Questions tagged [reaction-control]

Questions related to the chemical and physical influences that influence the rate and probability of chemical reactions. Not to be confused with [catalysis] or [reaction-mechanism].

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Why is −78 °C a magic temperature for organic reactions?

In many organic reactions that I have seen, running the reaction at $\mathrm{-78\ ^\circ C}$ seems to be quite a popular choice, but I've never seen any explanation for this. What makes this ...
ringo's user avatar
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27 votes
1 answer
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Addition of hydrogen bromide to 1,3-butadiene: thermodynamic and kinetic control

The reaction of one equivalent of hydrogen bromide with 1,3-butadiene gives different products at under different conditions:1 The addition of hydrogen chloride also gives rise to similar products.2 ...
orthocresol's user avatar
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26 votes
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Michael reaction or nucleophilic attack at the alpha carbon of an alpha-beta-unsaturated ketone?

What conditions promote a nucleophile to undergo the Michael reaction over the nucleophilic attack at the alpha carbon of the carbonyl group in an alpha-beta-unsaturated ketone? I'm looking for an ...
LanceLafontaine's user avatar
15 votes
3 answers
3k views

Does gravity affect the rate of a chemical reaction?

For example, on planets with lower gravity, would the rate of reactions be lower because the reactants are slower to mix with one another?
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14 votes
2 answers
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Thermodynamic and kinetic products - carbocation stability

The professor wants to know which is the thermodynamic product and which is the kinetic product. He says there are only two products - the two on the right that result from the resonance-stabilized ...
Dissenter's user avatar
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13 votes
1 answer
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Aza-enolates: why no reaction at N

My understanding is that aza-enolates have an advantage over enamines in enolate-type alkylations because the reaction at N is less likely. As a result, unactivated electrophiles can be used (i.e. ...
GingerBadger's user avatar
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12 votes
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How does heptafluoropropane suppress fire?

How does heptafluoropropane suppress fire? It says here that it does so by "inhibiting the chain reaction." What does that mean specifically? Does $\ce{O2}$ attach itself to the heptafluoropropane?...
Al Lelopath's user avatar
12 votes
1 answer
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Why does water favour nucleophilic substitution over elimination?

The two broad ways a halogen can leave a haloalkane are nucleophilic substitution and elimination reactions. I was told that elimination reactions (that form a double bond as a $H^+$ is also removed) ...
Meow's user avatar
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Noyori hydrogenation and the Curtin–Hammett principle

My question is relating to how the Curtin–Hammett principle applies to homogeneous hydrogenation using chiral ligands. Figure 0: An example of a quadrant diagram used as a mnemonic to predict the ...
NotEvans.'s user avatar
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11 votes
2 answers
347 views

Chemical oscillators that behave like a double pendulum

Oscillating chemical reactions such as BZ-reaction or chemical clock typically result in sequential systematic changes, most notable of which is arguably coloring. Though underlying mechanism can be ...
andselisk's user avatar
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11 votes
1 answer
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What makes a compound a dehydrating agent?

When a carboxylic acid with low molecular weight is heated with $\ce{P2O5}$ we get the corresponding anhydride. My book says that this reaction happens with dehydrating agents such as $\ce{P2O5}$. I ...
Karan Singh's user avatar
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11 votes
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Role of pH in azo C-coupling reaction, continued

In the question, "What is the role of pH in azo coupling reaction of diazonium with phenol and aniline?" asked by @DhrubaBanerjee and answered by @Klaus-DieterWarzecha, I find several ends ...
William R. Ebenezer's user avatar
10 votes
2 answers
111k views

What are the differences between diesel and unleaded gasoline?

I am curious about the flammability of diesel fuel and its properties, as I don't deal with it on a regular basis (at all). In particular, I want to know how the fuel works when powering a diesel ...
Malachi's user avatar
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10 votes
4 answers
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Why do we use Δ to mean heating?

To express heating, we usually use $\Delta$ over reaction arrows like \begin{align} \ce{CaCO3 ->[\Delta] CaO +CO2}. \end{align} Why do we use $\Delta$ to mean heating during chemical reactions? I ...
Sakai's user avatar
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9 votes
4 answers
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Why should the temperature be maintained at 0–5 °C in a diazotisation?

I know that in a diazotisation reaction, the temperature should be carefully maintained within the range of 0–5 °C by use of an ice bath. Why is this so? How does the temperature affect the stability ...
Karthi Keyan's user avatar
9 votes
1 answer
1k views

Does (chloromethoxy)ethane react in a bimolecular or monomolecular mechanism?

It is known that (chloromethoxy)ethane forms stable carbonium ions based on Nobel prize Chemist George Olah research Olah's method. This would indicate that (chloromethoxy)ethane reacts through $\...
Mikael Jumppanen's user avatar
8 votes
3 answers
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Why do we need sulfuric acid in creating alkyl bromide and not in creating alkyl iodide from alcohol and hydrogen halide?

i) $\ce{R-CH_2-OH + HBr ->[H_2SO_4] R-CH_2-Br + H_2O}$ ii) $\ce{R-CH_2-OH + HI -> R-CH_2-I + H_2O}$ What role does sulfuric acid play in the first reaction? Why are we not using it in the ...
Tiash's user avatar
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8 votes
1 answer
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What visual observations can confirm that a reactant is the limiting reagent?

I have this lab question for the lab called Copper Collection Stoichiometry, where we choose an amount of the limiting reagent (iron) for a reaction between copper (II) sulfate and iron. We are to ...
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8 votes
1 answer
8k views

Relationship between surface area of electrode and reaction rate of hydrogen in fuel cells

I am looking at the effects of increasing the surface area of which the flowing hydrogen fuel is in contact with the anode in a fuel cell. At the anode the hydrogen is catalytically split into ...
Blue7's user avatar
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7 votes
2 answers
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Does high pressure reverse reaction between zinc and sulfuric acid?

When zinc is added to sulfuric acid, it undergoes a chemical reaction that generates hydrogen gas and zinc sulfate. Can this reaction be reversed by applying pressure to the products converting them ...
Dr Potato's user avatar
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1 answer
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Python package for modelling chemical reactions

I'm looking for a package that is compatible with Python 3 and can actually do work with reactions along with, for instance, referencing values. Ideally, it should also not be a package that will take ...
auden's user avatar
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7 votes
1 answer
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How does the solvent determine whether mono- or tribromination of phenol occurs?

In phenol, the $-\ce{OH}$ group activates the benzene ring towards electrophilic substitution. But why is it that the electrophilic bromination of phenol gives trisubstitution (forming 2,4,6-...
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7 votes
0 answers
108 views

How well will molten iron chrysolite (fayalite) react with hydrogen?

The equation balances nicely, but would the reaction tend to proceed this way? What temperature and time would be needed? $\ce{Fe2SiO4 + 2H2 -> 2H2O + 2Fe + SiO2}$ There is no problem with ...
kim holder's user avatar
6 votes
1 answer
2k views

Formation of Aniline from Chlorobenzene

My textbook says: When chlorobenzene is treated with aqueous ammonia at 473K under a pressure of 60 atmospheres in presence of cuprous oxide or cuprous chloride, aniline is formed. Notice the ...
Nilabja's user avatar
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6 votes
1 answer
878 views

Why does sulfonation of alcohols even work?

I am now near the end of organic chemistry 2, and I'm trying to understand the patterns of reactions so that I can predict them rather than brute force memorizing all of them. Looking at the ...
Abid Rizvi's user avatar
6 votes
1 answer
1k views

Why does addition polymerisation of high density poly(ethene) use low temperature and pressure?

Logically thinking, I thought that it would be high pressure and high temperature that would create high density poly(ethene)... However, that's not the case. Is it because of the catalyst? Why is the ...
YH Kang's user avatar
  • 101
6 votes
1 answer
272 views

Decarboxylation of THCA during CO2 Extraction of Cannabis

We have a strange problem. We are performing CO2 extraction on cannabis and we are seeing considerable decarboxylation of THCA to THC. We have high quality temperature sensors at the heat exchangers, ...
oll67c's user avatar
  • 61
6 votes
1 answer
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How to inhibit Mn2+ autocatalysis in the oxalate-permanganate reaction?

It is well known that permanganate in acidic solution can oxidize oxalate ions (or oxalic acid). The reaction produces $\ce{Mn^2+}$, which catalyzes this very reaction. $$\ce{2MnO4^- + 16H^+ + 5C2O4^...
eflaschuk's user avatar
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0 answers
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Temperature control and side reactions in PPAA (T3P) couplings

In a lot of procedures for amide couplings (acid + amine) using PPAA, the coupling agent is added to a cooled solution of the acid, amine, and a non-nucleophilic base such as DIPEA. This is done even ...
NotEvans.'s user avatar
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5 votes
1 answer
32k views

Prove that a 10-Degree Temperature Increase Doubles the Rate Constant (k), when the Activation Energy is Approximately 50 kJ/mol

I read that increasing the temperature by $10~^\circ\mathrm C$ will double the rate constant ($k$), when the activation energy for the reaction is relatively close to $50~\mathrm{kJ/mol}$. However, ...
Sam202's user avatar
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5 votes
1 answer
318 views

A chamber to control concentration of a vapor: Is there a name for this equipment?

Mechanical engineer here so please excuse me if my question seems dumb to you! I want to have a chamber $(\approx 40 \times 30 \times \pu{30 cm})$ to control concentration $(\pu{ppm})$ of a flammable ...
Foad's user avatar
  • 197
5 votes
2 answers
2k views

Thermodynamic vs kinetic reaction control with radical substitution

Doing a revision for a chemistry class test tomorrow, I stumbled upon thermodynamic and kinetic reaction control in the context of radical substitution. Here, my chemistry teacher said, that ...
Tacticus's user avatar
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5 votes
2 answers
5k views

How does pH affect the degradation of ascorbic acid (vitamin C)?

I know that vitamin C degrades over time (as I understand through oxidation). However, I am having trouble understanding how changing the pH of the solution in which the vitamin C is affects the rate ...
Flyn Hutchison's user avatar
5 votes
0 answers
54 views

Increasing C-alkoxycarbonylation of enolates

I am working with N-tosyl-2-piperidone and attempts to use the lithium enolate of this compound to perform an nucleophilic acyl substitution reaction on an several chloroformate esters in THF has lead ...
SendersReagent's user avatar
5 votes
0 answers
153 views

Is there a way to force C-protonation of an enolate?

In another question, I mentioned that O-protonation of an enolate followed by tautomerization may lead to increased amounts of the thermodynamic product over the kinetic product (when those are ...
SendersReagent's user avatar
4 votes
3 answers
2k views

Why do some reactions require specific pressures to happen?

For example, carbon monoxide reacts with hydrogen to synthesize methanol in the presence of some catalysts, but the pressure needs to be $\pu{50 atm}$ and the temperature needs to be $\pu{523 K}$. ...
FinnTheHuman's user avatar
4 votes
1 answer
733 views

Why does phenolphthalein form in this reaction?

This reaction (http://orgsyn.org/demo.aspx?prep=CV1P0476) gives quinizarin as the major product in about 70% yield. However, when the same reaction is conducted with phenol insteas of p-chlorophenol, ...
FusRoDah's user avatar
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4 votes
4 answers
499 views

how to mathematically predict reaction results

I've been trying to computationally achieve the following (I have no lab, I'm 14 years old, and I want to make a Minecraft mod to teach real Chemistry): I want to mathematically predict the range of ...
FinnTheHuman's user avatar
4 votes
2 answers
11k views

Relationship between Gibbs free energy, enthalpy, entropy and rate of reactions

I'm having a little trouble constructing the bigger picture of chemical reactions. From the collision theory we know that molecules react if: 1) they collide 2) they collide bearing a sufficient ...
Cath L's user avatar
  • 111
4 votes
2 answers
3k views

Half life of Nitrofurantoin

Both wikipedia and Toxnet list the half-life of Nitrofurantoin as 20-60 minutes in the blood plasma. Can anyone explain how this is so short, especially for an antibiotic, and how it still has time to ...
Noah P's user avatar
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4 votes
1 answer
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E2 Reactions in Cyclic Structures

In my textbook, the percentages of anti-eliminations are given which are quite contrary to expectations. The reason is also not given quite clearly. Why does the preference for anti-periplanarity ...
Ayushmaan's user avatar
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4 votes
2 answers
1k views

Why does the Birch reaction not yield fully saturated products?

Why isn't benzene reduced all the way down to cyclohexane when performing a Birch reaction? (Why is it not reduced further?) Similarly for the reaction with sodium dissolved in liquid ammonia, why ...
hanna's user avatar
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4 votes
0 answers
116 views

CuAAC "Click" reaction giving inconsistent results

I apologize in advance for the large amount of text and thank all those who take the time to read it. The "Click" reaction after Fokin and Sharpless is known to achieve high yields without long ...
Sam's user avatar
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4 votes
1 answer
323 views

Which reaction rate formula is suited for diatomic molecules in a plasma?

I am an experimental physicist, so I unfortunately do not know much about chemistry except the basics. For my current study, I am investigating diatomic molecule formation in plasma. These diatomic ...
PoorYorick's user avatar
3 votes
3 answers
626 views

Can we make chemical bonds using light, instead of breaking them?

I am trying to bridge a conceptual understanding of how light affects both breaking and forming bonds. When bonds are broken, energy is absorbed (endothermic process). Conversely, when bonds are made, ...
Qubit's user avatar
  • 147
3 votes
3 answers
634 views

Why do some reactions need to be maintained at a particular temperature for prolonged periods of time?

Some reactions require that temperatures of 70–100 °C to be maintained for periods of time as long as 24 hours. Why is this so?
Zwolf's user avatar
  • 143
3 votes
2 answers
3k views

Thermodynamic versus kinetic reactions

In a lecture, teacher said "Nucleophilicity is about 'kinetic', and basicity is about 'thermodynamic'" but I saw the picture below from another source. Here, both pathways start with an acid/base ...
NK Yu's user avatar
  • 651
3 votes
2 answers
2k views

Mechanism of Halogenation of Alkene

In the above reaction, we use a non-polar compound (such as CCl$_4$) as a solvent. Then, why does the Br$_2$ polarise on attack by the alkene, even though a non-polar solvent does not encourage ...
Ayushmaan's user avatar
  • 1,132
3 votes
3 answers
1k views

Hydrogen reactions with catalysts

I have a question about reactions involving hydrogen using catalysts. I'm a layman, so forgive me if my questions seem elementary. Reacting hydrogen plus oxygen and a flame reacts, unleashing energy (...
RobA's user avatar
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3 votes
2 answers
2k views

Does pressure affect non-gaseous reactions?

Pressure holds a great significance when it comes to reactions involving gaseous species. Changing pressure can affect the kinetics and even mechanisms of such reactions. However, does pressure hold ...
Tabish Mir's user avatar
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