Follow-up Comment #1, bug #68127 (group groff): At present, a simple bond without an explicit atom / atom group with the length scaling factor of 0.2 is about 33% shorter than the side of the cyclic templates (ring3, ring4, ...) with with scaling factor 0.3. To (continue to) use the scaling factor of 0.2 for bonds with an explicit atom / atom group, e.g.
bond 120 ; OH
appears to be well justified because of an additional analysis.
The .pdf written by the molecule editor ACD ChemSketch (version 2024.2.3;
style ACS1996) was imported in inkcape because the later allows to determine
both the position of the individual objects (starting coordinates X and Y in
the table below), as well as their dimension (height and width; all recordings
in millimetres). Apparently, the reduction of the bond length by approx. 33%
in reference to a «non-decorated bond» provides ample space that a
«decorated bond» can carry the additional string `OH`, `Br`, etc. Thus, the
extent of such a reduction seems «safe».
```
|-----------------------------+--------+---------+-------+--------+-------|
| measurement at | X | Y | width | height | ratio |
|-----------------------------+--------+---------+-------+--------+-------|
| single bond | 51.012 | 36.632 | 5.327 | 0.254 | 1.00 |
| double bond, upper stroke | 51.012 | 38.985 | 5.327 | 0.254 | 1.00 |
| triple bond, central stroke | 51.012 | 43.289 | 5.237 | 0.254 | 0.98 |
|-----------------------------+--------+---------+-------+--------+-------|
| MeF | 51.012 | 50.186 | 3.792 | 0.254 | 0.71 |
| MeCl | 51.012 | 57.912 | 3.538 | 0.254 | 0.66 |
| MeBr | 51.012 | 65.638 | 3.708 | 0.254 | 0.70 |
| MeI | 51.012 | 73.364 | 4.385 | 0.254 | 0.82 |
|-----------------------------+--------+---------+-------+--------+-------|
| MeNH2 | 51.368 | 81.090 | 3.538 | 0.254 | 0.66 |
| MeOH | 51.368 | 88.815 | 3.454 | 0.254 | 0.65 |
| MePH2 | 51.369 | 96.541 | 3.708 | 0.254 | 0.70 |
| MeSH | 51.368 | 100.267 | 3.708 | 0.254 | 0.70 |
|-----------------------------+--------+---------+-------+--------+-------|
| H2C=NH, upper stroke | 51.368 | 111.481 | 3.708 | 0.254 | 0.70 |
| CH2O, upper stroke | 51.368 | 119.207 | 3.623 | 0.254 | 0.68 |
|-----------------------------+--------+---------+-------+--------+-------|
| cyanide, upper stroke | 51.368 | 126.425 | 3.552 | 0.254 | 0.67 |
|-----------------------------+--------+---------+-------+--------+-------|
| hydroxylamine | 52.536 | 141.997 | 2.032 | 0.254 | 0.38 |
|-----------------------------+--------+---------+-------+--------+-------|
#+TBLFM: $6=$4/@2$4;%.2f
```
For now I think we do not need to think about how to instruct chem to shorten
a bond twice (example hydroxylamine) with both termini decorated by explicit
atom groups.
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