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1500 questions
53
votes
3 answers
What makes banana bonds possible in diborane?
Diborane has the interesting property of having two 3-centered bonds that are each held together by only 2 electrons (see the diagram below, from Wikipedia). These are known as "banana bonds."
I'm assuming there is some sort of bond hybridization…
jonsca
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53
votes
2 answers
What makes some metals melt at higher temperature?
I'm looking at the melting temperature of metallic elements, and notice that the metals with high melting temperature are all grouped in some lower-left corner of the $\mathrm{d}$-block. If I take for example the periodic table with physical state…
F'x
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52
votes
2 answers
What is the pH of ice?
The pH of pure liquid water depends on temperature. It is about pH = 7.0 at room temperature, pH = 6.1 at 100 °C, and pH = 7.5 at 0 °C. What happens to the pH (or to the ion product) of pure water when it freezes?
I assume that the proton transfer…
Horatio
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52
votes
5 answers
How can antibonding orbitals be more antibonding than bonding orbitals are bonding?
In molecular orbital theory, the fact that a bonding and antibonding molecular orbital pair have different energies is accompanied by the fact that the energy by which the bonding is lowered is less than the energy by which antibonding is raised,…
stochastic13
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51
votes
1 answer
How can I update a map/mesh and coordinates in a PyMol session file?
I have a PyMol session file I was using to create my figures. It contains a protein and ligand broken into several groups of atoms with a fair bit of overlap. There are also a few meshes built from a density map for a few figures.
Unfortunately, I…
Nick T
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51
votes
3 answers
Unit of the equilibrium constant: contradiction of Bridgman's theorem?
The following equation is standard in thermodynamics:
$$
\Delta G^\circ=-RT\log(K)
$$
where $K$ is the equilibrium constant. In dimensional analysis, Bridgman's theorem tells us that the argument of a transcendental function (like $\log$) must…
John Gowers
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51
votes
4 answers
Is carbon dioxide organic or inorganic?
Today in chemistry class we were discussing Organic Chemistry. We discussed what organic compounds basically are and then I asked the teacher whether $\ce{CO_2}$ is organic or not. She told that it is as it contains carbon and oxygen with a covalent…
Devarsh Ruparelia
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51
votes
2 answers
Why isn't aluminium involved in biological processes?
There are so many biological processes which are dependent upon ions of lighter metals (upper part of periodic table) such as $\ce{K+}$, $\ce{Na+}$, $\ce{Mg^{2+}}$ and even early transition elements ($\ce{Fe}$, $\ce{Mn}$, $\ce{Cu}$, $\ce{Ni}$), but…
animul
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50
votes
1 answer
Why doesn't frozen sugar solution taste sweet?
I'll try to make this as brief as possible:
Dissolved two teaspoons of table sugar (sucrose) in about 250ml water. Sipped it, and as expected it tasted sweet. I let the rest of it sit in the freezer overnight. Next day, I took out the frozen sugar…
paracetamol
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50
votes
1 answer
Why does menthol (e.g. peppermint) feel cool to the tongue?
Especially when drinking water after the fact, mint can give a sharp cold sensation inside one's mouth. What process causes the sensation to occur?
Daniel
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50
votes
2 answers
How does chloroform degrade nitrile gloves?
Many of us have experienced the failure of nitrile gloves when exposed to chloroform. What's going on at a mechanistic level when this occurs?
I would guess that the chloroform dissolves some of the polymer into its constituent monomers, but I've…
Pat
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50
votes
2 answers
Why is an S-S bond stronger than an O-O bond?
I'm wondering why exactly the single bond between two sulfur atoms is stronger than that of two oxygen atoms. According to this page, an $\ce{O-O}$ bond has an enthalpy of $142~\mathrm{kJ~mol^{-1}}$, and a $\ce{S-S}$ bond in $\ce{S8}$ an enthalpy of…
M.A.R.
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50
votes
6 answers
Is there any substance that's a 4-4-4 on the NFPA diamond?
A lot of the organometallics are rather... interesting compounds to work with. The most famous (among those who care, anyway) is tert-butyllithium or t-BuLi. It is the textbook example of a pyrophoric substance, demonstrated to pretty much every…
KeithS
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50
votes
3 answers
What is the reason for the exceptional stability of the cyclopropylmethyl carbocation?
Can someone explain this to me by drawing resonance structures for the cyclopropylmethyl carbocation please?
Also one more question, is the tricyclopropylmethyl carbocation more stable than tropylium ion?
Shubham
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50
votes
6 answers
Why does wood burn but not sugar?
Fundamentally, they're both carbohydrates, although the cellulose in wood is essentially polymerized glucose, which combined with its isomer fructose forms sucrose.
So why does wood readily burn while table sugar chars?
SwagMcMuffins
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