Questions tagged [ir-spectroscopy]

Use this tag for questions regarding the principles and application of infrared spectroscopy.

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Aromatic Overtones

For IR Spectroscopy, I noticed that there are aromatic overtones or "benzene fingers" a bit below the $\mathrm{2200~cm^{-1}}$ region. Why do these occur in IR spectroscopy? And is there any way to ...
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756 views

OH band in IR of propyl ethanoate? [closed]

In lab I combined 1-propanol with acetic acid to make propyl ethanoate. I obtained an HNMR and an IR of the product. The HNMR suggests that the product was successfully synthesized. The IR has the ...
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Help interpreting IR spectrum

Whilst attempting to create salicylic acid/2-hydroxybenzioc acid, one of our experiments produced a compound with a melting point of over $300^\circ\mathrm{C}$ ( as high as the machine would go) and ...
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Rotational Constant for CO2 from an IR Vibrational-Rotational spectra

I have been trying to calculate the rotational constants ($B$) for $\ce{CO}$ and $\ce{CO2}$ from IR Vibrational-Rotational spectra. I know that for $\ce{CO}$ the peak spacing is approximately $2B$ (...
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Identifying functional groups with labile hydrogens from IR hydrogen bonding region [closed]

Here is the $\pu{2000-4000 cm^{-1}}$ spectral region (known for showing hydrogen bonding interactions, $\ce{-H\bond{<-}X-}$) for three different compounds, each showing a different functional group:...
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878 views

Wavenumbers of cyclic ketones

Rank the compounds below in order of increasing C=O absorption frequency in IR spectrum (top - lowest wavenumber, bottom - highest wavenumber): Question: Would I count compound #1's cyclopentane or ...
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1answer
2k views

Distinction between whole molecules and functional groups in IR spectra

Are infrared spectra specific to compounds or to functional groups? For example, which of the molecules below best fits the IR spectrum shown? I'd have to say #2, which is a ketone based off of ...
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How is the position of a peak on an IR spectrum determined?

In an IR spectrum, all sources describe the position of a peak as a range. The ranges seem to be defined arbitrarily. Take, for example, the IR spectrum of ethanol (which I can't upload for some ...
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272 views

Wavenumber range reversed in IR spectroscopy

I recently stumbled upon a result table from an IR spectroscopy, that is an image full of peaks. The goal was to decide which peak belongs to which group by looking up the intervals in a related table....
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203 views

How to interpret intervals on a FT-IR spectrogram of soil samples?

I am studying to analyze the IR spectra of soil samples. And I'm interested in the question - how to interpret the intervals in (1750..1820) and (3020 ... 2820) of the two samples on the graph? The ...
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964 views

Explanation for increasing wave number trends for hydrocarbons

At my university, we had an organic chemistry exam question that stated,"The trend in the values of the ir absorbtions for the c-h bonds of methane ($\ce{CH4}$: $2995\,\mathrm{cm}^{-1}$), (ethylene: $...
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IR spectra and hydrogen bonds

Normally we see IR signals that correspond to the vibration of covalent bonds. Can a (strong) hydrogen bond (or a vibration thereof, to be precise) correspond to an IR signal as well? How about other ...
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Which resources teach spectrum analysis of NMR and IR spectra? [duplicate]

I’m looking for a textbook that can teach me NMR and IR spectrum reading and analysis. I really don't understand how to read the spectra or how to analyse them.
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What equipment is used for two-dimensional IR spectroscopy and how can the molecular structure of a compound be resolved?

On the Wikipedia page about two-dimensional IR spectroscopy it is said that 2D IR spectroscopy can be used to study the molecular dynamics with femtosecond time resolution. According to Wikipedia ...
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How to tell if a vibrational mode in benzene is IR and/or Raman active?

Consider the vibrational mode that corresponds to the boat-like bending of a benzene ring. Is it (i) Infrared active? (ii) Raman active? This question was asked in an assignment in my college. ...
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623 views

What is the signal at around 2090 wavenumbers in the nitroguanidine FTIR spectrum?

There is a signal at around 2090 apparent in the FTIR spectrum of nitroguanidine from Sigma-Aldrich (first image). It's also apparent in FTIR spectra we've taken in the lab (second image), but when ...
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2answers
10k views

Use of water in IR spectroscopy

I am familiar with the process of IR spectroscopy and the preparation of IR samples. However, I am curious as to why you cannot use hygroscopic or protic solvents for IR spectroscopy. Is it just ...
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268 views

Is it possible to detect the component of an unknown substances using FTIR?

Currently I'm doing research involving photo-polymer which contains unknown substances. Is it possible to detect each component of the substance by using FTIR? Will it be able to separate the ...
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1answer
328 views

Reasonably complete infrared spectral database with data in CSV form?

I'm currently developing a neural network that analyses IR spectroscopy signatures. I've found a very complete data set at The Spectral Database of Organic Compounds, but data is only available as ...
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287 views

S-N bond IR vibrations

I am working on organosulfur compounds where i have S-N bonding, according to literature it might be having an ir vibration of 1100cm-1, could anyone confirm it with reference. (the complete bonding ...
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Why do asymmetric stretches occur at higher wavenumbers than symmetric stretches? [duplicate]

I learned that the $\ce{N-H}$ bonds in a primary amine lead to two signals the infrared spectra at $\sim \pu{3400 cm^-1}$, one for symmetrical stretching and another for asymmetrical stretching. For ...
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598 views

Why is water's IR spectra indistinguishable from the IR spectra of a solution of glucose in water?

Anhydrous glucose has an absorption spectra (glucose IR spectra) that is quite different from the spectra of water (Liq. water absorption spectra). However, when a solution of glucose is prepared in ...
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Why is the carbonyl IR frequency for a carboxylic acid lower than that of a ketone whilst an ester is higher than a ketone

The approximate stretching frequencies are as follows: Acid: $1710$, Ketone: $1715$, Ester: $1730$ (all $\mathrm{cm^{-1}}$) This would seem to suggest that the acid decreases the carbonyl bond ...
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Why does the carbonyl group in an acid anhydride have two stretching frequencies?

The carbonyl stretching frequencies for an acid anhydride are approximately $1820~\mathrm{cm^{-1}}$ and $1760~\mathrm{cm^{-1}}$. These are both higher frequencies than a simple ketone owing to the ...
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FT-IR background lines

I started doing IR spectroscopy a few months ago and have run into the following problem: Here's the IR background that everyone knows and loves: CO2 peaks in the middle, water lines on either side. ...
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1answer
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How to determine force constant of C-C bond in ethanol?

How would one determine the theoretical force constant of the C-C bond in ethanol? We are asked to calculate the frequency of the C-C bond (theoretical), but to do this we need a force constant, which ...
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1answer
96 views

NO2 gas was detected in FTIR

We have a laser chamber full of $\ce{F2}$ gas (no air should be in the chamber) and several parts including steel, wires, ceramics, zinc.... This is for laser generation so the temperature is pretty ...
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Why do electronegative heteroatoms increase C=O stretching frequency (bond strength)

Why does a more electronegative heteroatom (i.e. $\ce{Cl}$ or $\ce{O}$) increase the stretching frequency of a carbonyl? I'd suspect it's that they donate their lone pairs and we end up with a ...
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1answer
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In infrared spectroscopy, why is there no C=C reading for E alkenes?

For the (E)-2-pentene, there was no C=C reading, about 1600. For the (Z)-2-pentene, there is a C=C. Why is there a reading on the Z but not on the E?
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Why the magnitude of dipole moment influences on FTIR % transmittance?

In 3:50 of this video two FTIR spectras are shown. He explains that the % transmittance (double bond in his example) depends on the dipole moment, $\mu = \delta \cdot d$. I understand that the ...
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1answer
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What does the peak separation of carbon dioxide IR rotational-vibrational spectrum corresponds to and why?

Spectrum of $\ce{CO2}$ at $2349\space \mathrm{cm^{-1}}$ region For some other molecules (for example $\ce{CO}$) the peak separation corresponds to $2B$ (where $B$ is the rotational constant ...
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Why do molecules have to have a change in dipole moment in order for them to be IR active?

My chemistry textbook keeps saying that in order for a molecule to be able to absorb infrared radiation, it has to have a change in dipole moment when the bond vibrates. I don't understand why that ...
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Is carbon dioxide IR inactive?

Wouldn't CO2 be IR inactive because of its non-polar bonds?
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Difference between torsion, out of plane, coplanar and perpendicular bends?

In Infrared spectroscopy, stretches are easily understandable. But, how do I visualize (or conceptually understand) the difference between dihedral (torsions), out of plane bends, coplanar bends, and ...
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Atmopsheric Gas IR-Spectra

I am looking for normal resolution IR-spectra of: $\ce{O2}$ and $\ce{N2}$ at high concentrations and; common minor gas in atmosphere: $\ce{H2O}$, $\ce{CO}$, and $\ce{CO2}$ at environmental ...
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How do I find out what benzene containing compound this is with IR and NMR?

I have the following IR and NMR of an unknown substance. Can someone tell me what is a possible structure of the compound or point me in the correct direction. So far I am thinking of a benzene ring ...
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How to identify an unknown compound with spectroscopic data?

I need some help identifying the following unknown compound. Any suggestions or hints regarding the possible compound would be highly appreciated. So far I am thinking the broad peak on the IR is an ...
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Interpretation of the following IR?

I have the following IR Spectrum that I am trying to interpret: So far I am thinking this compound have: a primary amine due to two peaks at 3624 and 3533. The sharp peak 3416 could indicate an ...

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