# Tag Info

### How do I figure out how many hydrogens my compound actually has using a mass and NMR spectrum?

Being an NMR fan myself I would inspect that NMR spectrum: The integrals suggest you have 11 $\ce{^1H}$ or a multiple thereof (the number under each peak is the normalized integral, which is ...

### How do I figure out how many hydrogens my compound actually has using a mass and NMR spectrum?

I would probably also use the method Buck has suggested, but let’s say the NMR broke down or somebody is measuring a $\ce{^13C}$ of $\pu{2.5mg}$ meaning it will be blocked until tomorrow; in this case,...
Accepted

### Software to draw one-dimensional PES including vibrational energy levels

I have made this basic python 3 script which runs in a Jupyter notebook (or in Visual Studio Code). With different molecules you will need to adjust the plot scale. The first 10 levels are plotted ...
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### What exactly is the long chain band?

The 'long chain band' described in your textbook (Pavia) is actually a vibrational mode in which the terminal methyl groups are 'rocking'. This rocking mode is observed in open chain alkanes, -(CH2)...

### Is it "common practice in Fourier transform spectroscopy to multiply the measured interferogram by an apodizing function"? If so, why?

If there is a noisy signal that decays away, such as the FID in an NMR experiment, the signal to noise ratio is larger at shorter times than at longer ones where the noise remains but the signal is ...
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### Aromatic Overtones

In general there are 'fundamental' lines at frequency $v_1, v_2$ etc. Weak overtone transitions can occur for any fundamental vibration at frequency $nv_1$, $nv_2$ etc. where $n=2, 3,..$ and so on for ...
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### If vibrational modes are quantised, why is infrared spectroscopy smooth looking?

You should first have a look at the gas phase spectrum of water to convince yourself that vibrational levels are indeed "discrete". The textbook treatment of vibrating molecules assumes that there is ...

### Neither Raman nor IR Active vibrational modes

Yes it is possible. While no normal modes can be both IR and Raman active in molecules with a centre of symmetry, as mentioned in a comment molecules with silent modes exist. The easiest example is ...

### Why are there two infrared vibrational frequencies for the terminal CO ligands of Fe2(CO)9?

Despite the title of the publication, Fletcher et al. both present an IR spectrum of diiron nonacarbonyl in a matrix of ($\ce{Ar}$ + 10% $\ce{CO}$, recorded at $\pu{15 K}$) in the $\nu(\ce{C-O})$ ...

### Why does the C–C bond have extremely weak absorptions?

If we assume the simplyfied description, i.e. atoms being tethered together by springs, the spring constant allows describe where (energy wise, along the scale of wavenumbers, the abscissa in the ...
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### Raman transition and IR transition

To simplify slightly both Raman and IR spectroscopy show the vibrational modes of a molecule (though the techniques used to reveal these are very different). IR spectroscopy relies on coupling ...

### How do I figure out how many hydrogens my compound actually has using a mass and NMR spectrum?

I like both answers provided before me where one has used exclusive use of internet to suggest structure by NMR spectrum, and the other has used thorough analysis of mass spectrum. Although these two ...

### Why are there two infrared vibrational frequencies for the terminal CO ligands of Fe2(CO)9?

It basically comes down to molecular symmetry and since Buttonwood provided an answer just seconds ago, I'll leave the following as visualisations for it. An optimisation of $\ce{Fe2(CO)9}$ at the DF-...

### Why does the FTIR-ATR spectrum for hexamethylenediammonium adipate not have a peak for the N-H bond?

Your anticipation of absorption bands of $\ce{-NH2}$ close $3300\ldots \pu{3500 cm^-1}$ is about free and neutral amine. Your intended product is about an (organic) ammonium, $\ce{C-NH^+_3}$. Both ...

### Why are some molecules unable to absorb infrared radiation?

Infrared radiation is absorbed by a molecule when the frequency of the radiation matches that of one of the vibrational modes of the molecule. It is also necessary that the molecule have a vibrational ...

### Why does the carbonyl group in an acid anhydride have two stretching frequencies?

Just to add on to NotEvans's answer: The stretching frequencies of compounds can theoretically be predicted by group theory and symmetry considerations - some introduction can be found here. In ...
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### What do s, m, w, m-w, and w-s mean in the context of infrared spectroscopy?

Given the general agreement surrounding my comment on the question and the similar abbreviations and descriptions in the chart on the page linked by Tyberius in his comment, the meanings appear to be: ...

### Is it "common practice in Fourier transform spectroscopy to multiply the measured interferogram by an apodizing function"? If so, why?

Hamming apodization function is also known as a Hamming window. If you have data that looks like this: ...