In most areas of chemistry, a bond represents an electronic association between two atoms. When drawing bonds, therefore, it is important to be unambiguous about (a) the nature of the electronic assocation -- is the bond in question a single bond, double bond, triple bond, or something else -- and (b) which two atoms it joins. Other types of bonding are also possible; delocalized and coordination bonds are discussed separately, as are bonds used to indicate stereochemistry.
Need more introduction.
Within a given structure, most bonds should be drawn using a single consistent length. Exceptions are certainly allowed, however, and are commonly seen in bridged polycyclic systems and sterically congested structures. The length used for bonds should be long enough so that the bond is clearly visible between two atom labels; bonds less than twice as long as the height of an atom label should be avoided.
| RECOMMENDED | AVOID | RECOMMENDED | AVOID |
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Most bonds should be indicated with a unbroken lines. The line should be approximately the same thickness as the stroke of the font used to depict atom labels in the structure (that is, the thickness of the vertical legs or the crossbar of a capital "H" in that font). Bonds that are more than four times as thick or less than one-quarter as thick as the atom label stroke width should be avoided.
| RECOMMENDED | AVOID | AVOID |
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The individual segments comprising a double (or triple, quadruple, etc) bond should be parallel and drawn in close proximity so that the segments are clearly associated with each other and do not form separate bonds or structural fragments. For practical purposes, separations greater than 33% the lenth of the bond should be avoided. The sidedness of double bonds is discussed separately.
| RECOMMENDED | AVOID |
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[This next section is stolen from the page on atom labels. Do we want the discussion here, there, or both?]
Atom labels should be positioned so that all bonds connecting to the atom label point directly at the element symbol of the atom to which they are bonded. The bonds should approach the label closely but should not impinge on the actual characters. Further discussion about positioning of bonds relative to atom labels is present in the section on atom labels.
By convention, unlabeled atoms are assumed to be carbons, and so terminal single bonds are assumed to represent methyl groups. Unlabeled bonds should not be used to represent unspecified or variable attachment points, as such diagrams are extremely prone to misinterpretation.
| RECOMMENDED | AVOID |
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| (representing a phenyl ligand) | (Would this represent a phenyl substituent or a toluene molecule?) |
Shorter-than-usual terminal bonds are especially problematic, as they can be confused not only with methyl groups, but also with negative charges. Bonds of this type should be strongly avoided.
| RECOMMENDED | RECOMMENDED | AVOID |
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| (representing methoxybenzene) | (representing a phenoxy ligand) | (Would this represent methoxybenzene, a phenoxy ligand, or a phenoxide anion?) |
