Table VI is given the lowest number. The element ‘a’ terms (Table X) are cited in the same
                       order.

                       Examples:

                           6:                1                     7:           1
                                        4    O    2                        4   O    2
                                       HSb        SbH                    HSb        SbH
                                             S                                 Se
                                             3                                  3
                                   1,3,2,4-oxathiadistibetane       1,3,2,4-oxaselenadistibetane

                       (e) In names where heteroatoms replacing  s keleton atoms are indicated by ‘a’ prefixes, the
                       element encountered first when following the arrows in Table VI is given the lowest number.
                       The element ‘a’ terms (Table  X  )  a re cited in the same  o rder.


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