# All Questions

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### Bonding in diatomic C2, a carbon-carbon quadruple bond?

Carbon is well known to form single, double, and triple $\ce{C-C}$ bonds in compounds. There is a recent report (2012) that carbon forms a quadruple bond in diatomic carbon, $\ce{C2}$. The excerpt ...
2k views

### How should I go about picking a functional for DFT calculations?

I've been looking to use time-dependent density functional theory, but reading the literature I keep getting overwhelmed by how many different functionals there are. How should I go about selecting ...
1k views

### 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 ...
1k views

### What is antisymmetric exchange? What is J-strain? Where does it come from?

I'm reading a paper1 by Sanakis, et al. that characterises the magnetic coupling in the $\ce{Fe3S4}$ clusters present in bacterial ferredoxin II and beef heart aconitase as arising through something ...
11k views

### Why does meltwater taste different?

I've noticed that water obtained from melting ice cubes (by keeping them in the open) tastes different from water cooled to the same temperature. Furthermore, the taste goes away if you keep it in ...
1k views

### Why is a metabisulfite / starch / HCl solution unstable?

In one variation of the iodine clock demonstration, you add two colorless solutions together and apparently nothing happens. After about 30 seconds to a minute, you get an "instantaneous" change to a ...
1k views

### How to calculate the equilibration time of two connected chambers of salt solution, initially at different concentrations?

I am trying to build a system of two connected chambers, one of which is also connected to a cuvette, so I can perform a spectrometry experiment with different concentrations of $\ce{KNO3}$ solution. ...
155k views

7k views

### Chemical compounds responsible for the colors in flowers?

I know that anthocyanins are a class of compounds responsible for the purple colors found in flower petals. Anthocyanins (also anthocyans; from Greek: ἀνθός (anthos) = flower + κυανός (kyanos) = ...
9k views

### What is the order of stability of the resonance structures of furan?

I want to know which are the most stable furan resonance structures. I know that structure number 1 is the most stable, but which one comes after?
162 views

### Can a NOESY NMR experiment be halted partway through and give meaningful results?

Some NMR experiments can be halted partway through the acquisition and still give perfectly valid results: The traditional 1H experiment for example. Others, like a Saturation Transfer Difference ...
13k views

### When we heat a borax crystal, why does it first expand and then contract?

In the borax bead test, we take a crystal of borax and then heat it. A small loop is made in the end of a platinum or nichrome wire (as used in the flame test) and heated in a Bunsen flame until ...
237 views

### Why is it so difficult to create mock NMR spectra of macromolecules?

From what I understand, if you have a NMR spectra, you can determine the structure of a macromolecule but it is very difficult to determine what the NMR spectra of an expected structure would look ...
3k views

### 13C NMR spectrum only showing solvent

This is my first time taking a $\ce{{}^{13}C-NMR}$ spectrum and while I'm aware the signal to noise ratio is much lower compared to $\ce{{}^{1}H-NMR}$, I didn't realize it was quite this bad. I took a ...
4k views

### Is the order of orientation of electron box diagrams meaningful or arbitrary?

Here is my interpretation when asked to: By drawing arrows in the appropriate boxes, complete the outer electron structures for Cu and Cu2+ I had no problem in drawing out the electron structure, ...
10k views

### 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?
40k views

### 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 ...
9k views

### What open-source software can produce 3D PDF representation of molecules?

Most of the existing software I know (like VMD or Pymol) say that they can be used to create PDF files with 3D representations of molecules: actual 3D models, which you can rotate inside the Adobe ...
474 views

### Regenerating the imaginary data of a 2D NMR spectrum with a hilbert transform

2D spectrum take up a large amount of hard disk space. At my last lab it was standard practice to delete the imaginary portions of the spectrum with xfb n (We used ...
4k views

### What is a rigorous definition of gas volume, and how is the Van der Waals equation derived?

I am confused about the justification for the corrections to the ideal gas law in the Van der Waals equation: $$p=\frac{nRT}{V-nb}-a\left(\frac{n}{V}\right)^2$$ I understand that the equation ...
5k views

### Hanging a spoon on the face

Well, I have seen many comical acts where people balance a spoon (or a fork) on different parts of the face like on the tip of the nose, forehead etc. The do this by blowing moist air (see below) and ...
4k views

### How do copper sulphate and the like change crystal structure on adding water of hydration?

Copper sulphate, in its hydrated form, is crystalline, whereas the anhydrous form is amorphous. Gypsum has a similar story-- on heating the crystalline dihydrate we get an amorphous hemihydrate. (...
5k views

### 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 ...
10k views

### What organic solvents are suitable to use with potassium permanganate?

I'm attempting to oxidize a substance with potassium permanganate and I was wondering what organic solvents I have at my disposal. The compound is soluble in chloroform and ethanol, but obviously ...
2k views

### What does this lambda–sigma notation mean?

I am currently reading the CRC Handbook of Phosphorus-31 Nuclear Magnetic Resonance Data by John C. Tebby (CRC Press, 1991) and on several figures (ex. pages 9 to 14) there is a caption that reads ...
8k views

### Why is arsenous acid denoted H3AsO3?

Inspired by this question, I'm wondering why arsenous acid is frequently denoted $\ce{H3AsO3}$, as opposed to $\ce{As(OH)3}$, which would appear to more accurately reflect its connectivity?  I ...
251 views

### Rock that transfers image

This is a question that has been bugging me for over 15 years! In high school while studying elements our teacher showed us a clear white rock or element. It was simply flat on both sides but when ...
105k views

### How do I calculate the degree of dissociation in equilibrium?

In my textbook, for calculating the percentage dissociation of $\ce{HF}$ for the given equation: $$\ce{HF + H2O <=> H3O+ + F-}$$ The solution is: Initial Concentrations [\ce{HF}] = 0.08~\...
477 views

### What is the timescale of disulfide bond formation?

What is the timescale of disulfide bond formation in a given protein? What influences it? Finally, how does one actually measure it? From what I understand, the reduction and oxidation of bonds ...
27k views

### What are the differences between the HMQC and HSQC experiments?

This afternoon, I was having some trouble with an HSQC (Heteronuclear Single Quantum Coherence Spectroscopy) spectrum I was trying to acquire, and the spectroscopist recommended I try HMQC (...