[Snakefingers13]

Hi,
I'm currently studying NMR as part of A2 Chemistry, and I've just got to the point of learning about TMS (or tetramethylsilane) being used as a standard substance.

One of the reasons it is chosen is due to it having a single environment for it's carbon and hydrogen atoms, but that got me thinking:

Doesn't methane have a unique carbon and hydrogen environment? If so, why is that not used as a standard substance?

If somebody could answer this, I'd be very grateful.


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[gingerbreadman85]

TMS appears at a chemical shift that is significantly different to that of other organic compounds. It means you dont have proton signals from the standard substance interfering with the rest of the spectra. Methane would mask signals from CH3 peaks and mess up integrations.

TMS is also a liquid at room temperature, dissolves readily into organic solvents and due to it's high volatility is easily recovered afterwards.

[Snakefingers13]

That makes sense.

Thanks very much!


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[cpchem]

(Original post by gingerbreadman85)
TMS appears at a chemical shift that is significantly different to that of other organic compounds. It means you dont have proton signals from the standard substance interfering with the rest of the spectra. Methane would mask signals from CH3 peaks and mess up integrations.

TMS is also a liquid at room temperature, dissolves readily into organic solvents and due to it's high volatility is easily recovered afterwards.

I wouldn't say it's significantly different in terms of chemical shift, but then I work with silanes almost every day

Another advantage with TMS... you can also use it to reference ²⁹Si NMR!

[gingerbreadman85]

(Original post by cpchem)
I wouldn't say it's significantly different in terms of chemical shift, but then I work with silanes almost every day

Another advantage with TMS... you can also use it to reference ²⁹Si NMR!

True, however that is a little niche!

Then again, I was more on the drug synth end of organic chemistry.

[Snakefingers13]

Just as an aside, my textbook says that deuterated solvents are used in 1 H NMR. Are they also commonplace in 13C, or is something else used?


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[gingerbreadman85]

Most solvents are organic, so have 13C and appear as a signal on the NMR spectra (unless you are using D2O), though the signal would be messier if it did have 1H as well. 13C NMR is almost always proton decoupled though - giving the shifts of the carbons without any multiplicities from the coupling of them with adjacent 1H.

Personally, at uni I usually ran a sample for both 1H and 13C at the same time, so would use a deuterated solvent anyway.