Questions tagged [uv-vis-spectroscopy]
For questions that are related to the ultraviolet and visible spectrum of compounds, mostly due to electronic transitions between orbitals.
4
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1answer
26 views
Why is the graph of fluorescence vs. wavelength continuous?
If the emission of a photon from an excited state to the ground state occurs with a precise energy, then why is it that wavelengths that differ from lambda max have values on a fluorescence vs. ...
1
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0answers
17 views
Determination of pKa and molar absorptivity coefficient using spectrophotometry [on hold]
An indicator BPB (Brophenol Blue) is used and dissolved in solutions of various known $\mathrm{pH}$. Then, the absorbance of each solution at 590 nm was measured and the question asks for molar ...
1
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0answers
21 views
Standard Solutions for UV-Spectrophotometry
Can one use a mixture of compounds when making a standard solution for UV-Spectrophotometry. For instance, one is attempting to find the casein concentration of milk using UV-spec and they have milk ...
-1
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0answers
24 views
What is the expected product of reaction between PCC and NAC that has an lambda max at 255nm?
250 nm and 214 nm are the maximum wavelengths of n-acetyl cysteine disulfide according to this paper "On N-acetylcysteine. Part 11. Oxidation of N- acetylcysteine by hydrogen peroxide: a kinetic study ...
0
votes
1answer
42 views
Spin-forbidden transition iof bromine
In one of the lectures of my spectroscopy course, the professor claimed that there is a strong absorption band in the UV/Vis spectrum of bromine, associated with a singlet-state to triplet-state ...
3
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0answers
34 views
Nanoparticle Alloys (Gold-Silver) not forming
I have synthesised what I thought were gold-silver alloys at various different compositions.
The UV/vis data showed that nanoparticles alloys with a majority of the composition made from gold had one ...
0
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1answer
32 views
Characterisation of gold-silver alloy nanoparticle
I have various compositions of gold-silver alloy nanoparticles.
I would like to characterize my nanoparticles and confirm that they are alloys.
Aside from the qualitative analysis of the colour and ...
3
votes
1answer
95 views
Why we should concern with A∞?
To determine the order of one reactant at pseudo concentration of another reactant the plot of $\ln(A_t - A_∞)$ versus $t$ is used.
$A_t$ is absorbance of the intermediate at time $t$.
$A_∞$ is ...
-1
votes
1answer
32 views
What is the molar extinction coefficient of azorubine (carmoisine, E 122)
I'd be grateful for the molar extinction coefficient ε of azorubine at the absorption maximum (about 520 nm), with an authoritative reference.
0
votes
1answer
120 views
what the solution of this problem, negative absorbance values in UV-vis spectrum
In my project, I take the UV-visible spectrum of reaction between pyridinium chlorochromate and N-acetylcysteine. In some wavelengths, the absorbance value is negative for example it is (-0.006, -0....
0
votes
1answer
30 views
How to measure UV index? [closed]
I am a high school student so please apologise if I say something very dumb or irrelevant. I am conducting an experiment in which I want to find UV index at different points. Such as under shade, ...
2
votes
0answers
25 views
tolerable error, CASSCF simulation of UV/Vis spectrum
Please forgive my ignorance of experimental spectroscopy. I am a computational chemist, not an experimental one. My question is: what would be considered a tolerable or reasonable difference between ...
-1
votes
1answer
105 views
Slope of Graph of Wave Number vs inverse square of the principal quantum number(1/n^2) in Hydrogen Emission spectrum
What is the final expression we get for wave number in a hydrogen emission spectrum? Let us say for example from 6 to an orbit $n$. Considering that it is an emission spectrum, I think it would be ...
-1
votes
1answer
47 views
Evidence for a chemical reaction
I know that the emission of light is evidence for a chemical reaction. However, are there any instances where emission of light can also be considered a physical reaction?
0
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1answer
201 views
confusion about exocyclic double bond [duplicate]
I believe that there are only two exocyclic bonds in this structure. But in some text its mentioned as three.
can someone clarify.
5
votes
1answer
114 views
Why does benzene have 3 π–π* transitions in the UV range, but ethene, butadiene, and hexatriene each have only 1?
Are the π and π* orbitals of benzene much closer together in energy which allows for multiple transitions? Why is this not the case for hexatriene if they both contain the same number of pi bonds?
1
vote
1answer
99 views
Equation for the equilibrium constant for the hydration of carbonyls using UV spectroscopy
I was looking through the literature when I found this source:
https://pubs.rsc.org/En/content/articlepdf/1967/tf/tf9676302131
Which states that the equilibrium constant Khyd is:
Khyd = $\frac{[...
1
vote
1answer
36 views
UV Absorption of iodine with some solvent
$I_2$ in solution is typically absorbing around $525 \; nm$ this is why it appear to be magenta, I recently learn that with some solvent :
Benzene
Toluene
$o$-Xylene
$p$-Xylene
The coordination ...
0
votes
0answers
17 views
Why absorption changes in schiff-base formation? Coenzyme PLP
Pyrodoxal-5-phosphate (PLP) in enzymes form schiff-base to lysine residue. This can be detected by the change in the absorption from 390 nm to 420 nm (free PLP to stiff-base bound PLP).
I remember ...
1
vote
1answer
32 views
Angle of Light Source for Absorbance Spectroscopy
I apologize if this question is stupid, but have been puzzled by it for a few days. Say I have a spectrometer measuring in the visible light range and we're looking to measure the absorbance on a ...
1
vote
1answer
64 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 $\...
2
votes
0answers
70 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-...
3
votes
3answers
120 views
De-excitation of a molecule
In our chemistry lecture today on UV/vis-spectroscopy, we discussed the origin of colour in conjugated molecules due to electronic transitions from lower-energy molecular orbitals to higher-energy ...
4
votes
0answers
70 views
Evaluating Franck-Condon factors
Franck-Condon overlap integrals are given by $\langle\psi^e_{v_e}|\psi^g_{v_g}\rangle$, where $\psi^e_{v_e}$ and $\psi^g_{v_g}$ are the vibrational functions for the $v^{th}$ vibrational states of the ...
6
votes
1answer
95 views
Notation for excited states
I am reading some papers about quantum chemistry and in one I found a notation for excited states of a molecule that I don't understand at all.
In the picture below you can see the potential curves ...
0
votes
1answer
36 views
How to meausre ion interferences in solution?
Is there a way to quantitatively measure the interference of different metal ions in solution? I plan to measure concentration of Pb(II), Fe(II), and Cu(II) in solution together using a ...
12
votes
2answers
2k views
What is an exocyclic double bond?
I have been tasked to find the $\lambda_{\text{max}}$ of 3,4-dimethyl-1,2,3,4,4a,5-hexahydronaphthalene.
This was supposed to be fairly easy. I used the base value for homoannular diene ($\pu{253 nm}$...
3
votes
2answers
6k views
Woodward Fieser rules for dienes - non conjugated double bond as exocyclic?
When looking for exocyclic double bonds in a diene, should a double bond not connected to the conjugated system be considered?
For example, in this compound, should the marked double bond considered ...
