Questions tagged [ir-spectroscopy]
Use this tag for questions regarding the principles and application of infrared spectroscopy.
143
questions
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Why is the intensity of the IR spectra of IBr higher than that of ICl?
Why is the intensity of the IR spectra of $\ce{IBr}$ higher than that of $\ce{ICl}$?
I know that the IR spectra intensities are proportional to the derivative of the dipole moment with internuclear ...
3
votes
1answer
110 views
Comparing the zero point vibrational energies of DCl and HCl
(a) Compare the zero point energy (i.e. $E_0)$ in joules for $\ce{H^{35}Cl}$ and $\ce{D^{35}Cl}$ (assuming both are anharmonic oscillators).
(b) Explain the effect this will this have on their ...
3
votes
1answer
62 views
Why is the ester carbonyl peak in benzocaine IR spectrum so low?
Having looked at multiple IR spectra for benzocaine, I am struggling to understand why the carbonyl C=O peak is so low in the spectra compared to where an ester carbonyl group usually is on other IR ...
2
votes
0answers
28 views
Why are Methyl vibr. modes called r modes and methylene vibr. modes called d modes
I am coming from a chemical background and currently work in the field of vibrational spectroscopy. When I talk to fellow physicists or chemists I always encounter the same question. "Why are the ...
0
votes
2answers
60 views
Seeking safe, water-soluble chemicals for an IR spectroscopy experiment
I am working with a custom-built device which is intended to perform some mid-infrared chemical measurements. It consists of four thermopile sensors with optical windows. In front of each window is ...
-5
votes
1answer
134 views
Why does the infrared spectrum of HCl only have one peak? [closed]
Suggest one reason why HCl has only one peak?
Does this have something to do with fact that peaks (in IR spectroscopy) represent areas of the spectrum where specific bond vibrations occur and ...
3
votes
1answer
355 views
Identifying the molecular structure of compound with sum formula C8H14O3 formula using NMR and IR spectrometry data
I am looking to identify the molecular structure of a compound with
the sum formula $\ce{C8H14O3}$ using the NMR and IR spectrometry data below.
I was able to figure out the molecule as
My friend ...
0
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0answers
16 views
availability of database for vibrational spectroscopy
is there a database for vibrational spectrums of molecules available?
i have recently started working with fragrant molecules and I am interested in their vibrational spectrums. i am limited by the ...
2
votes
1answer
57 views
Lack of elaboration in IR spectra of compounds
I've recently started learning about IR spectroscopy, and a common trend I'm seeing in my textbook and other sources is that not all the features in the IR spectrum are explained in detail. The focus ...
1
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0answers
14 views
pH Dependency of IR Stretching Frequency in CO-binded Heme Protein
If one consumes CO, then CO binds with Heme Protein forming a Fe-CO bond. My question is if there will be any pH dependency on IR Stretching Frequency, i.e. ν(CO) and ν(Fe-CO). And if there is, then ...
0
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1answer
22 views
What functional groups can 900-2500nm IR spectrometers detect?
3700 cm-1 corresponds to about 2,700 nm
650 cm-1 corresponds to about 15,000 nm.
Many cheap IR spectrometers ($7000 or so like the ones at Stellarnet) has range of 900nm to 2400nm (or 11,111 cm-1 to ...
0
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1answer
42 views
IR absorption chart
I am taking a course in structural determination of organic compounds. Right now, we are giving the IR spectra.
I am looking for a table, as detailed as possible, of the absorptions. I hope you can ...
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0answers
24 views
How can I cluster infrared spectra?
This is sorta a cross-post from my post in StackOverflow. Although, rather than seeking help with the code I'm here asking for help with a chemical/statistical problem associated with the code.
I'm ...
-1
votes
2answers
68 views
How to determine the unknown molecule using the infrared spectroscopy?
An unknown sample was analysed using infrared spectroscopy. What is
the compound?
So I am having difficulty in using the infrared data to determine the unknown compound. I keep on misinterpreting the ...
0
votes
1answer
40 views
Does increasing the number of interferometers increase signal in FT-IR?
I'm trying to understand why most modern FT-IRs have three interferometers. Does this improve the signal in someway or does it have another effect?
1
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0answers
23 views
Using the method of differential absorption to determine the ethanol content of an unknown sample [closed]
I have completed a whole set of FITR-ATR spectra analysing 6 solutions of ethanol-water mixtures, all at different concentrations of each.
I have now been instructed to use the method of differential ...
-1
votes
1answer
99 views
Is acetylene IR active? [closed]
I've a very straight forward question, I'm confused because I've been told that a atom which has a oscillating transient/permanent dipole is IR active. But there are few asymmetric stretching/bending ...
7
votes
2answers
947 views
Why does ethylamine have two infra-red spectra? Are both correct?
The one I have in my textbook is this:
Shouldn't the first trough at $3500$ to around $3000$ mean that it's an $\ce{O—H}$ group with a $\ce{C—H}$? And then the other trough at $1700$ be a $\ce{C=O}$? ...
0
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0answers
58 views
Estimate the relative intensities of absorption given the split in energy levels
Estimate the relative intensities at $\pu{25 °C}$ of absorption originated in the ground state and the first excited state when the energy levels involved are separated by:
(a) $\pu{10000 cm^-1};$
(b) ...
-2
votes
1answer
49 views
Detecting carbon dioxide concentration using mosquito neurons
At the Mauna Loa Observatory the concentration of atmospheric carbon dioxide is measured using the absorption of infra-red light. This is a statistical technique that requires constant careful ...
2
votes
1answer
114 views
Comparison of two spectra in order to find whether the irradiated sample has significantly different resulting spectra
I would like to compare two absorption spectra ( or interferograms) and conclude whether between these two there are statistically significant differences at particular wavelength intervals. At the ...
1
vote
1answer
137 views
Methods used to compare two spectra in order to determine the effects of irradiation of sample
I would like to compare two absorption spectra (or interferograms) and conclude whether between these two there are statistically significant differences at particular wavelength intervals. At the ...
2
votes
1answer
189 views
XPS/EDS vs FTIR/Raman [closed]
So I have been studying the four methods the past couple of weeks. To my understanding, XPS is a very surface-sensitive technique. It can give information about the composition of the surface but also ...
1
vote
1answer
150 views
Can you measure an IR spectrum of a sample inside a glass vial?
If I have a sample of some compounds dissolved in water inside a glass vial (let's say quartz). Would it be possible to get a usable measurement through this glass vial without too much absorption by ...
0
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0answers
27 views
Raman or FTIR spectroscopy to identify metals?
Metals are opaque, so doesn't most of the light reflect? And does the IR source even cause vibrations in the metal?
Same goes for Raman spectroscopy, is it useful for use of metal identification?
Is ...
3
votes
1answer
371 views
Identify the structure of compound with C₉H₁₀ formula using IR and NMR data [closed]
Use IR and NMR data to define the structure of the molecule, the formula of the given structure $\ce{C9H10}.$
On what basis do we conclude that its structure is that (the answer) only? On what points ...
3
votes
0answers
19 views
Any large databases of IR Spectra that you are able to download many spectra in bulk [closed]
I am currently working on a machine learning project, in which I need access to many IR spectra, the more the better, in order to build a classifier that will used some unsupervised learning in order ...
0
votes
0answers
39 views
Explaining allene IR stretching frequency
So I was comparing the IR stretch frequency of ethyne, ethene and allene. Of course triple bond is stiffer than double bond so ethyne has a higher stretch frequency. The problem then is where allene ...
0
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0answers
908 views
The IR/ H-NMR analysis of benzophenone?
I think I have figured out the IR spectrum for benzophenone. Would it be that the sharp peak in the middle (1700 cm^-1) is for the ketone and the little peaks pass 2900 cm^-1 rang are the sp2/sp3 ...
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0answers
29 views
Which one is the correct molecule of the given properties of IR Spectroscopy?
$\ce{CH3CH=CHCO2CH3}$
$\ce{CH3COOCH=CHCH3}$
$\pu{2950 cm-1}, \ \pu{2870 cm-1}, \ \pu{1740 cm-1}$ are the observed peaks.
No peaks observed $\pu{1700-1500 cm-1}$.
The formula of the molecule is $\ce{...
2
votes
1answer
46 views
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
165 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
votes
0answers
153 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
votes
1answer
41 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
votes
2answers
208 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
699 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
775 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
votes
2answers
384 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
113 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 ...
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0answers
65 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 σ* orbital. If so, the X-H bonding distance increases, bond weakens, stretching ...
19
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2answers
2k views
Why does the weaker C–H 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 C–H vibration have a higher wavenumber than the C=O vibration? The latter is a double bond, so I think ...
2
votes
1answer
735 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
vote
1answer
87 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} & ν/\pu{cm-1} & \text{Compound} & ν/\pu{cm-1}...
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1answer
34 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
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1answer
316 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 ...
6
votes
2answers
314 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
votes
0answers
35 views
Ozone cross-section in the near-infrared
I am searching for ozone absorption cross-section in the wavelengths range 1.1 μm to 10 μm. So far I looked in the following databases:
HITRAN
Max-Planck Institute for Chemistry Mainz
and of ...
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0answers
30 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
237 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
46 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 ...
