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Why does the energy gap for π - π* transitions shrink with the size of the pi-conjugated system?
Quoting from this site:
As conjugated pi systems become larger, the energy gap for a π - π* transition becomes increasingly narrow, and the wavelength of light absorbed correspondingly becomes longer. The absorbance due to the π - π* transition…
user4717
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Is it possible for a substance to absorb a longer wavelength of EM wave and emit a shorter wavelength?
I know a fluorescent lamp works by emitting UV first and then the specific substance inside absorbs UV and finally emits visible light. An object may emit infrared under sunlight due to heating. But those examples are absorbing short wavelength of…
Gstestso
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Comparing acidities of substituted and aromatic carboxylic acids
When comparing the acidities of carboxylic acids, we primarily see the electropositivity of the carboxylic acid carbons, i.e. we see how effectively the negative charge on the carboxylate ion is dispersed upon ionization. Electron withdrawing groups…
stochastic13
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Theoretical basis behind orbital correlation diagram for pericyclic reactions
When discussing pericyclic reactions, the Woodward-Hoffman rules allow one to predict whether a reaction will be thermally/photochemically allowed. This has been discussed in many questions on chem.SE, but essentially boils down to the following…
NotEvans.
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Why do α-hydroxy ketones give Tollens' test?
I know that tautomerism causes the $\alpha$-hydroxy ketones to give the all the tests of an aldehyde. But how does it exactly tautomerise and what's the intermediate?
Does benzoin gives Tollens' test? If not, why? I'm really confused with this. I…
Anshuman Kumar
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Can other substances be dissolved in a saturated solution?
If I have a liter of water fully saturated with sucrose would it be possible to dissolve something like salt or any other substance in the water? Or when the solution is saturated, is it impossible to dissolve another solute in it?
Samantha Clark
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Is there such a thing as an acid without a hydrogen?
I'm in AP Chemistry and we are learning about the Brønsted-Lowry model and my teacher mentioned that "for the most part" acids have hydrogen, could there be such a thing as an acid that has no hydrogen in it?
mcchucklezz
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Why does chlorine have a higher electron affinity than fluorine?
Since fluorine has its valence electrons in the n=2 energy level, and since chlorine has its valence electrons in the n=3 energy level, one would initially expect that an electron rushing towards fluorine would release more energy, as it would land…
abhishek
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Help me identify this glassware!
I'm a freshly graduated physics and math teacher moved into a small school from the late 1920s. The equipment here is old and confusing, at the very least. I have found many things which I have never seen before. I would like some help…
Jesuspowder
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What is a good method to measure the redox potential of a cellular system?
I know how to measure the concentration of free thiols, which is reflective of the redox-potential of cellular compartment such as the cytoplasm or a lysosomes.
What other methods exist?
bobthejoe
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How does adding lemon juice to sugar make better caramel?
It's a common cooking advice: if you want a somewhat softer caramel, add some lemon juice to the sugar:
To help prevent the caramel from crystallizing, you can add an acid to the sugar before you begin: add about half a tablespoon of lemon juice to…
F'x
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How does oobleck work?
Oobleck is basically a mixture of cornstarch and water. It has the interesting property of going hard when pressure is applied. For example, it feels like a liquid when you swirl your fingers through it, but it becomes hard for a second if you punch…
ManishEarth
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Is it possible for one specific atom in a molecule to have a non-integer oxidation state?
I am wondering if fractional oxidation states of an atom are possible. I'm not referring to cases such as $\ce{Fe3O4}$ or $\ce{Mn3O4}$ where the average oxidation state is fractional, since these actually comprise a mixture of atoms which are…
Nanoputian
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How are SN2 transition states stabilised by adjacent double bonds and carbonyl groups?
It is my understanding that transition states in an SN2 reaction have some filled and some empty orbital character, as we have the backside of the C-X σ* beginning to fill with electrons from the HOMO of the nucleophile, forming a C-Nu σ bond in the…
loolipop
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What does the circle inscribed in a benzene ring represent?
I have seen benzene being depicted in two different ways:
For the right-hand structure, does the inscribed circle represent the movement of double bonds or electrons?
studentrr
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