"Bond order" is certainly an ambiguous term. Within in some simple models one has just simple 0.5, 1.5, 2.5. Within more sophisticated models even "1" bond order is seen as a crude approximation. Unless someone comes up with a color code for fractional bond order (could be cool, by the way), I think Jmol must err in the "simple" direction.
0.5
I could imagine wanting to show 0.5-bond order if the desire is to depict a transition state such as:
A: + B---C --> [ A- -B- -C] --> A---B + :C
where B has two partial bonds in that middle structure. This is certainly very common.
1.5
One can certainly imagine wanting to show a system:
X==Y---Z
with 1.5 partial bond order between XY and YZ.
2.5
In the transition state for the Diels-Alder reaction of an alkyne with a diene I could imagine that one might want to depict a 2.5 bond between the two carbon atoms of the alkyne in this transition state.
3.5 is probably a stretch; there are certainly known compounds with 4.0 bond order. These are metal-metal (tungsten-tungsten) compounds, I think.
None of these are "aromatic" -- implying delocalization in a ring, as you state, Miguel. "Aromatic" is just a subset of "delocalized" so I would think simply giving a number rather than the word "aromatic" would be better. As for H-bonds, if it's easy to implement, great, otherwise just use 0.5.
Bob
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Robert M. Hanson, [EMAIL PROTECTED], 507-646-3107 Professor of Chemistry, St. Olaf College 1520 St. Olaf Ave., Northfield, MN 55057 mailto:[EMAIL PROTECTED] http://www.stolaf.edu/people/hansonr
"Imagination is more important than knowledge." - Albert Einstein
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