4.15.1 how can you identify organic macromolecules

Chris P Schaller, Ph. Given its position in the periodic table, what is the charge on nitride ion? Therefore, what is the charge on tantalum in tantalum nitride? Tantalum nitride most commonly adopts a hexagonal structure.

The drawing below shows one unit cell. Place a tantalum atom in each corner of the unit cell. Tantalum nitride is a layered structure. The nitrides lie in the same planes as the tantalum atoms. Within each layer, there is one nitrogen in between each pair of tantalum atoms.

Add the nitrogens to each layer. How many tantalums are in a unit cell? Show how you know. How many nitrides are in a unit cell? Add atoms to the middle layer to balance things out. What is the coordination geometry of the atoms in the middle layer?

Heating tantalum metal under dinitrogen or ammonia leads to formation of hexagonal tantalum nitride. What if other methods could lead to other structures of the same compound? The easiest thing to do may be to compare the peak at 2 ppm in ethyl acetate with the peak at 3 ppm in TBME. They are both supposed to be 3H, so a comparison of those two integrals gives you a direct look at the ratio of molecules. For example, a ratio between the peak at 2 ppm and the peak at 3 ppm would indicate a ratio of molecules.

But what if, right before you made your NMR sample, you noticed a little schmutz on the NMR tube and decided to clean it with some acetone. As a result, you're pretty sure there is some acetone in your NMR sample. Unfortunately, that also shows up at 2 ppm, so you're not quite sure what part of the integral at 2 ppm is telling you about the acetone and what part is telling you about the ethyl acetate.

Don't worry. You can still resort to comparing the peak at 4 ppm in ethyl acetate, which you can see very clearly, with the peak at 3 ppm in TBME, also in the clear. The only trouble is that you have to take into account that one peak represents 2H per molecule and the other peak represents 3H per molecule.

You're cutting it down so you can compare it to a peak that would only represent 2H rather than 3H. You are putting it on an equal footing with the peak from the ethyl acetate, so that you can compare the number of molecules present, not just the number of H in each molecule. Suppose this students measures those two raw integrals at 4 ppm and 3 ppm, and gets values of H and 38H. Sometimes, you may be asked to express the make-up of the sample in terms of percent composition rather than as a ratio.

Converting ratios to percentages involves dividing one part of the ratio by the sum of both parts. If you have decided that you can identify two sets of peaks in the 1H spectrum, analysing them in different tables makes it easy to keep the integration analysis completely separate too ; 1 H in one table will not be the same size integral as 1 H in the other table unless the concentrations of the two compounds in the sample are the same.

However, comparing the ratio of two integrals for two different compounds can give you the ratio of the two compounds in solution, just as we could determine the ratio of benzene to acetone in the mixture described above. We will look at two examples of sample mixtures that could arise in lab. Results like these are pretty common events in the labIn the first example, a student tried to carry out the following reaction, a borohydride reduction of an aldehyde.

Notice how she calculated that ratio. She found another peak from molecule 2, the alcohol, that she was pretty sure represented the two hydrogens on the carbon attached to oxygen, the CH 2 -O.

The integrals for those two peaks are equal. They are both 2H in her table. However, she notes that within each molecule, the first integral really represents 1H and the second represents 2H. That means there must be twice as many of molecule 1 as there are molecule 2.

So there is twice as much aldehyde as alcohol in the mixture. That calculation just represents the amount of individual component divided by the total of the components she wants to compare. Another student carried out a similar reaction, shown below.

He also finished the reaction by washing with water, but because methanol is soluble in water, he had to extract his product out of the water. He chose to use dichloromethane for that purpose. This student might not get a very good grade; the sample does not even show up in the spectrum, so he lost it somewhere. But his analysis is also poor, so he will really get a terrible grade. During their reactions, they each used a different solvent. They were also able to determine that they had some leftover solvent in their samples by consulting a useful table of solvent impurities in NMR which they found in Goldberg et.

The ratio appears to be , but they represent 2 protons and 3 protons, respectively. The ratio appears to be , but they represent 2 protons and 4 protons, respectively. The ratio appears to be , and they both represent 2 protons, so the ratio of molecules is dichloromethane : ethyl propanoate. She obtained the following data well, this is a simulated spectrum. What was the composition of her product? Each of those peaks represents one proton, so the integral ratio of suggests a ratio of bezaldehyde to 1-phenylpropanol of of