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What makes some metals melt at higher temperature? |
Many diagrams of orbitals I've seen involve electrons moving through a center point—where the nucleus is. How can this be? Clearly they don't actually pass through the nucleus, so what does happen? |
How do orbitals coexist with a nucleus? |
The $p$ orbitals, for example, have a nodal plane where the nucleus is, which means the electron density is zero there.
An orbital doesn't represent a path the electrons take when moving. An orbital is a region of probability. To make things clear and definite, when we draw an orbital we only draw the region where 9... |
*Although I can't think of any drug examples other than thalidomide, here's information on thalidomide's mechanism:*
The chiral carbon of thalidomide can tautomerize in basic conditions into an enol, which is achiral. A reversal back to the ketone results in a mix of *(R)* and *(S)* enantiomers.
![Chemical diagr... |
I think there are two properties at play here: atomic velocity and stability of the lattice structure.
Recall that temperature is a measure of the average kinetic energy of the molecules, so $v \propto \sqrt{\frac{T}{m}}$, or to achieve the same velocity, $T \propto m$. So at the same temperature, two heavier atoms ... |
>*"Both Vanadium and its 3+ ion are pramagnetic. Use electron configuration to explain why this is so"*
The electron configuration of Vanadium is :
#$[Ar]4s^23d^3$
If drawn in a box diagram, it would be shown that the electron in the $d$ orbitals aren't paired. This explains how an uncharged Vanadium is parama... |
How is Vanadium's 3+ ion paramagnetic? |
When [**N,N-dimethylaniline**][1] is reacted with $\ce{H_2SO_4}$ and $\ce{HNO_3}$ it gives mainly the *meta* product, even though $\ce{NMe_2}$ is an *ortho* / *para* directing group. Why is this?
[1]: http://en.wikipedia.org/wiki/Dimethylaniline |
>*"Both Vanadium and its 3+ ion are pramagnetic. Use electron configuration to explain why this is so"*
The electron configuration of Vanadium is [Ar] 4s<sup>2</sup> 3d<sup>3</sup>.
If drawn in a box diagram, it would be shown that the electron in the $d$ orbitals aren't paired. This explains how an uncharged Van... |
When I look around for why Copper and Chromium only have 1 electron in their outermost s orbital and 5/10 in their outermost d orbital, I'm bombarded with the fact that they are more stable with a half or completely filled d orbital, so the final electron enters that orbital instead of the 'usual' s orbital.
What I... |
Why are do elements in columns 6 and 11 assume 'abnormal' electron configurations? |
![Diagram of P orbital vs. S orbital distance from nucleus][1]
My chemistry book explains that even though electrons in the 2p orbital are closer to the nucleus on average, electrons from the 2s orbital spend a very short time very close to the nucleus (penetration), so it has a lower energy. Why does this tiny am... |
Why is the 2s orbital lower in energy than the 2p orbital when the electrons in 2s are usually farther from the nucleus? |
There are some stereochemical reactions that result in the presence of enantiomers. When moving forward with a practical organic synthesis, how does one usually separate them in order to continue with one of the enantiomers? |
How do you separate enantiomers? |
The most stable cycloheanxe form is in chair conformation but on the other hand, the bigger the side-chain of the cyclohexane is, its hydrogens become more equatorial rather than axial, which brings them closer to the cyclohexane's hydrogens.
Shouldn't they arrange in a less energetic, but a more stable conformation? |
Why bigger the side-chain is, its hydrogens tend to be more equatorial? |
The most stable cyclohexane form is the chair conformation but on the other hand, the bigger the side-chain of the cyclohexane is, its hydrogens become more equatorial rather than axial, which brings them closer to the cyclohexane's hydrogens.
Shouldn't they arrange in a less energetic, but a more stable conformation? |
>*"Both Vanadium and its 3+ ion are paramagnetic. Use electron configuration to explain why this is so"*
The electron configuration of Vanadium is [Ar] 4s<sup>2</sup> 3d<sup>3</sup>.
If drawn in a box diagram, it would be shown that the electron in the $d$ orbitals aren't paired. This explains how an uncharged Va... |
I have a solution of copper acetate and I would like to play around with the ligands to get different colors.
Background: The copper acetate was made through mixing vinegar (5% acetic acid), NaCl, and C$_{\textrm{(s)}}$. The deep blue-colored copper acetate spontaneously formed during a month in my dark storage room... |
How may copper acetate ligands be manipulated to change colors? |
When I look around for why copper and chromium only have one electron in their outermost s orbital and 5/10 in their outermost d orbital, I'm bombarded with the fact that they are more stable with a half or completely filled d orbital, so the final electron enters that orbital instead of the 'usual' s orbital.
What... |
Why do elements in columns 6 and 11 assume 'abnormal' electron configurations? |
Phosphate buffer is a common buffer in biological applications, it's especially popular for NMR. Magnesium ions are necessary for many biological systems to work, though the amount of magnesium ions you can add in a phosphate buffer is limited by the relatively low solubility of magnesium phosphate.
What I'm curious... |
I was tasked with figuring out whether Carbon or Nitrogen has a more negative electron affinity value. I initially picked Nitrogen, just because Nitrogen has a higher Z$_{eff}$, creating a larger attraction between electrons and protons, decreasing the radius, causing a higher Ionization Energy, and therefore decreasin... |
Are there any major exceptions when comparing electron affinity? |
Most periodic tables only feature one Hydrogen atom, on the top of the first group. But some, like the one I was given, also show Hydrogen in the 7th group, to left of Helium.
Why are there two Hydrogen atoms? What's the difference between the two, and why do we work with the left one more often than the right? |
Why are there two Hydrogen atoms on some periodic tables? |
I have a solution of [copper acetate][1] and I would like to play around with the ligands to get different colors.
Background: The copper acetate was made through mixing vinegar (5% acetic acid), NaCl, and C$_{\textrm{(s)}}$. The deep blue-colored copper acetate spontaneously formed during a month in my dark storage... |
I have a solution of [copper acetate][1] and I would like to play around with the ligands to get different colors.
Background: The copper acetate was made through mixing vinegar (5% acetic acid), NaCl, and C$_{\textrm{(s)}}$. The deep blue-colored copper acetate spontaneously formed during a month in my dark storage... |
Overall ring strain seems to be a big issue when it comes to organic chemistry. That is why cyclopentane may be in an "envelope form" or why cyclobutane may be in a kinked, kite form. Both of these example molecules are not planar. So, why is epoxide (oxacyclopropane) a stable molecule, if at all? |
What makes an epoxide stable? |
I have a solution of [copper acetate][1] and I would like to play around with the ligands to get different colors.
Background: The copper acetate was made through mixing vinegar (5% acetic acid), NaCl, and C$_{\textrm{(s)}}$. The deep blue-colored copper acetate spontaneously formed during a month in my dark storage... |
Well, you have to ask: *how* stable? and *compared to what*?
Peroxides, including ethylene oxide, are generally considered relatively unstable molecules, with a high chemical activity and involvement in numerous reactions, including polymerization and thermal decomposition. However, ethylene oxide does exist as a mo... |
According to [wikipedia and the references given therein][1], $\pi\cdots\pi$ stacking interactions are the result of interaction between the quadrupole moments of two aromatic rings, rationalising the stabilisation of perpendicular and offset-parallel association modes of the benzene dimer. Conventional wisdom is that ... |
Are buckminsterfullerene-corannulene complexes actually stabilised by π stacking? |
This question raises more important issues than just the technical "why methyl ester," so I'll address those too.
The easiest explanation for their focus on the methyl ester is that the ethyl ester just isn't nearly as sweet. [This report][1] says it is approximately 10x less sweet (see Table VI on page 2689 and the... |
Since the steam pressure of ammonia is higher than that of water, I would expect distillation to be a reasonable way of seperating a mixture of both.
However, in industrial applications known to me there's always a step of stripping the ammonia chemically from the vapor. Why is this necessary? |
Why is distillation no viable way to seperate ammonia from water? |
Why is distillation not a viable way to seperate ammonia from water? |
Why does for example oxygen turn into gas at a much lower temperature than water?
(Does it have anything to do with the molecular structure? A water molecule does have a more complex structure than oxygen, though the R-410A (a mixture of two gases commonly used in heating pumps) is much more complex than water, and ... |
Why does different substances have different boiling points? |
For example, why does for example oxygen turn into gas at a much lower temperature than water?
Does it have anything to do with the molecular structure? A water molecule does have a more complex structure than oxygen, though the R-410A (a mixture of two gases commonly used in heating pumps) is much more complex than... |
Why do different substances have different boiling points? |
This question raises more important issues than just the technical "why methyl ester," so I'll address those too.
The easiest explanation for their focus on the methyl ester is that the ethyl ester just isn't nearly as sweet. [This report][1] says it is approximately 10x less sweet (see Table VI on page 2689 and the... |
If dry ammonia gas is passed through anhydrous copper sulfate, will it turn blue (due to the formation of tetraamminecopper(II) complex)? Or will silver chloride form diamminesilver(I) complex in liquid ammonia?
If the above complexes do not get formed in non-aqueous mediums, why is it so? |
Is aqueous medium necessary for complex formation? if so, why? |
Over the course of my studies, I have switched largely from using Z-matrix representations of molecular geometries in calculations to Cartesian representations.
The software that I use now makes it easy to add the sorts of constraints/restraints/transits that I would have previously used Z-matrices for, and I know t... |
Pros and cons of Cartesian vs. Z-matrix representations of molecules? |
Well, you have to ask: *how* stable? and *compared to what*?
Epoxides, including ethylene oxide, are generally considered relatively unstable molecules, with a high chemical activity and involvement in numerous reactions, including polymerization and thermal decomposition. However, ethylene oxide does exist as a mol... |
Pennsylvania State University provides irradiated NaCl (180,000 rads of gamma radiation) to teachers for a very entertaining demonstration. The salt is orange after irradiation. When it is placed on a hot plate, you see a flash of visible light and the salt returns to it normal color. The explanation provided with the ... |
How is the electron "trapped in the crystal" in irradiated NaCl? |
**Cartesian Space**
In Cartesian space, three variables (XYZ) are used to describe the position of a point in space, typically an atomic nucleus or a basis function. To describe the locations of two atomic nuclei, a total of 6 variables must be written down and kept track of. The general ruling is that for Cartesi... |
What you're describing is thermoluminescence, which is used as a paleochronology method (aka Trapped Electron (TE) dating, afaik). The [wikipedia article][1] has a good synopsis. Simply, electrons get bound to potential wells generated in the radiation-defected structure. When you heat the crystal up you allow it to an... |
To my understanding, [cationic polymerization](http://en.wikipedia.org/wiki/Cationic_polymerization) is a type of [living polymerization](http://en.wikipedia.org/wiki/Living_polymerization) but my teacher's notes and Wikipedia seem to suggest they're [different](http://en.wikipedia.org/wiki/Living_cationic_polymerizati... |
I've always seen benzyne (benzene with a triple bond) classified as an 'intermediate'. I really don't see why it needs to be an intermediate, though. The possuble reasons I can come up with are flimsy:
- It has an unstable sp2-sp2 $\pi$ bent bond: We have bent bonds with more angle strain in cyclopropane, which is ... |
Why is benzyne an intermediate? |
You can buy NMR tubes in a huge variety of qualities, with an equally huge difference in price between the cheapest and the most expensive NMR tubes. They are usually rated for a specific spectrometer frequency, e.g. 300 MHz+ or 600 MHz+.
What is the difference between these different grades of NMR tubes? And how la... |
What benefits do higher-rated NMR tubes provide? |
There are two kinds of bonds **between** polymers in solid material: primary and secondary. Primary bonds can be also called cross-linked bonds. What is the difference between the two (strength, type, response to stress/strain, etc)? How do they compare to bonds inside a polymer? |
What is the difference between cross-linked bond and secondary bond in polymers? |
Intermediate is a middle step in the chemical process: reactants -> intermediate(s) -> products. Benzyne is formed from benzene and is highly reactive. Thus, it is never the first or last step of the process. To my knowledge benzyne is rarely observed as a product, because its reacting fast with other molecules because... |
A general rule is: crap goes in, crap comes out. A large-sample low-field 1D NMR at room temperature is usually only minimally affected by using a cheap NMR tube. There are important differences though and I'll highlight a few.
The first distinction between prices is what the tube is constructed from: quartz obvious... |
I've always seen benzyne (benzene with a triple bond) classified as an 'intermediate'. I really don't see why it needs to be an intermediate, though. The possible reasons I can come up with are flimsy:
- It has an unstable <em>sp</em><sup>2</sup>–<em>sp</em><sup>2</sup> $\pi$ bent bond: we have bent bonds with more... |
Intermediate is a middle step in the chemical process: reactants -> intermediate(s) -> products. Benzyne is formed from benzene and is highly reactive. Thus, it is never the first or last step of the process. To my knowledge benzyne is rarely observed as a product, because its reacting fast with other molecules because... |
**Cartesian Space**
In Cartesian space, three variables (XYZ) are used to describe the position of a point in space, typically an atomic nucleus or a basis function. To describe the locations of two atomic nuclei, a total of 6 variables must be written down and kept track of. The general ruling is that for Cartesi... |
Given an organic compound, is there any way to decide if it is volatile (or compare volatility--everything is volatile in the end)?
Volatility is due to the tendency to evaporate. The conclusion I can draw from this is that a more volatile compound will be lighter and/or will have less intermolecular forces. But thi... |
The main chemistry prep room at my institution (and also at the ambulance station) is labelled with the standard green compressed gas sign. However, there is a small '2' included within the diamond. None of the chemistry technicians, tutors or ambulance staff seem to know what it is referring to and I can't find any ... |
What is the meaning of the '2' on some Compressed Gas Hazard signs in the lab? |
To my understanding, [cationic polymerization](http://en.wikipedia.org/wiki/Cationic_polymerization) is a type of [living polymerization](http://en.wikipedia.org/wiki/Living_polymerization) but my teacher's notes and Wikipedia seem to suggest they're [different](http://en.wikipedia.org/wiki/Living_cationic_polymerizati... |
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](http://en.wikipedia.org/wiki/Diborane)). These are known as "banana bonds."
I'm assuming there is some sort of bond hybridization transpiring, but the geome... |
What makes diborane an ideal situation for banana bonds? |
Look carefully, it's (distorted) tetrahedral--four groups at nearly symmetrically positions in 3D space{*}. So the hybridization is $sp^3$.
$\ce{B}$ has an $2s^22p^1$ valence shell, so three covalent bonds gives it an incomplete octet. $\ce{BH3}$ has an empty $2p$ orbital. This orbital overlaps the existing $\ce{B-... |
To my understanding, [cationic polymerization](http://en.wikipedia.org/wiki/Cationic_polymerization) is a type of [living polymerization](http://en.wikipedia.org/wiki/Living_polymerization) but my teacher's notes and Wikipedia seem to suggest they're [different](http://en.wikipedia.org/wiki/Living_cationic_polymerizati... |
What makes banana bonds possible in diborane? |
Look carefully, it's (distorted) tetrahedral--four groups at nearly symmetrically positions in 3D space{*}. So the hybridization is $sp^3$.
![enter link description here][1]
As you can see, the shape is distorted, but it's tetrahedral. Technically, the banana bonds can be said to be made up of orbitals similar to... |
If you characterize the chemical bonds to two categories physical and chemical bonds, how do you do it? Aren't all bonds chemical **and** physical?
From the freedictionary.com, chemical bond:
Any of several forces, especially the ionic bond, covalent bond, and metallic bond, by which atoms or ions are bound i... |
What is the difference between physical and chemical bonds? |
Look carefully, it's (distorted) tetrahedral--four groups at nearly symmetrically positions in 3D space{*}. So the hybridization is $sp^3$.
![enter link description here][1]
As you can see, the shape is distorted, but it's tetrahedral. Technically, the banana bonds can be said to be made up of orbitals similar to... |
In short: the definition of a chemical bond is not unique and a clearly-drawn line. The simplest and most common definition is **the sharing of electrons between two or more nuclei**. In contrast, other interactions are often said to be *intermolecular* (which is somewhat more specific than the term “physical”.
--- ... |
In short: the definition of a chemical bond is not unique and a clearly-drawn line. The simplest and most common definition is **the sharing of electrons between two or more nuclei**. In contrast, other interactions are often said to be *intermolecular* (which is somewhat more specific than the term “physical”.
--- ... |
If you characterize the chemical bonds to two categories physical and chemical bonds, how do you do it? Aren't all bonds chemical **and** physical?
From the freedictionary.com, chemical bond:
> Any of several forces, especially the ionic bond, covalent bond, and metallic bond, by which atoms or ions are bound in ... |
[Neil Bartlett](http://en.wikipedia.org/wiki/Neil_Bartlett_(chemist))(1932-2008) first synthesized $XeF{_4}$ (and $XeF{_6}$) in 1962. In the [synthesis](http://en.wikipedia.org/wiki/Xenon_tetrafluoride#Synthesis), a nickel chamber is used, and heated to 400°C, causing the formation of $NiF{_4}$.
The $XeF{_4}$... |
What is the configuration of nickel tetrafluoride during the synthesis of xenon tetrafluoride? |
I've known that hybridization in distorted geometries is not exactly $sp^3$ or $sp^2$ or whatever. For example, [$\ce{PH3}$][1] has _nearly_ pure $p$ orbitals in the $\ce{P-H}$ bond, and the lone pair is in a _nearly_ pure $s$ orbital.
Basically, since hybridisation is an addition of wavefunctions, instead of a perf... |
[Neil Bartlett](http://en.wikipedia.org/wiki/Neil_Bartlett_(chemist))(1932-2008) first synthesized $XeF{_4}$ (and $XeF{_6}$) in 1962. In the [synthesis](http://en.wikipedia.org/wiki/Xenon_tetrafluoride#Synthesis), a nickel chamber is used, and heated to 400°C, causing the formation of $NiF{_4}$, but it not part of... |
What is the configuration of fluorine during the synthesis of xenon tetrafluoride? |
[Neil Bartlett](http://en.wikipedia.org/wiki/Neil_Bartlett_(chemist)) (1932–2008) first synthesized $\ce{XeF{_4}}$ (and $\ce{XeF{_6}}$) in 1962. In the [synthesis](http://en.wikipedia.org/wiki/Xenon_tetrafluoride#Synthesis), a nickel chamber is used, and heated to 400°C, causing the formation of $\ce{NiF{_4}}$, bu... |
[Neil Bartlett](http://en.wikipedia.org/wiki/Neil_Bartlett_(chemist)) (1932–2008) first synthesized $\ce{XeF{_4}}$ (and $\ce{XeF{_6}}$) in 1962. In the [synthesis](http://en.wikipedia.org/wiki/Xenon_tetrafluoride#Synthesis), a nickel chamber is used, and heated to 400°C, causing the formation of $\ce{NiF{_4}}$, bu... |
What is the geometric configuration of the four fluorine atoms during the synthesis of xenon tetrafluoride? |
I've always thought that orbitals lead to a loss of symmetry, and have never been able to give myself a satisfactory answer to this.
I'll explain via an example:
Let's take an $\ce{N3+}$ atom. It's perfectly spherical, and has no distinguishing 'up' and 'down'. There is no set of 'preferred coordinate axes' for i... |
Symmetry lost in orbitals? |
I've always thought that orbitals lead to a loss of symmetry, and have never been able to give myself a satisfactory answer to this.
I'll explain via an example:
Let's take an $\ce{N^3+}$ atom. It's perfectly spherical, and has no distinguishing 'up' and 'down'. There is no set of 'preferred coordinate axes' for ... |
Let's say I synthesized or isolated a chiral molecule and want to know the absolute configuration (R or S) of that molecule. I could obviously solve the structury by X-Ray crystallography, but that's a lot of work and I might not want to do that or might not have access to the necessary equipment.
What other ways ex... |
How do I determine the absolute configuration experimentally? |
I remember seeing a periodic table that had the top-left corner of the d-block shaded and marked as "brittle". If I recall correctly, the elements were $\ce{Sc,Ti,V,Cr,Mn,Y,Zr,Nb,La}$. I think (Sorry, I can't find much on it on the Net)
The triangular shaded area is a clear indicator of a groupwise and period wise... |
A Chemdrawing software? |
Besides elucidating or verifying a chemical structure, NMR can also be used e.g. for quantifying a mixture of different chemicals.
Depending on the spectrum and specific substance, integrating the NMR signals for the same molecule can result in significant variations from the actual ratio of nuclei, which is known ... |
What factors are important for quantitative analysis of an NMR spectrum? |
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