For questions seeking generalised answers deduced from or composed of theories regarding the chemical reactions involved.

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1answer
25 views

Dihedral angle of gaseous and crystalline HOOH

Why does hydrogen peroxide exhibit a dihedral angle of 111.5 degrees in the gaseous state? And a dihedral angle of 90.2 degrees in the crystalline phase? I know that in general, there is likely to ...
1
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0answers
44 views

Which d orbitals of sulphur take part in the pi bonds of SO3?

In $\ce{SO3}$ 2 $p\pi-d\pi$ bonds are present. But which 'd' orbitals of sulphur take part in these $\pi$ bonds ? The answer says $d_{xy}$ and $d_{yz}$, someone also told me that crystal field ...
2
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1answer
95 views

Why do we need acid when making acetone peroxide?

Acetone peroxide is a very dangerous explosive, easily detonated by mild heating, friction or shock. It appears in form of small white crystals. This compound forms from the mixture of hydrogen ...
2
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1answer
70 views

Utility of Bent's Rule - What can Bent's rule explain that other qualitative considerations cannot?

Does Bent's rule have any utility? I got a vehement earful for "NO." Points raised by my professor: Coulombic considerations can be used to rationalize bond angles, strengths, and lengths without ...
2
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0answers
31 views

Examples of intramolecular hydrogen bonding closing bond angles

Okay, we've established that intramolecular hydrogen bonding can exist in molecules, and doesn't always serve the purpose of closing the bond angle at least relative to other stereoisomers of the same ...
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0answers
36 views

What Numerical Integration methods are used in DFT? [closed]

Finally I could figure out how to do DFT calculations from the scratch !. I am using Mathematica for that purpose and got very good results but here is the problem: For Hartree Potential Calculation ...
1
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1answer
43 views

How many empty orbitals do elements have?

A student was contemplating a question regarding elements with "no empty valence orbitals." An argument was made that elements all have infinite number of valence orbitals. Every atom basically ...
7
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1answer
92 views

Why is there sulfur in black powder / gun powder?

Black powder is composed of charcoal, sulfur and a nitrate salt. The charcoal and sulfur serve as fuel and the nitrate is the oxidizing agent. However, wouldn't it be cheaper to leave out the ...
3
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1answer
65 views

Energetic Placement of Atomic Orbitals in the HCl Molecular Orbital Diagram

How are the 3p orbitals of chlorine lower in energy than the 1s orbital of hydrogen?
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1answer
77 views

Hybridization in PH3

Does $\ce{PH3}$ exhibit $\ce{sp^3}$ hybridization? Arguments against hybridization: $\ce{PH3}$ is less basic than $\ce{NH3}$. This jibes with the supposition that $\ce{PH3}$ keeps its lone pair ...
4
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1answer
74 views

IBrF2 - van der Waals repulsions - and number of unique bond angles

I understand that the molecule $\ce{IBrF2}$ is T-shaped, with three ligand atoms and two non-bonding pairs. However, how many unique bond angles can this molecule exhibit? My professor argues for ...
6
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2answers
207 views

Are there any full worked examples of DFT calculations?

I just started learning DFT and now I am totally confused. Assuming I want to use B3LYP: \begin{align} v_s\left(\textbf{r}\right) &= v_\text{ext}\left(\textbf{r}\right) + \int d^3r\frac{n\left( ...
3
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1answer
40 views

How to obtain product ratio from energy differences via Boltzmann statistics

I am currently calculating some reactions and I would like to express the ratio of the products in per cents. I am using the Boltzmann statistic in the following way: The probability $p_j$ of a ...
6
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3answers
170 views

Do filled Orbitals also hybridize?

Recently I was watching a video on Valence Bond Theory, on the MIT Open-Course youtube channel. The teacher there said that for hybridization to occur, electron promotion from fully filled orbitals to ...
9
votes
1answer
149 views

When is it true that more nodes equals higher energy?

Consider all the MOs of some isolated molecule. (It could be a single atom too; I'll use MO to refer to AOs as well.) Number them in increasing order of the number of nodes (node = surface where the ...
4
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0answers
70 views

What stable arrangements of hydrogen-bonded water exist in the range of 4-20 water molecules?

Water clusters made up of various numbers of water molecules have been described. Are all of these structures theoretical? What experimental evidence supports any of these structures? How does the ...
0
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0answers
32 views

Schrödinger equation and wave function

What is the Schrödinger wave equation? What are radial probability functions, nodes-angular and radial and electron cloud? I am really confused with all these terms and all my book seems to offer me ...
1
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1answer
52 views

Molecular orbitals and “generalized” aufbau principle for heteronuclear molecular configurations

Is there any general ordering or rule for heteronuclear molecules like $\ce{AX_2}$, $\ce{AX_{n}}$, and their molecular bonding/antibonding configurations ($\sigma/\pi$ orbitals) accordingly to some ...
6
votes
1answer
126 views

How to make approximation of rotational partition function of diatomic linear molecules?

Using the rigid rotor approximation to the level energies, and such other appropriate assumptions, we can approximate rotational partition function, $Q_{\mathrm{rot}}$, of linear molecules as follows: ...
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2answers
62 views

Theoretical principles of molecular simulations

I am pharmacy student and would like to work in the field of drug design. We learn to work with the programs but thats not enough for me. I want to learn the theoretical principles of computational ...
2
votes
1answer
101 views

Why is N₂ stable but HCN and C₂H₂ unstable?

Compounds with triple bonds generally seem to be unstable. $\ce{HCN}$ and $\ce{C2H2}$ are high-energy, relatively short-lived molecules that will readily polymerise or react with other organic ...
0
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1answer
36 views

square planar geometry in metal complex

I don't understand what this statements wants to say, "Square planar geometry is favoured by ligands that can form pi bonds by accepting electrons from metal atoms or ions" How is this possible I ...
4
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2answers
162 views

Is there any emerged master principle in chemistry, like the theory of evolution in biology?

The question is about emergence and reductionism. Except a few exceptions such as dark matter, most phenomenon in nature could be reproduced from the standard model and general relativity up to a ...
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0answers
17 views

Cumulative Problem: Leak in the air conditioning system

A leak in the air conditioning system of an office building releases 12k of $CHF_2Cl$ per month. If the leak continues, how many kilograms of $Cl$ will be emitted into the atmosphere each year? My ...
2
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1answer
28 views

Number of collisions of particles in a box (or a sphere)

Imagine you randomly spread in a cubic space of volume $m^3$ (or in a sphere of volume $V_s$, as you prefer), $n_A$ particles $A$ and $n_B$ particles $B$. Particles $A$ are spheres of volume $V_A$ and ...
5
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1answer
66 views

Magical reaction tanks

I would be interested to know people's opinion on the following matter. Background Often, when the far-from equilibrium behaviour of a chemical reaction system is analysed mathematically (in papers ...
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2answers
123 views

Relationship between magnitudes of forward and reverse kinetic rate constants

Consider the reversible unimolecular reaction: $A \overset{k_{1}}{\underset{k_{2}}{\rightleftharpoons}} B$ We know that the forward reaction is often considerably more thermodynamically favourable ...
4
votes
1answer
133 views

What's the difference between PBE and B3LYP methods?

I can't find an answer to that question. I was told that in B3LYP, more variables implemented in the method are empirical, but I can't find anywhere if it's true, and I'm sure it's not the only ...
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0answers
24 views

TiO2 nanotube application in cement

I am perparing for a presentation on the application of TiO2 nanotubes in cement which is a recent topic in cement chemistry. Do you happen to have any papers (or know of any accessible on Internet) ...
2
votes
2answers
65 views

Semi-Infinite Potential Square Well: Negative Potential

I am having trouble with a problem involving a Semi-infinite potential square well: I have written down some notes that I added to the post. I have problems understanding the physical situation. See ...
1
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2answers
41 views

Dipole moment of symmetrical molecules

While studying dipole moment in organic chemistry, I got stuck at a particular statement written in the book : Symmetrical molecules without lone pair of electrons will have $\mu = 0.$ The ...
3
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2answers
217 views

Why does cyclopropane give bromine water test?

This question was in my exam and all I could tell was that it is related to high angle strain as the angle is $60^\circ$ in stead of required $109.5^\circ$. No book I have read mentions this. Also, ...
5
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0answers
151 views

Natural Bond Orbital (NBO) analyses: Physical significance/interpretation of E(2) 'stabilization energy'?

PREFACE: I am no expert on this topic. My questions at the bottom may be off base. I have some experience with symmetry-adapted perturbation theory (SAPT) when it comes to analyzing intermolecular ...
4
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1answer
168 views

Rate Constant Units and Eyring Equation

Rearranging the Eyring equation leads to the following: $$ ∆^\ddagger S^\circ = R \ln{\frac{k \times h}{{k_B}{T}}}+\frac{∆^\ddagger H^\circ}{T} $$ where k is the rate constant, h is the Planck ...
2
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0answers
158 views

What is the pKa of the oxonium / hydronium / H3O+ ion?

Although the wikipedia page on Hydronium indicates a pKa of -1.74, I noticed in the discussion of this page that the subject seems debated (cf. http://en.wikipedia.org/wiki/Talk:Hydronium#pKa.3F) ...
1
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1answer
49 views

How to estimate the dielectric constant of a liquid?

Are there any approximate relationships between the (static) dielectric constant of a liquid and properties of the individual molecules? For example, suppose I know the polarizability and dipole ...
3
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0answers
46 views

Correlation Diagram Doesn't Match Selection Rules?

From Miessler's Inorganic Chemistry, 5th edition, there is this correlation diagram for $d^{2}$ in a octahedral field. On the left hand side, if it's not clear, it goes (from lowest to highest): ...
5
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1answer
225 views

Why are excited Slater determinants used to describe electron correlation?

Usually the first step in describing the electronic wave function of a molecule or atom is to describe it with a single Slater determinant. I get that this is an independent particle approximation, ...
2
votes
2answers
109 views

How to properly denote imaginary magnitudes of vibrational frequencies

Vibrational frequency computations provide the magnitudes of vibrational frequencies for each vibrational mode of a molecule ($3N-6$ degrees of freedom for non-linear molecules and $3N-5$ for linear ...
1
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1answer
36 views

Polymers with no molecular mass distribution?

What sort of ideal conditions are required - theoretically - to conduct polymerization reactions to make all the macromolecules end up with exactly the same molecular mass, just like the products in ...
1
vote
1answer
245 views

Software for predicting chemical reactions

I wondered if it was possible to predict the product(s) of a reaction (or even the equilibrium) based on the reactants and the temperature/pressure. I found an answer to a similar question here: ...
2
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0answers
148 views

DFT optimization of a molecule in gaussian and find electrophilic sides [closed]

I am not a pro, but I have some experience with gaussian. For example, I can optimize a structure, calculate the frequency and rotational energies. In the lab I made a nucleophilic substitution ...
4
votes
1answer
223 views

Suggest methods and basis sets for a variety of systems

Please help me with any/all of the cases below. In the following cases, the named method and basis set are not suitable for the chemical systems. Why aren't they? Could you suggest a suitable ...
0
votes
1answer
130 views

Configuration Interaction matrix composition from electronic configurations

The six electronic configurations below could all be found in the matrix elements of the CI matrix at CISD level. How do I construct the 6 x 6 CI matrix composed of these six configurations and which ...
2
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1answer
70 views

Equilibrium: Equations with complex roots

I'm studying civil engineer in my first year. We have a course called "General Chemistry". One of the chapters was about chemical balance of a reaction (called equilibrium in English, I think). We got ...
17
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0answers
432 views

Is there a general consensus on the causes of the alpha-effect?

There have been various explanations posited for the $\alpha$-effect. The $\alpha$-effect refers to a phenomenon wherein nucleophiles with lone pairs on atoms adjacent (i.e., in the $\alpha$- ...
2
votes
1answer
69 views

An alternative basis set for analytical computation of two electron integrals

It is well known that the usage of the Gaussian basis set, in contrast to Slater basis set, leads relative simple semi-analytical expressions for the two electron repulsion integral $(ab|cd)$. Could ...
4
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3answers
275 views

LCAO (Linear Combination of Atomic Orbitals) and Phases

So when combining atomic orbitals to form molecular orbitals, you can either add the wave functions or subtract them. But at the same time, orbitals can exist in opposite phases (say one lobe of the p ...
4
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2answers
404 views

Hybridisation of the Carbon in an Carbanion

Given the carbanion, $ R_3C^- $, the carbon is $ sp^3 $ hybridized unless it is participating in resonance. This is clear from its steric number. In drawing its orbital diagram, however, I am having ...
6
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4answers
7k views

Why are sigma bonds stronger than pi bonds?

Why are sigma bonds stronger than pi bonds?