So… today, my project was going along well until we did one final thing just to double check that all of the data fits in and as an extra measure to prove that everything is correct. This final thing gave extremely unexpected results and has completely turned my project upside down. *Cries*
My project is mainly based on Polymorphism- the ability of a solid material to exist in multiple forms. My compound (Which I will keep secret as I want to publish my results if I can!) gave an indication in NMR that there were perhaps 3 different forms of it in the bottle. My experiments were to determine the structures of these forms of the compound.
When I investigated and did a whole load of recrystallization experiments and other things, I managed to solve a structure for what we thought was one of those forms. This form kept reappearing every time I tried to recrystallize or get a different form of the compound, so we thought that it must be the most stable form. Using the newly solved structure we found the other structure which was the major component found in the bottle.
However, when we calculated a predicted NMR shift for the 2 solved structures, the second form matched the experimental data pretty well but the first form did not. This was a bit weird but there are many explanations for things like this occurring, so we tried to investigate a little bit further.
Today, we measured a DSC (Differential Scanning Calorimetry) which essentially tells us the melting point of our sample as well as any other changes in energy which could result as the sample changes to different forms as the temperature changes. This told us that the melting points of the two structures were completely different. A difference of over 130 degrees C, which is pretty massive.
I discussed what this could mean with one of the PhD students (Who I always go to for help as he knows literally everything… He’s like google for chemists) and he thought that it could be an impurity. He looked further at the compound it could be and found that the oxidised form of my compound would give extremely similar structural properties to the form that I found, the melting point was almost the same AND we deduced that the NMR shift that we would get for this oxidised form would match with the NMR shift we found experimentally.
This would explain why the calculated NMR shift for my form did not match the experimental data. It means that after all of my efforts, what we have actually found is that there is an impurity in the bottle, an impurity that is readily made in air which is why it formed in all the experiments I conducted. It’s not the end of the world, as I did manage to find the structure for my compound, it just turns out that rather than it being a polymorphic structure, it just had an impurity which is much less interesting.
It just goes to show how important it is to do all these checks and to make sure that all the data makes sense. If one thing doesn’t quite fit right, then it could mean there is a problem, as in the case of mine, where everything seemed to fit in quite well, but the DSC indicated that it couldn’t be right.