Questions tagged [ir-spectroscopy]
Use this tag for questions regarding the principles and application of infrared spectroscopy.
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Infrared Spectroscopy of N2O [closed]
Would you be able to identify the stretch and bend in the spectrum? I can not find much information about the $\ce{N2O}$.It's solved, does anyone know the symmetry of these vibrations?
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What is the peak at 3200 cm⁻¹ in the IR spectrum of Benzocaine?
Benzocaine has the following IR spectrum:
and here is it's structure:
From what I understand:
The two leftmost peaks are the antisymmetrical and symmetrical stretchs of the amine group.
Just before ...
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0answers
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Why is the Infrared spectrum usually drawn using transmittance rather than absorbance?
Infrared radiation can be used to identify compounds but I noticed that the spectra are usually drawn using percentage transmittance rather than percentage absorbance . Why is that ?
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structure information form IR and Raman spectra? [closed]
Is it possible to gain the idea of full molecular structure from IR or Raman spectroscopy?
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34 views
why does cyanide's IR spectrum in acetonitrile have two bands in the CN triple bond region?
I wanted to know what the CN stretching frequency of CN- in MeCN so I took a spectrum of tetrabutylammonium cyanide in transmission mode. I expected one band around 2100 but instead I got 3! So I ...
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0answers
104 views
Calculation of average bond length from force constant and IR absorption?
I need some help beginning a problem set problem (just want hints, I'd like to figure it out myself).
The problem gives me the IR absorption for a diatomic, as well as the force constant for the ...
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1answer
33 views
Is there a detailed explanation as to why polarity of a molecule affects the absorption intensity of IR radiation? [closed]
Polar molecules have an electric field due to there being a net dipole moment. The electric field will be stronger with greater polarity. The stronger electric field in the polar molecule will ...
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1answer
28 views
Determination of Urea and Hydrogen Peroxide in Cow Milk by ATR-FTIR(Attenuated total reflection-Fourier Transform Infrared Spectroscopy) [closed]
I am doing a research on cow milk adulteration. I am checking Urea and Hydrogen Peroxide content in milk by ATR-FTIR(Attenuated total reflection-Fourier Transform Infrared Spectroscopy). I am using $\...
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1answer
51 views
How do I get Mass spectrometry graph, history, and Infra-red spectroscopy graph for Secnidazole?
My chemistry teacher wants me to create an academic poster for a recently-discovered biologically important organic molecule with chirality that is relatively small and is also recent.
Secnidazole (...
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0answers
37 views
Spectral database in the UV-Vis/NIR and IR regime
I'm searching for a bunch of spectra (some tens), preferably with intense bands in the Vis spectrum, to play around with (calculating chromaticity, etc.).
They should range from
250 nm to 2500 nm (UV-...
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0answers
58 views
Creating an IR Spectrum using Gaussian ADMP Calculation
I have a Gaussian 16 trajectory for a small cluster of water molecules carried out with ADMP technique. I was wondering if anyone knows how to compute the IR spectrum from the information in the ...
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Why does the bending vibration of H2O span the A1 (rather than B1) irreducible representation?
Defining the $H_20$ molecule as being in the xz plane with the z axis being the principal axis. Why does water have a bending vibration from the $A_1$ irrep and not $B_1$? Since $B_1$ contains the $...
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1answer
299 views
How to systematically find the reducible representation of a molecule? (eg: XeF4)
I am attempting to use the reduction formula to find the irreducible representation of $\ce{XeF4}$ to determine its IR stretching vibrations. I know the point group of $\ce{XeF4}$ is $D_{4h}$ and have ...
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0answers
50 views
Beer's law relationship for light scattering at 90 degrees
First-time poster here
In Beer's law, the ratio of incident light intensity, $I_0$, to exiting light intensity, $I$, is defined as $\log_{10} (\frac {I_0} {I}) = \epsilon L c$. Then, by rearranging ...
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0answers
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Where can I find example MS, IR, NMR spectra for teaching molecular spectroscopy?
I am teaching a course on analytical chemistry, and I would like to give my students MS, IR and NMR spectra to practice with.
It would be ideal if they could analyze spectra in a more "realistic" way ...
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0answers
35 views
Absence of anti-Stokes line in Raman spectrum
If we have a molecule 1H-25X which shows a band at $3000~\mathrm{cm}^{-1}$ in the IR spectrum and you want to record a Stokes and anti-Stokes Raman spectrum with a laser of 1000 nm, why is the anti-...
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What is the difference of polarizability and dipole moment? [duplicate]
One is for Raman and the other is for IR.
The words both have 'pole', so I often confused each other.
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70 views
Effect of C13 vs. C12 reduced mass on specific vibrational modes
I understand that the reduced mass of C13 will be greater than for C12, and therefore its vibrational frequency will be lower, as it is inversely proportional to the reduced mass. However, I was ...
2
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1answer
450 views
Differences between Liquid and Solid Infrared Spectrometry [closed]
In general, when should I use liquid or solid IR spectrometry to analyse my compound? What should I expect to see? Would I see higher or lower frequency, broader or narrower transitions? My specific ...
2
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1answer
50 views
Origin of broad CO stretch in infrared spectrum of tricobalt cluster
I'm quite confident that the peaks around $\pu{2000 cm^{-1}}$ are $\ce{CO}$ stretches. But I cannot find any reference on that massive broad stretch following the $\ce{CO}$ stretches. Does it have ...
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1answer
85 views
Why do the unsaturated ketones have C-O bond weaker than saturated ketones? How it is related to resonance structures?
I am studying Infrared Spectroscopy and the book says that unsaturated ketones have a carbonyl group which has weaker bond because it's more single-bond character than single bond because it has these ...
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1answer
157 views
Stretching frequency of nitro and nitrito
I got the values of the stretching frequency of nitro and nitrito ligands from this webpage.
I understand why stretching frequencies are close in nitro and well separated in nitrito. How to explain ...
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0answers
31 views
Need help with an IR spectrum (polymer identification)
I have been given an unknow polymer and I have to identify it.
DSC measurements showed no glass transition (which means it's below room temperature) and a melting temperature at around 100-120°C. So,...
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0answers
63 views
Which bands are considered significant in the fingerprint region of IR spectra?
I'm currently writing my characterisations for the experimental section of my dissertation and can't decide which peaks from the fingerprint region of my IR are worth reporting. Is there a threshold ...
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1answer
483 views
Distinguishing propan-2-ol from ethanol using IR spectroscopy
A question requires me to distinguish between propan-2-ol and ethanol from IR spectra. To me, they both look nearly identical, even though I know both of them contain the same functional group and ...
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1answer
1k views
Assignment of the IR spectrum of 2,4-pentanedione (acetylacetone)
The IR spectrum is shown here:
My assignments so far:
The 1728 and 1708 stretches correspond to $\ce{C=O}$ stretches in the keto form - the symmetric/asymmetric stretches respectively.
The 3003 ...
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1answer
167 views
In vibrational spectroscopy, what affect do overtones have on the spectra? [closed]
I've been in a lecture about vibrational overtones in anharmonic oscillators. How would these affect an IR spectrum?
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0answers
63 views
Why do strongly electronegative atoms increase the double bond character of the carbonyl group?
I was reading Solomon's Organic Chemistry, when I came across the IR Spectroscopy part. The book says that an ester shows a peak at a higher frequency than an aldehyde because the C=O bond has ...
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0answers
67 views
Theoretical limits of (NIR) spectroscopy for quantitative analysis
Edit (months later): In hindsight, I was asking about the theoretical limits of multivariate curve resolution (see Lawton & Sylvestre: Self-modeling curve resolution) in chemometric applications.
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1answer
105 views
Wavelength-dependence of refractive index in internal reflection spectroscopy?
In many literature sources (web example), only a single value for the refractive index is assumed for the infrared element, and another is typically assumed for the sample substance. However, should ...
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0answers
26 views
Trend in the infrared stretching of molecular hydrogen to group 8 transitions metals?
While going through old notes, in relation to the Dewar-Chatt-Duncanson model, it states that the stretching frequency for $\ce{N2}$ to the group 8 transition metals ($\nu(\ce{NN})$) proceeds as:
\...
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2answers
1k views
Why does an OH bond absorb a higher frequency than a CH bond?
I'm wondering why a bond between an O and an H is going to absorb a higher frequency than a bond between a C and an H (any hybridization).
O is heavier than C in terms of atomic masses, and I'm ...
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0answers
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rovibrational spectroscopy: why do intensities of rotational lines increase with J? [closed]
how and why do the intensity of rotational lines change with J value?
in the simplest terms possible please
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2answers
3k views
O-H infrared band dependence of alcohol concentration in water
With regard to IR spectroscopy, how would the O-H band change as an alcohol solution was diluted with water? I am referring to any alcohol, but for the sake of example we can use ethanol. I think ...
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1answer
807 views
In rovibrational spectra, when exactly is the Q branch forbidden?
I'm aware that the Q branch ($\Delta j = 0$) is usually not observed in rotational-vibrational spectra of diatomic molecules in the gas state, however, I've heard different things about when exactly ...
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0answers
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Are the spectra of Imidazole and N,N-carbonyldiimidazole equal?
For QC reasons, I measured an ATR spectrum of a substance suspected to be imidazole and then ran a database search in a Sigma-Aldrich library looking for hits. I got two matches: imidazole and N,N-...
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2answers
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How do IR spectrometers produce light spanning the entire infrared spectrum?
An IR spectrum covers thousands of wavenumbers, typically $\sim 4000$ to $\pu{400 cm-1}$.
How are the spectrometers able to generate different wavelengths of light covering this entire range of ...
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0answers
42 views
How to effectively induce the bending motion of carbon dioxide?
I would like to know how to effectively induce the bending motion of $\ce{CO_2}$ with femtosecond IR lasers. In other words, how to effectively populate bending vibrational states in $\ce{CO_2}$ ...
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361 views
IR spectroscopy in CCl4 Solution v/s Liquid film [closed]
Why there are differences in these spectra ? Which one is more useful and accurate ? What is the significance of using these two different methods ?
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1answer
362 views
How to determine conformation using IR
In my advisor's Ph.D. research, she used IR spectroscopy to (help) determine the conformation of a compound of interest (its structure is known.)
In organic chemistry, I learned about using IR as a ...
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2answers
156 views
Harmonic frequencies (IR) and basis set size
Usually vibrations (harmonic), derived from harmonic approximations are bigger than for experimental values. The question is, how does this depend on the size of the basis set. Many papers give that ...
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1answer
387 views
What exactly is the long chain band?
I have progressed quite enough in infrared spectroscopy, and now I'm looking at the spectrum of alkanes in detail. I found out that straight chain alkanes have this long chain band in the spectrum:
...
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3answers
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Why does the C–C bond have extremely weak absorptions?
My book, Pavia's Introduction to Spectroscopy, tells me this about the infrared spectrum of alkanes:
$\ce{C-C}$ : Stretch not interpretatively useful; many weak peaks.
This is very interesting. ...
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1answer
2k views
What do s, m, w, m-w, and w-s mean in the context of infrared spectroscopy?
I am referring to Donald Pavia's Introduction to Spectroscopy, and I found this table that tells about the intensities of the peaks of vibrations of certain bonds.
I can't understand what ...
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1answer
213 views
Where can I find (citable) FTIR spectra of CuCl and CuCl2?
I can't seem to find any published/citable infrared (FTIR) spectra in the 4000-400 cm-1 range of CuCl and CuCl2. Does anyone know of a source available, either free or paid?
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1answer
208 views
Expected accuracy of experimental IR spectra compared to literature reference
I have a table from a journal which indicated signals of an alpha chitin that I used as theoretical values. I did my own analysis to identify a chitin sample and it had signals that slightly varied ...
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1answer
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Slight FTIR band intensity changes across several different copper salt spectra: relevant for characterization?
I have several spectra of different samples which are probably all copper (neutral and/or basic) acetate(s) and which are very similar. I present them overlayed and (some of them) stacked:
My ...
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1answer
342 views
Why does nitrous oxide have 300 times the global warming potential of CO2?
Both nitrous oxide and carbon dioxide have roughly the same atmospheric lifetime (nitrous oxide slightly longer), so I thought that it would have to do with the infrared absorbance associated with ...
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1answer
775 views
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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1answer
329 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 ...
