Questions tagged [physical-organic-chemistry]

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

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2
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1answer
34 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, ...
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1answer
58 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?
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0answers
20 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 ...
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3answers
81 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 ...
2
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0answers
34 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 ...
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0answers
26 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 ...
3
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1answer
169 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-...
5
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0answers
20 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 ...
3
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0answers
41 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 ...
5
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0answers
78 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 ...
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1answer
75 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?
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2answers
45 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 ...
2
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1answer
35 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 ...
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1answer
56 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{...
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2answers
96 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 ...
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0answers
13 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 ...
3
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1answer
41 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 ...
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0answers
36 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 ...
4
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1answer
146 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: $...
4
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1answer
299 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 ...
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0answers
28 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) ...
4
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1answer
74 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 ...
3
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0answers
85 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 ...
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0answers
27 views

chitosan question [closed]

when chitosan is coated on the surface of iron oxide nanoparticles, are the amine groups of the chitosan pointed out?
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0answers
32 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 ...
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0answers
225 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 ...
2
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2answers
334 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 ...
2
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1answer
757 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 ...
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0answers
47 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-...
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0answers
27 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 ...
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1answer
86 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 ...
4
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2answers
58 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 ...
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1answer
83 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
1
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1answer
479 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 ...
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1answer
32 views

Alkene production by dehydrohalogenation [closed]

What is the difference in the reaction mechanism when alkyl halides are reacted with aq.koh and alcoholic koh along with products
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1answer
33 views

Zinc and copper [closed]

Is potential energy and ionisation energy are same? Plz explain with respect to zinc Why zinc is undergoing oxidation when combined with with zinc. copper in electrochemical series
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1answer
210 views

which one is the correct statement of “Law of definite proportion”? [closed]

according to my genius Teacher ' this law state that "the composition of a compound in terms of atoms (Not Mass) remains constant". His Proof: H2O and D2O are similar compounds (because H and D have ...
47
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6answers
9k views

Why does wood burn but not sugar?

Fundamentally, they're both carbohydrates, although the cellulose in wood is essentially polymerized glucose, which combined with its isomer fructose forms sucrose. So why does wood readily burn ...
4
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0answers
105 views

Number of configurations/states for electrons in orbitals

I'm performing complete active space calculations for the prediction of X-ray absorption L edge spectra. This involves an excitation from 2p orbitals to the 3d orbitals of the metal. For the ...
6
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2answers
894 views

How can isotope labelling be used to determine the mechanism of ether cleavage with hydrogen iodide?

When methyl tert-butyl ether (MTBE) is treated with one equivalent of hydrogen iodide, the ether C–O bond is cleaved. I read that if the oxygen in MTBE is isotopically labelled, it is possible to ...