22

It's not usual to consider graphite as a material composed of "molecules" in the typical sense, though it could be viewed as a kind of polymer with two-dimensional macromolecules. Regardless, it is fruitful to analyse the individual sheets in graphite as the limit of increasingly large polycyclic aromatic hydrocarbons (PAHs). The sequence goes: benzene ($\ce{...


13

You have a possible answer to your question in proteins, an example which includes some long polymer chains. Intramolecular interactions - while not necessarily the driving force for formation of a collapsed protein globule (usually argued to be due to the hydrophobic effect, requiring intermolecular interactions) - are the basis for higher order structure ...


12

Graphite has got a structure similar to books stacked on top of each other. Multiple layers on top of each other and each layer going by the name graphene. Atoms in each individual layer is covalently bonded, which is quite strong. Remember covalent bond is the one that holds diamond together, which is one of the hardest substances. Atoms in the individual ...


9

There is no strict upper limit you can place on any type of electromagnetic interaction. That being said, van der Waal's forces are due to the formation of instantaneous dipoles which are a result of perturbations of an otherwise spherically symmetric electron density. The electric field produced by a dipole decays as $1/r^3$. Therefore, it should not be ...


9

In Principles of Nucleic Acid Structure, W. Saenger argues that hydrogen-bonded bases contain at least two hydrogen bonds (forming a "cyclic" pattern). Often, there is a tautomeric form possible that also makes two hydrogen bonds, with two covalent bonds turning into hydrogen bonds, two hydrogen bonds turning into covalent bonds, and double bonds moving ...


6

The parameter $a$ from the van der Waals equation $$\left(p+\frac{an^2}{V^2}\right)\left(V-nb\right)=nRT$$ is not to be taken only as the measure of strength of intermolecular bonding. Rather, it is overall measure of significance and frequency of intermolecular interaction. It may be based on purely elastic electrostatic interactions, where only the ...


5

London dispersion forces are instantaneous dipole-induced dipole interactions. All compounds can have an instantaneous dipole moment, including ions, so London dispersion forces exist for all compounds. Unlike molecules, ions are charged. The electrostatic interactions between charges are far stronger than the London dispersion forces between ions, so ...


5

As jheindel has previously pointed the interaction has no limit. What you are probably looking for is the distance at which the interaction energy becomes smaller than thermal energy at a given temperature. When the interaction is smaller then thermal motions govern what happens not the intermolecular interaction. Thermal energy at $300$ K is $k_BT = 1.38\...


3

The effect of intramolecular forces versus intermolecular forces on boiling and melting points is sometimes seen when we compare the boiling points of ortho- and para-nitrophenol (or similar compounds). Para-nitrophenol shows intermolecular hydrogen bonding, which causes an increase in boiling point as different molecules bond better with each other, as ...


3

Q1 and Q2 have the same approach. One notices that they are homologous alkanes and picks the biggest and the smallest, having the most London dispersion/van der Waals force and least, respectively. Other forces are known not to be present between alkanes.$^1$ (There is a small difference between branched and linear alkanes, but that is negligible compared to ...


3

In milk, casein exists as a colloidal aggregate (casein micelle) with the properties you state, but purified casein is different. It is rich in proline (shown below), has no disulfide bridges, and hence little tertiary structure to hide the hydrophobic residues in the core of the protein with the hydrophilic residues on the surface to bind to water. In ...


3

The reason why boron and carbon are solids at room temperature because of their structure. Both carbon and boron form giant covalent structures, meaning a lot of energy has to be put into break the bonds between atoms and turn into a liquid. A example of this would be diamond - here each carbon atom is covalently bonded to 4 others meaning no inter-...


3

Besides the computational methods clearly described by @Martin, you can identify hydrogen bonds using a number of experimental methods, many are indirect such as melting and boiling points, more specific are changes in absorption/fluorescence and changes in ir and raman spectra. Microwave spectra can be used in the gas phase. The best methods are ...


3

There is a paper titled "Amide-pi interactions between formamide and benzene", doi: 10.1002/jcc.21212. It has been cited by a paper on a crystal structure on a urea transporter (the interaction is between a peptide bond of a ligand and aromatic side chains of the protein). Technically, the interaction between the arginine side chain and aromatic groups ...


3

Let me crash the party here. TL;DR: Dispersion interactions are not due to fluctuating induced-dipole attractions, even if everyone tries to explain it that way. (I know that this must seem like an outrageous statement, and surely downvote fingers are itching now. Bear with me.) Based on the Hellmann-Feynman theorem, it is known that the forces acting on ...


2

A solution that has a maximum or minimum vapour pressure (vs mole fraction) is called an azeotrope. The liquid is in equilibrium with the vapour and mole fractions in the liquid are the same as in the vapour at a given temperature. As the composition of liquid and vapour are the same the $dp/dx_A=0$ where $p$ is pressure and $x_A$ mole fraction of species A....


2

Can't there ever be hydrogen bonds between 2 purines or between 2 pyrimidines? Yes, it is possible to have hydrogen-bonded base pairs (and triplets and quadruplexes) beyond the canonical Watson-Crick base pairs A:T and G:C. You can explore these in 3D on the DSSR-Jmol site for example. If you look at the 1ehz structure (a tRNA from yeast), which loads ...


2

Olive oil is a triglyceride, and the main fatty acid is oleic acid below. Now the bromine does not add to the double bond between oxygen and carbon; instead the bromine reacts with carbon-carbon double bond and add itself to it. If you use e.g. coconut oil which has minimal unsaturated (meaning having carbon-carbon double bond) fatty acids (and assume you ...


2

This is a tough question to answer because the intermolecular distances are similar in the solid to liquid transition unlike those in the liquid to gas phase transition. In the case of the elements there is a correlation between the Debye temperature and the melting temperature. The Debye temperature is that temperature at which the atoms gain their full ...


2

You are correct that simply stating that the Schrodinger equation is time dependent does not really answer the question. In fact, time-dependence is not a component of the derivation of the dispersion forces. At a surface level, they just represent how much the ground state energy of a system of polarizable molecules is lowered by their interactions. It's ...


1

Permanent Dipoles occur when two atoms bonded to each other have significantly different electronegativities. When the atomic number of an element increases the number of electrons present in them also increases. These electrons are constantly moving around in the atom. At some point, there are more electrons on one side of the atom than the other. This ...


1

Although individual dispersion forces are weak, they are cumulative, and increase with molar mass. As a general rule, boiling point increases with molar mass. Polar molecules will have higher boiling points when compared to molecules with similar molar masses. For example, ethanol($\ce{CH3CH2OH}$) has a higher boiling point than dimethyl ether ($\ce{...


1

The relatively high boiling points for such low molecular weight compounds suggests a primary effect from hydrogen bonding. Using ethanamide as a reference point, propanamide has a higher molecular weight, which should raise the boiling point a little, but three relatively nonpolar carbons (plus hydrogens) vs two in ethanamide. A lower boiling point would ...


1

I haven't done it in vmd, but a rdf is really kind of like a histogram. For a particle of interest, you count how many particles are between r and $\Delta r$ from it and record that number in a bin, then move outwards, recording numbers in each shell into a bin for that shell. That tells you the rdf of that particle interacting with everything else. If there ...


1

It is true that Q1 and Q2 can be addressed having the same approach since all of them are hydrocarbons, which do not have any other forces acting on them other than the London dispersion and van der Waals forces. Also, they are homologous alkanes, which increase those forces according to their size. Yet, these forces also depend on how branched their ...


1

This is because when these liquids are mixed, H-bonding type interactions are formed between hydrogen atom of chloroform (partial positive charge due to 3 Cl atoms) and 'pi' electron cloud of benzene ring. Thus, chloroform-benzene interactions are stronger than chloroform-chloroform and benzene-benzene interactions.


1

The following is based on comparing retention indices, using two main sources: Practical retention index models of OV-101, DB-1, DB-5, and DB-Wax for flavor and fragrance compounds, DOI: 10.1016/j.lwt.2007.07.007 Linear retention indices in gas chromatographic analysis: a review; DOI: 10.1002/ffj.1887 Difference in retention are due to differences in ...


1

I respectfully disagree with @Quip_Boy. If you want to separate compounds based on their vapor pressures, you can just carry out a distillation, which is also based on a gradient in temperatures along the column, whereas a capillary column used in GC is kept at the same temperature all the way in an oven. So there must be something else in the process. You ...


1

For GC, the most significant factor affecting separation resolution is differences in vapor pressures, boiling points if you will, between analytes. While column phase selection, oven temperature programming, detector type and temperature, and other factors will have an effect on the efficiency of separation, IMFs are not generally important for the ...


1

Maybe it would be better to discuss the question whether non-polar molecules can make hydrogen bonds using stable molecules as example, such as 1,2 ethanediol (ethylene glycol). On paper in the most stable conformation, ethylene glycol looks non-polar (2-fold rotational symmetry). However, if we compare its properties to those of ethanol (a polar molecule ...


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