Questions tagged [physical-organic-chemistry]

For questions about how organic molecules and reactions are investigated using physical experiments.

Filter by
Sorted by
Tagged with
1 vote
0 answers
36 views

What happens to polymers under high pressure?

What happens when you have polymers under high pressure? My very sketchy thoughts of polymers are that they can be thought of tangles of carbon chains surrounded by hydrogen, but that some polymers ...
user avatar
  • 119
0 votes
0 answers
17 views

How significant is the effect of pi stacking on substituent bond dissociation in an enzyme?

Let there be a system of phenylalanine in a T-shaped pi-stacking configuration with a tyrosine. Both are part of a longer peptide (~40 amino acid separation in the chain). In this system, an oxonium-&...
user avatar
  • 49
1 vote
1 answer
83 views

Why doesn't tetrachloromethane react with aqueous sodium hydroxide under reflux?

$\ce{CCl4}$ does not react with hydroxide nucleophile whereas $\ce{CH3Cl}$ does. I had initially thought that it was due to symmetrical geometry of $\ce{CCl4}$ and so the dipoles cancel out and the ...
user avatar
2 votes
0 answers
30 views

Why we use various layers in OLED (ETL,EIL,HTL,HIL)? How they increase efficiency OLED device? [closed]

Currently, I am studying the working of OLED devices! The device can work with just three layers which are Anode, Cathode and Emission layers. I know the fact that the work function is an important ...
user avatar
-2 votes
1 answer
71 views

Boiling and melting points of hydrocarbons [closed]

What happens while boiling and melting hydrocarbons? Which bonds are broken? When we compare the boiling point (b.p.) and melting point (m.p.) of certain hydrocarbons the order is inverted. For ...
user avatar
6 votes
1 answer
389 views

Fluorine detection in organic compounds

Many of you will know why I am asking this question. There is a lot of attention recently to the dangers of the so called Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS). In essence organic ...
user avatar
-3 votes
1 answer
54 views

Why do we need Equilibrium Constant as well as Acid Disocciation Constant? [closed]

I did the experiment to find out the dissociation constant of a weak acid using Henderson equation. However, after going through the theoretical part of the experiment, I am wondering why we need two ...
user avatar
  • 297
-1 votes
1 answer
37 views

Why in calculating 25 mM of Tris HCl the answer in gram is automatically refer to the gram in 1000 ml [closed]

In the lab class,my teacher told me that the answer i get in grams is automatically the grams in 1000 ml. Why is it possible without we doing anything the grams i get automatically the grams in 1000 ...
user avatar
0 votes
1 answer
41 views

How does addition of side chains affect solubility and processibility of polyphenylene vinylene?

I am studying electrical engineering and physics. In a recent lecture I was told the $\ce{OC1C10}\text{-PPV}$ molecule has the chains added to the oxygen atom down below because it allows for ...
user avatar
3 votes
1 answer
135 views

Comparing rates of substitution reactions

The following question was asked in an exam I gave recently Compare the overall rates of the following substitution reactions $$\ce{CH3Cl ->[OH-][Weak P.A.S] CH3OH}$$ $$\ce{CH3CH2Cl ->[OH-][ ...
user avatar
  • 1,345
2 votes
0 answers
104 views

Why is the enthalpy of formation of 2,2-dimethylpentane larger than that of 2,2,3-trimethylbutane?

Firstly, it is commonly known and taught that branched alkanes are more stable than linear ones, and so have larger enthalpies of formation. But why is that the case? Are there some steric ...
user avatar
  • 37
8 votes
1 answer
153 views

Out of tropolone and tropone, which is more soluble in water?

According to me tropolone has intramolecular H-bonding, so extent of H-bonding with water will decrease and thus, will be less soluble. Tropone (Cyclohepta-2,4,6-trien-1-one): Tropolone (2-...
user avatar
  • 89
1 vote
0 answers
23 views

How do electrostatic effects effect facial selectivity in addition to cyclic oxo-carbeniums?

I was reviewing Dave Evans' notes for stereochemistry of C=X electrophile additions, and found this slide detailing differences in additions to cyclic oxo-carbenium electrophiles, but I don't ...
user avatar
0 votes
0 answers
46 views

Why does Red Phosphorus react so violently with an oxidizer like Potassium Chlorate?

In Armstrong's Mixture, mixing those two chemicals results in a friction sensitive explosive which produces a loud bang. According to wikipedia, it is made by adding a strong oxidizer to red ...
user avatar
2 votes
0 answers
30 views

What kinetic model does the hydrogenation reaction of dibenzyltoluene follow?

So during the course of my research, I've read countless papers related to the hydrogenation of dibenzyltoluenen and the dehydrogenation of perhydro-dibenzyltoluene. Now what I've noticed, is the fact ...
user avatar
  • 113
4 votes
0 answers
28 views

Normalising Kinetic Isotope Effect Per Deuterium Atom

I've synthesised a protic and deuterated version of a specific molecule where there are two deuterium atoms in the latter. I then go about and measure the kinetic isotope effect (KIE) for a reaction ...
user avatar
  • 397
2 votes
1 answer
49 views

Small scale gas-to-liquids via Fischer–Tropsch — is it even possible?

I'm really interested in the Fischer–Tropsch gas-to-liquids (GTL) process. A lot of people are using wood or other biomass feedstock to make syngas on small scales (farms, shops, etc.). Practically, ...
user avatar
2 votes
0 answers
92 views

pKa of acetic acid in pure NH3?

Acetic acid completely dissociates in liquid ammonia and I would like to know the $\mathrm{p}K_\mathrm{a}$ value for the acid in that solvent. Can anybody point me to a reference?
user avatar
2 votes
0 answers
182 views

Comparison of boiling points of para-derivatives of phenol

The boiling points of four para-derivatives of phenol are: How can we compare the boiling points of p-nitrophenol and p-aminophenol? Apart from the hydroxyl group, p-nitrophenol has two oxygen atoms ...
user avatar
  • 1,147
2 votes
3 answers
356 views

salt hydrolysis and pH calculations

I am a high school student and I am very confused in salt hydrolysis My confusion is that: when we talk of hydrolysis of salt of weak base and weak acid, we internally assume the degree of hydrolysis ...
user avatar
2 votes
0 answers
48 views

Origin of the NMR shielding

In a paramgnetic material the induced dipole moment of atoms or (molecules) of the material aligns with the external field. I can understand this by Zeeman splitting. A term symbol splits into states ...
user avatar
  • 742
6 votes
1 answer
1k views

Aspirin Hydrolysis at pH 2

Conducting an experiment, I found that very little salicylic acid was evolved performing hydrolysis at $\mathrm{pH \ 2}$ and at $\pu{45 ^\circ C}$. In fact, far more salicylic acid was evolved at $\...
user avatar
  • 397
1 vote
0 answers
41 views

Would the initial step of this mechanism be exothermic or endothermic? (Protonation)

My understanding is that since an O-H bond is being formed, the protonation step must be exothermic because energy is released upon bond formation. However, if I were to draw an energy/reaction ...
user avatar
3 votes
1 answer
564 views

Why is the boiling point of sugarcane juice lower than the boiling point of water?

As the boiling point is a colligative property, one would expect that the boiling point of sugarcane juice should be higher than pure water because Sugarcane juice contains water (75–85%), non-...
user avatar
5 votes
0 answers
66 views

Does π values vary in Hansch-Fujita equations for a given substituent?

I was reading about Hansch-Fujita equations from Hansch-Fujita paramaters and observed that the $π$ values of substituents (analogous to Hammet $σ$ values) change according to the specific environment ...
user avatar
  • 742
3 votes
0 answers
100 views

Can cycloaddition reactions be antarafacial?

Cycloaddition reactions of the form [4+2] and [2+2] are always suprafacial, as the geometry is too constrained to allow for antarafacial interaction between the FMO's. However, for cycloaddition of ...
user avatar
5 votes
0 answers
98 views

How do bonds rotate in pericyclic reactions?

In Pericyclic reactions, it is shown that the terminal bonds rotate (conrotation or disrotation) to allow for allignment of the FMO's, thereby forming the sigma bond However, a detail that most of my ...
user avatar
0 votes
1 answer
119 views

What's the least common element in the universe? [closed]

What's the least common element in the universe? And what is its frequency measured in Hertz?
user avatar
  • 21
1 vote
2 answers
52 views

Organic-catalysis microwaves [closed]

When we perform a organic reaction without any addtional catalyst except that the reaction is carried out under microwave condition we can accelerate this reaction in comparison with one under heating ...
user avatar
2 votes
1 answer
47 views

Carboxyllic acid Test

I'm currently in high school doing a project in chemistry. So I had to make a project where concepts from physical chemistry will be used alongside organic chemistry. After going through my book I ...
user avatar
  • 21
-1 votes
1 answer
273 views

Will a salt dissociate completely in water to give free ions?

I was reading salt hydrolysis of a salt made from strong acid and weak base. I came across the hydrolysis of $\ce{NH_4Cl}$. These reactions were mentioned $$\ce{NH_4Cl + H_2O<=>NH_3 + HCl \tag{...
user avatar
  • 480
0 votes
2 answers
240 views

Fermentation of glucose

I have trouble understanding as to what the last part of the increase in liquid level means. I believe this is the foam formed after the fermentation? I am calculating for the pressure but I have ...
user avatar
  • 31
1 vote
0 answers
18 views

What is the influence of citrate on PEG-modified polyacrylamide hydrogels?

I've been having a puzzle explaining the experimental results with the citrate anions and PEG modified polyacrylamide: According to the experimental data there is a hydrogel swelling whenever citrate ...
user avatar
3 votes
1 answer
49 views

Vapors of Aqueous solutions

I'm dealing with a common photoresist developer TMAH (tetramethylammonium hydroxide) and attempting to design a vapor sensor for a sealed chamber. Now I havent been able to confirm what exactly is ...
user avatar
  • 41
1 vote
0 answers
52 views

Primary kinetic isotope effect

Why does the transition state in both protonated and deuterated molecules have the same energy? My textbook assumes that during transitional state the isotopic bond is half-broken or on its way to ...
user avatar
  • 545
4 votes
1 answer
339 views

Overlap integrals in Hückel theory

In Hückel theory we are only interested in π systems, where $\mathrm p_z$ orbitals overlap. One of the approximations in Hückel theory is that the overlapping $\mathrm p_z$ orbitals are orthonormal: $...
user avatar
  • 302
4 votes
1 answer
628 views

How do we obtain the π molecular orbitals for allene via Hückel theory?

For a conjugated system, for instance 1,3-butadiene, we can try to obtain the π molecular orbital energies and wavefunctions via Hückel theory. In our given molecule, there are 4 interacting Pz ...
user avatar
  • 302
0 votes
0 answers
31 views

A question about potential difference across a membrane

Membrane potential of living cells arising from the difference of concentration of ions on both sides of the membrane, but why didn't someone use selective polymers as AEM (Anion Exchange Membrane) ...
user avatar
  • 545
4 votes
1 answer
100 views

What exchange timescales are needed to cause decoupling in NMR?

I'll try to explain the source of my confusion as clear as possible: (*) The methyl protons in toluene are decoupled because the C-C bond between the methyl group and benzene allows very fast ...
user avatar
  • 461
3 votes
0 answers
191 views

Why does Larmor precession occur in NMR?

Larmor precession is the phenomenon that in NMR the spin (and by default also the magnetic dipole moment) of protons does not line up with the applied magnetic field but rather precesses around this ...
user avatar
  • 461
0 votes
0 answers
37 views

What is the justification for using the Marcus rate equation to model charge transport in organic semiconductors?

I am trying to understand the history of how Marcus theory moved from describing electron exchange reactions in aqueous ionic solutions to also being applied to describe transport in organic ...
user avatar
9 votes
1 answer
561 views

What can we say about the dipole moment of terephthalic acid?

The dipole moment of quinol is not zero because it can exist in two different energetically favourable conformations. The weighted average is calculated to arrive a dipole moment of 1.6 D. According ...
user avatar
  • 1,147
2 votes
2 answers
576 views

Why does the dipole moment of molecules go from positive to negative? [duplicate]

In physics the dipole moment is said to go from the negative to the positive pole, check for instance https://en.wikipedia.org/wiki/Electric_dipole_moment (Elementary definition). This makes sense ...
user avatar
  • 461
3 votes
1 answer
2k views

Ratio of uncharged to charged side chains [closed]

The $\mathrm{p}K_\mathrm{a}$ of the side chain imidazole group of histidine is $6.0.$ What is the ratio of uncharged to charged side chains at $\mathrm{pH}~7?$ Here's my attempt to the solution: $$7 ...
user avatar
  • 41
1 vote
0 answers
52 views

Volatility comparison for isomers of phthalic acid

All the atoms of these compounds are in a plane. o-phthalic acid can show extensive intra-molecular hydrogen bonding as well as inter-molecular hydrogen bonding. m-phthalic acid can show intra-...
user avatar
  • 1,147
1 vote
0 answers
36 views

Enantiomeric excess catalysed

Enantiomeric excess is defined as $$ee = \frac{[R]-[S]}{[R]+[S]}$$ I found this problem in an IChO paper: "When using the enantiomerically pure (BINOL)Al(OiPr) as a catalyst for reduction of ...
user avatar
0 votes
1 answer
108 views

Why has nature evolved to put a porphyrin (i.e. chlorophyll) as the chromophore in a leaf? [closed]

I'm stumped by this question: Why has nature evolved to put a porphyrin (i.e. chlorophyll) as the chromophore in a leaf? I've thought that it might have something to do with how sun emits light ...
user avatar
4 votes
2 answers
127 views

Enzyme Kinetics

How come enzymes with a lower $K_\mathrm{m}$ are more easily saturated with substrate than an enzyme with higher $K_\mathrm{m}?$ Is it because enzymes with higher $K_\mathrm{m}$ are able to bind ...
user avatar
1 vote
1 answer
130 views

Why does the reduction of Dichromate to Chromium 2 need an acid? [closed]

The Ecell shows that Zn is enough. Then why, are both of them required? Also, can I use any acid ? Or only HCl + H2SO4
user avatar
  • 7
1 vote
1 answer
948 views

Why do weak acids like ethanol not act as a strong base in water?

In water, ethanol has a $\mathrm{p}K_\mathrm{a} = 15.9$ which means that its $\mathrm{p}K_\mathrm{b}$ is $-1.9$. Which implies that all weak acids in water are in fact strong bases. But this is not ...
user avatar