Questions tagged [ir-spectroscopy]
Use this tag for questions regarding the principles and application of infrared spectroscopy.
114
questions
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Do the spectra of compound materials combine linearly with respect to the ratios of the constituent compound spectra?
My question stems from reading this article on the FTIR spectrum of oil that has been mixed with various contaminants.
If one has the spectrum for the original uncontaminated oil and the spectrum for ...
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0answers
28 views
Aromatic Stretches C=C in Salicylamide
I want to ask a question about the C=C streching modes of Salicylamide.
I was presented with the following spectra and asked to comment on the bonds causing the peaks.
I identified the molecule ...
3
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0answers
42 views
Why does the binding of DMSO to metal via the S atom (k-S) strengthens the S=O bond?
So, DMSO (dimethyl sulfoxide) can form metal complexes in both $\mathrm{\kappa O}$ and $\mathrm{\kappa S}$ mode i.e. binding with the oxygen or the sulfur respectively. The general explanation given ...
0
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1answer
28 views
Near-IR spectroscopy measures the broad overtone and combination bands of some of the fundamental vibrations (only the higher frequency modes)
I am currently studying the textbook Infrared and Raman Spectroscopy by Larkin. In the first chapter of the textbook, the author opens (probably prematurely) with the following statement:
Near-IR ...
3
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2answers
85 views
H-NMR with 10H integration?
I have the following two spectra (IR and 1H-NMR) see below.
The chemical formula is: C16H16O2
Thus DBE = 9
My approach:
From the IR, I can see that there's no broad peak around 2500-3300, thus I ...
9
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3answers
554 views
How do I figure out how many hydrogens my compound actually has using a mass and NMR spectrum?
Question 3:
It said $m/z = 122,$ and $m/z = 124$ is in a $3:1$ ratio, so I figured that meant that chlorine is present. Then I thought $m/z$ was the actual compound's molecular mass.
So I used ...
6
votes
1answer
387 views
Neither Raman nor IR Active vibrational modes
Is there any molecular vibrational mode (or activity) that is neither Raman nor IR active?
In other words. Is there any activity in the molecules that can't be captured by either Raman spectrometer (...
2
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2answers
192 views
Why does the dipole moment of molecules go from positive to negative? [duplicate]
In physics the dipole moment is said to go from the negative to the positive pole, check for instance https://en.wikipedia.org/wiki/Electric_dipole_moment (Elementary definition).
This makes sense ...
0
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2answers
81 views
Could dimerization account for weak IR signals?
How would you interpret the IR spectrum of your product if it's peaks match the literature spectrum, but the signals are weak? Could the argument that the sample was very dilute and lots of water was ...
0
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0answers
19 views
How can I determine the type of IR active mode on a complex molecule from molecular geometry arguments?
I am trying to synthesize 2,6,9,10-tetracyanoanthracene and I need to discriminate it from other regioisomers. I am hoping to take advantage of the C2h symmetry under an IR spectrometer.
I like to ...
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0answers
45 views
Increase of peak intensity in case of hydrogen bonding
Typical motif in case of hydrogen bonds is charge transfer from electron rich acceptor Y to (usually) anti-bonding X-H Ļ* orbital. If so, the X-H bonding distance increases, bond weakens, stretching ...
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2answers
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Why does the weaker CāH bond have a higher wavenumber than the C=O bond?
My understanding is that a stronger bond has a higher wavenumber in IR spectrum. But why does the CāH vibration have a higher wavenumber than the C=O vibration? The latter is a double bond, so I think ...
0
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0answers
27 views
FTIR Band of C-C
I am looking at FTIR tables, and no one list aliphatic C-C bonds. Why?
If e.g. I have a spectrum of a short alkane, won't I see a vibration mode of the C-C bonds??
Thanks.
1
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1answer
220 views
Why do Ketones Have Lower Wavenumbers than Esters?
The average wavenumber for a ketone is about $\pu{1720 cm-1}$ and the average wavenumber for an ester is about $\pu{1740 cm-1}$. This, however, does not make sense, as the carbonyl group of an ester ...
1
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1answer
58 views
CO-vibration in metal carbonyl
I'm struggling to understand the trend of $\ce{CO}$-vibration in isoelectronic metal carbonyls.
$$
\begin{array}{lr|lr}
\hline
\text{Compound} & Ī½/\pu{cm-1} & \text{Compound} & Ī½/\pu{cm-1}...
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1answer
29 views
Where can I find the positions of the infrared band for phosphorus compounds in general? Specifically sodium hexametaphosphate [closed]
Specifically I am looking for the IR of the sodium hexametaphosphate compound.
2
votes
1answer
142 views
Why is UV-Vis Spectroscopy not like IR Spectroscopy
UV/Vis Spectroscopy is where electromagnetic radiation in the UV to Visible range is shone at a sample to be analysed. The absorbance of each wavelength is recorded and then plotted (very similar to ...
5
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2answers
182 views
If vibrational modes are quantised, why is infrared spectroscopy smooth looking?
I have heard that the vibrational energy level in a molecule is quantised. However, when looking at the infrared spectroscopy graph, the curves look highly continuous and smooth - not something I ...
3
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0answers
32 views
Ozone cross-section in the near-infrared
I am searching for ozone absorption cross-section in the wavelengths range 1.1 Ī¼m to 10 Ī¼m. So far I looked in the following databases:
HITRAN
Max-Planck Institute for Chemistry Mainz
and of ...
1
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0answers
25 views
Alkyl insertion with cobalt and CO
Reaction of $\ce{(Cp)Co(Me)2(CO)}$ in the presence of excess $\ce{CO}$ yields two different organic products, $\ce{A}$ and $\ce{B}.$ The only metal-containing product is $\ce{(Cp)Co(CO)2}.$ The IR ...
3
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1answer
181 views
Can anyone help me with this question on vibrational modes of free base porphyrin (C20H14N4)?
4 a. The structure of free-base porphyrin $(\ce{H2P}$, chemical formula: $\ce{C20H14N4})$ is shown below. Given that this molecule belongs to the $D_\mathrm{2h}$ point group (character table given ...
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0answers
24 views
Is there a simpler way to detect alcohol in a blood sample using IR spectroscopy?
I have seen all sorts of ways to detect alcohol using NIRS (Near InfraRed Spectrscopy) or FTIR, but they are all quite complicated in that they are using and analyzing a very wide spectrum. In ...
0
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2answers
103 views
What am I doing incorrectly with this IR/ Mass spec data? [closed]
Hello, I am trying to determine the chemical formula for the following compound. From the IR spec, I see there is a carbonyl present. Moving on to the mass spec, I see an M+ peak of 142, with what ...
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1answer
148 views
How can one distinguish an IR spectroscopy alcohol band on an organic molecule versus the alcohol bands from water in the sample?
I'm reading this IR spectra and trying to determine if the large broad band at 3388 is alcohol from an intermediate or from water in the sample. The details of the reaction, conditions, and mechanism ...
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0answers
210 views
Distinguish 1-bromobutane and 2-bromobutane with IR
How can I distinguish 1-bromobutane and 2-bromobutane by their IR spectrums?
In the 1-bromobutane spectrum I think the $\ce{-CH3}$ peak is shorter, but I don't know if that is actually reasonable or ...
17
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5answers
4k views
Is it “common practice in Fourier transform spectroscopy to multiply the measured interferogram by an apodizing function”? If so, why?
The recent paper in Nature Independent confirmation of a methane spike on Mars and a source region east of Gale Crater is interesting and the basis is a reanalysis of 2013 data taken by a X ...
3
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1answer
377 views
Why are N-H stretching vibrations often sharp and not broad?
It is known that hydrogen bonding results in the broadening of peaks in the infrared spectrum of a molecule. Hydrogen bonding results in a spectrum of different bond lengths with different stretching ...
2
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1answer
316 views
electron donation affecting carbonyl bond strength
I have been told that electron donation decreases carbonyl bond strength and thus decreases the bond stretch frequency, but electron withdrawal increases it.
This does not seem to make any sense as ...
2
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0answers
54 views
CO2 IR extinction coefficients near the 15 micrometer band
I have searched multiple times for a spectrum or a table of the gaseous carbon dioxide Lambert-Beer extinction coefficients in the IR Earth thermal region.
All I found was absorption spectra.
Is ...
5
votes
1answer
151 views
HCl rota-vibrational lab: ab initio simulation of rotation constants
I'm trying to set up the simulation portion of the classic undergraduate lab studying the rotavibrational spectrum of HCl and DCl. In terms of simulation (using Gaussian 16), the equilibrium ...
3
votes
1answer
211 views
Raman transition and IR transition
In a character table one can find the reducible representation of vibration of a molecule. In such a table we also see things like $xy,z,x...$. If this corresponds with an irrep we say that IR ...
9
votes
1answer
194 views
Dominant contribution of v = 0 ā v = 1 transition in vibrational spectroscopy
Recently I had studied vibrational spectroscopy using the quantum harmonic oscillator model.
After stating the gross selection rule [that vibrational oscillation demands a change in dipole moment for ...
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1answer
135 views
Which organic compound's NMR and IR are these? Can't find out. (Data available: Melting Point ~ 116 °C)
Which organic compound's NMR and IR are these? I have figured out that the compound is a 1,4 substituted benzene. And the substituents are probably not -COOH and -OH from the spectroscopy. Kindly help ...
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1answer
49 views
How to distinguish two molecules with same formula but different geometry with vibrational spectroscopy
There is a sample that we know is all made up by only one of these two molecule:
how you can see they have the same formula but two different geometries. The question is if it is possible to know by ...
0
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2answers
335 views
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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0answers
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What is the peak at 3200 cmā»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 ...
2
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0answers
79 views
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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48 views
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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0answers
495 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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votes
1answer
273 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 ...
1
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1answer
111 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
63 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 (...
2
votes
0answers
140 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-...
2
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0answers
130 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 ...
2
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1answer
4k 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 ...
3
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1answer
212 views
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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87 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-...
2
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1answer
2k 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 ...
3
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1answer
118 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
434 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 ...
