Hey;

I'm currently in a kinetics class and I am trying to do a prelab for a lab that we haven't learned the material for yet and I'm really stuck, and we unfortunately don't have a textbook for the class so I was hoping someone could help. We have the compound m-xylene and it gives the structure (you can get it on the internet too), first it asks how many non-equivalent protons there are...now I know the definition of non-equivalent protons but I have no idea how you can tell where the spins are equal or not...is it because it is the same element? The second question asks what coupling pattern you would expect based on the structure...now as far as I can tell it is based on the non-equivalent protons is it not? That deteremines how many peaks it has? I'm not sure. Lastly, they want a sketch of the 1H spectra showing the splitting pattern and relative position of each signal...this I'm totally lost at. I know the amount of peaks should be equal to the non-equivalent protons..or so I think..but I don't know how you would know how many bumps in the peak, or where the signals would be...I'm so lost.

See if this will help.

http://www.chem.ucla.edu/cgi-bin/webspectra.cgi?Problem=bp22&Type=H

That does help for at least seeing what the spectrum will look like, but I still don't get a few things...how do you know what the equivalent protons are? How do I know the coupling pattern? Would it be a triplet because it has 3 peaks..or is that something totally different? And how would I know the position of each signal on the spectra, I mean i would assume was a peak but how would I tell which is which? Would that mean there is 3 non equivalent protons?

I understand that you are working on a prelab for a kinetics class and need help with understanding some concepts related to NMR spectroscopy. NMR (Nuclear Magnetic Resonance) is a technique often used to analyze the structure of organic compounds. Let's go through your questions step by step.

1. How many non-equivalent protons are there in m-xylene?
To determine the number of non-equivalent protons, you need to consider the molecular structure of m-xylene. Non-equivalent protons are protons that have different chemical environments. In other words, they experience different magnetic environments due to their surrounding atoms or groups. In m-xylene, there are three different types of protons: the aromatic protons attached to the benzene ring, the methyl group protons attached to one of the carbon atoms, and the protons attached to the carbon atom in the middle of the methyl groups. Therefore, m-xylene has three non-equivalent protons.

2. What coupling pattern would you expect based on the structure?
Coupling pattern refers to the splitting of NMR signals caused by the interaction between neighboring protons. The number of peaks in a signal is determined by the number of neighboring protons (n+1 rule). In m-xylene, if we focus on the aromatic protons, they are likely to show a multiplet pattern. A typical representative coupling pattern is a doublet of doublets (or a doublet of triplets) due to interactions with the neighboring protons.

3. Sketching the 1H spectra showing the splitting pattern and relative position of each signal.
To sketch the 1H NMR spectra, you need to determine two main things: the chemical shift and the splitting pattern. The chemical shift indicates the relative position of the signal and is measured in parts per million (ppm). It's influenced by the molecular environment and can be found in literature or online databases.

The splitting pattern is determined by the number of neighboring protons. Using the n+1 rule, you can assign the splitting pattern based on the number of peaks. For example, if a proton has 2 equivalent neighboring protons, it will show a triplet (a peak with two smaller peaks on either side).

To determine the relative position of each signal, you need to consider the chemical shift values and the number of peaks in each signal. Higher chemical shift values correspond to protons experiencing a stronger electron-withdrawing environment. Multiple signals can appear at different chemical shift values and each signal represents a unique proton group.

It's important to note that the sketch will depend on the specific experimental conditions and the instrument used. You can find examples of NMR spectra online or in textbooks to help guide you in sketching the spectra.

To gain a better understanding of these concepts, I would recommend finding resources such as textbooks, online spectroscopy databases, or even consulting your instructor or classmates for further guidance.