Following my conformational exploration of enols, here is one about a much more common molecule, a carboxylic acid.
The first search uses just Query 1, with additional constraints of no errors, no disorder and R < 0.05.
This can then be focused by combining Query 1 + Query 4, which shows a clear preference for the syn conformation.
Next, Query 1 with NOT query 2, which restricts the search to carboxylic acids that do not have contacts to the hydrogen of the OH group. This excludes carboxylic acid dimers, as shown above. The predominant hot-spot now corresponds to the anti conformation.
Again this is narrowed using Query 4, which removes almost all the syn examples.
Now using Query 3 (as shown above), which restricts the search to examples where the oxygen of the HO group is itself not in contact with an acidic hydrogen. This allows carboxylic acid dimers. This now reveals the syn preference again.
At <100K reinforces this effect.
Finally, Query 1 and NOT query 2 (no dimers) and NOT query 3, where a smaller preference for anti is seen.
So it seems that an interesting difference emerges between enols and carboxylic acids in that when no hydrogen bonding to the HO group is allowed, an anti preference emerges. The electronic origins of this effect will be probed in a future post.
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