Page 102 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

IR-6.2 S U B S T I T U T I V E N O M E N C L A T U R E

until the outermost zone is completed. This treatment means that the numbering of the closo
parent is unlikely to carry over into the corresponding arachno system.

Example:

2. 4
3 5

1 6

2

7
arachno-B 7 H 13 (hydrogen atoms omitted for clarity)

When there is a c hoice, the molecule is so oriented that the 12 o’clock position is decided by
sequential application of the following criteria:

(i) the 12 o’clock position lies in a s ymmetry plane, that contains a s f ew boron atoms as
possible;
(ii) the 12 o’clock position lies in that portion of the symmetry p lane w hich contains the
greatest number of skeletal atoms;
(iii) the 12 o’clock position lies opposite the greater number of bridging a toms.

The use of criteria (i)–(iii) may fail to effect a d ecision, and where a s ymmetry plane i s
lacking they are inapplicable. In such cases the general principles o f o rganic numbering a re
used, such as choosing a n umbering scheme which gives s ubstituted atoms the lowest locants.

IR-6.2.3.4 Systematic naming giving hydrogen atom distribution
In open boranes each boron atom can be assumed to carry at least one t erminal hydrogen
atom. However, it is necessary t o s pecify the positions of the bridging hydrogen atoms by
using the symbol m, p receded by the locants for the skeletal positions so bridged in ascending
numerical order. The designator H is used for the bridging hydrogen atoms in the name.

Example:

1.
1

5 2

4 3

2,3:2,5:3,4:4,5-tetra-mH-nido-pentaborane(9)

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