Questions tagged [ir-spectroscopy]
Use this tag for questions regarding the principles and application of infrared spectroscopy.
138
questions
15
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1answer
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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 ...
0
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2answers
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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
98 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
98 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 ...
2
votes
1answer
77 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 ...
0
votes
0answers
15 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
50 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
vote
0answers
13 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. Ī½(CO) and Ī½(Fe-CO). And if there is, then ...
0
votes
1answer
21 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
38 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 ...
1
vote
0answers
22 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
45 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
39 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 ...
7
votes
2answers
805 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 $\ce{OāH}$ group with a $\ce{CāH}$? And then the other trough at $1700$ be a $\ce{C=O}$? ...
-1
votes
1answer
64 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 ...
0
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0answers
53 views
Estimate the relative intensities of absorption given the split in energy levels
Estimate the relative intensities at $\pu{25 Ā°C}$ 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) ...
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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 ...
1
vote
1answer
127 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 ...
1
vote
1answer
128 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
142 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 ...
0
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0answers
20 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
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0answers
1k views
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 ...
3
votes
1answer
286 views
Identify the structure of compound with CāHāā 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 ...
Mathew Mahindaratne
26.7k15 gold badges34 silver badges68 bronze badges
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
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0answers
29 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
388 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 ...
1
vote
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{...
Mathew Mahindaratne
26.7k15 gold badges34 silver badges68 bronze badges
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 ...
0
votes
2answers
107 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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0answers
111 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
115 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 ...
5
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2answers
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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 ...
4
votes
3answers
3k views
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 ...
0
votes
1answer
35 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 ...
11
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2answers
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3
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2answers
166 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
617 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 ...
Mathew Mahindaratne
26.7k15 gold badges34 silver badges68 bronze badges
6
votes
1answer
599 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
333 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
97 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 ...
1
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0answers
58 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 ...
19
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2answers
2k views
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 ...
2
votes
1answer
829 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 ...
1
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1answer
639 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
78 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}...
1
vote
1answer
32 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.
3
votes
1answer
349 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 ...
1
vote
1answer
161 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 ...
11
votes
4answers
18k views
Why are some molecules unable to absorb infrared radiation?
Methane $\ce{CH4}$ is symmetrical and non polar, and so is oxygen $\ce{O2}$. But $\ce{O2}$ doesn't absorb IR. Why is that? People say that if a molecule can change its polarity then it will absorb IR, ...
