April 3, 2008
by Arvin Moser, Team Manager, Application Scientists, ACD/Labs
A biased elucidation is an elucidation where the chemist makes certain assumptions about the data at hand based on a previous experience(s) and not deviating from it. Depending on the elucidation, it can be a good thing or a very bad thing. As a good thing, it can speed up the time spent on an elucidation. However, an incorrect assumption(s) can mean wasting time and frustration to the point of being unable to elucidate the compound.
Shown below is a correlation map for an unknown with a molecular formula of C14H9NO2. The hybridization states of all the carbons are sp2, the ring size is restricted to 5 and 6, and there is an exchangeable proton (OH or NH). How many structures can you draw that fit these restrictions? For clarity reasons, the atoms in red are the ones to be arranged.
The answer is 28.
Two answers are shown below. Which tautomer did you draw first? A common structural bias is to take the 5 sp2 carbons and the nitrogen and draw a pyridine ring – pyridine being a commonly encountered substituent. Here, structural bias for this unknown is a bad thing especially if you overlooked a possibility.
The reference listed is for the tautomer on the right side. In hindsight, it is commonly seen when a pyridine ring is conjugated with a carbonyl group(s).
TIP: The best approach is to not to encourage an outcome over another, that is, make no assumptions. For elucidations where the starting material is known, consider not viewing the starting material so as not to cloud the mind. Remember to cover all the bases so all possibilities are taken into account.