Questions tagged [reaction-mechanism]

The detailed (and as complete as possible) description of plausible or observable pathways leading from reactants to products of a chemical process. This tag should be applied to questions about these processes. It may be applied to hypothetical and/or proposed mechanisms.

Filter by
Sorted by
Tagged with
12
votes
1answer
18k views

Mechanism of carboxylic acid and amide dehydration with phosphorus pentoxide

Dehydration of carboxylic acids with phosphorus pentoxide ($\ce{P2O5}$) yields acid anhydrides, and in a similar reaction, amides dehydrated with phosphorus pentoxide yield cyanides. Can an arrow ...
12
votes
1answer
7k views

Why would sulfuric acid turn gray/black?

About 2 years ago I purchased 2 liters of 98% concentrated sulfuric acid. It's in a standard poly bottle with leakproof lids, and originally was clear. Recently I noticed the acids have turned a dark ...
12
votes
3answers
3k views

Is water a better nucleophile than bromide?

I am a student of biochemistry. My organic chemistry professor was giving a lecture and he talked about halohydrin formation reactions. At one point, he said that "water attacks instead of bromide ...
12
votes
1answer
391 views

Rearrangement with sodium iodide (ring opening)

I'm not able to figure out the mechanism for this reaction. I don't see how sodium iodide in acetone could lead to rearrangement, and surprisingly ring opening! What is this reaction called, if it ...
12
votes
1answer
541 views

What are the key chemical characteristics that determine the octane rating of fuel?

The octane rating of petrol (gasoline) is a measure of the how much compression a fuel air mixture can have before detonating (which in petrol engines is a bad thing as you want the mix to combust ...
12
votes
3answers
738 views

Why is the rate of reaction of polar EAS favored by inductive effects and the rate of less polar EAS reactions through hyperconjugation?

1. Reactions involving strong electrophiles (nitration) are said to be governed by Inductive effects thus the order of nitration is D>C>...
12
votes
1answer
392 views

What's the reaction type of the Hydrogen shift?

Rearrangement of cycloheptatrienyl carbene yields heptafulvene via a hydrogen shift. I see that the reaction is favorable because there is a conjugative effect with the $\pi$ system of the ring in ...
12
votes
1answer
3k views

Ipso substitution and its rules

I was taught that the following reaction happens: It is called the "ipso-substitution". My professor had told me that it occurs in the case of $\ce{-SO3H}$ and $\ce{-COOH}$. But he had ended the ...
12
votes
1answer
447 views

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 ...
11
votes
2answers
55k views

How does propylene glycol/glycerin form formaldehyde/acetaldehyde when vaporized?

So apparently, e-cigarettes produce formaldehyde/acetaldehyde because they vaporize propylene glycol/glycerin. What is the chemical reaction through which propylene glycol/glycerin forms formaldehyde/...
11
votes
1answer
45k views

What is the mechanism for oxidation of ketones by the Popoff's rule?

Ketones are relatively much harder to oxidise, but they do undergo oxidation reactions at extreme temperatures. Our teacher also told us about Popoff's rule which states that, on oxidation of ...
11
votes
2answers
865 views

When 2-pentene reacts with HBr, what will be the major product?

If we consider the first step (formation of carbocation by the attack of the proton). A couple of textbooks I referred say that when the substituents on the $\ce{C=C}$ are different, the direction of ...
11
votes
3answers
4k views

How is it that the equilibrium constant does not depend on the mechanism?

For a reaction of the form $$\ce{aA + bB <=> cC + dD}$$ the equilibrium constant is $$K_c=\frac{[\ce{C}]^c[\ce{D}]^d}{[\ce{A}]^a[\ce{B}]^b}$$ regardless of the mechanism of the reaction. ...
11
votes
4answers
2k views

Does radioactivity affect chemical reactions?

Do compounds of radioactive elements show a different behaviour? What happens when the radioactive part of the given compound decays? e.g. Radium chloride; what happens to it when radium decays?
11
votes
1answer
196 views

Mechanism of radical cyclisation to form hydroazulene core

Recent studies on radical-induced cyclisation reactions have led to a simple, one-step method for the preparation of hydroazulenes from appropriately substituted cyclopentanone precursors. Treatment ...
11
votes
1answer
2k views

Purpose of ammine in Tollens' reagent

In this previous question the mechanism for the reaction of Tollens' reagent was outlined. As I understand it the oxidising agent in Tollens' is the diamminesilver(I) complex $\ce{[Ag(NH3)2]+}$ but ...
11
votes
1answer
842 views

Chemical equation that can be balanced in infinite number of ways?

When I was studying for my chemistry test, I found an equation that illustrates how to get water gas (carbon monoxide + hydrogen) out of methane. It is stated like this: $$\begin{align}\ce{2CH4 + CO2 +...
11
votes
2answers
819 views

N-fluorosuccinimide: any scope?

All halogen derivatives (except fluorine) of succinimide exist and are used in various chemical processes. What makes N-fluorosuccinimde difficult to prepare? Still chemists have not been able to ...
11
votes
1answer
10k views

Mechanism for chloromethylation of benzene with formaldehyde and HCl

What is the mechanism of the above reaction? I have thought of one possibility: Would this work? How exactly is the chlorine installed on the alkyl chain?
11
votes
1answer
178 views

Models for diastereoselectivity in nitronate additions

In the scheme below (taken from the referenced Chem. Eur. J. paper on the synthesis of Tamiflu), there is a step in which a nitronate anion (the anion derived from 5) is added into an electrophile 6, ...
11
votes
1answer
502 views

Wittig versus Corey–Chaykovsky reaction

The Wittig and Corey–Chaykovsky reaction both involve an ylid, phosphonium ylid in the former versus a sulfonium ylid in the latter, attacking a carbonyl compound. In the Wittig reaction, a ...
11
votes
2answers
3k views

Why is the Still-Gennari reaction Z-selective?

Why is the Still-Gennari reaction Z-selective? I guess dipole interactions have the biggest influence here. They somehow destabilize the reversion of the oxaposhpetane to the betaine and prevents ...
11
votes
1answer
305 views

Formamide and Hoffmann Bromamide Reaction

I encountered a problem to identify the compound which does not give Hoffmann bromamide degradation reaction. One of the options was formamide, and it was given as the answer. Why can't formamide ...
11
votes
1answer
175 views

Finding chair and boat transition states during ring-forming reactions

Reactions that form 6 membered rings most commonly go via either boat or chair transition states but the products themselves do not necessarily adopt the same conformation as the TS. I'm attempting ...
11
votes
1answer
926 views

In the Favorskii rearrangement, why doesn't the base grab the alpha hydrogen of the carbon bearing the halogen?

In the Favorskii rearrangement, the base (like hydroxide) always abstracts the alpha hydrogen of the carbon not bearing the halogen. But to me the hydrogens on the carbon directly connected to the ...
11
votes
1answer
2k views

In the elementary steps of a reaction, why do we assume that the coefficients of a reactant correspond to its order?

Recently, I was taught that the coefficients of the reactants in an elementary step of a reaction indicates that reactant's order. Why is this the case? I thought that the order of a reactant was not ...
11
votes
1answer
5k views

Crossed Cannizzaro products

I have understood the basic mechanism of cannizzaro reaction. But I am unable to understand the products formed in case of a crossed Cannizzaro reaction. Suppose Benzaldehyde and Formaldehyde are ...
11
votes
1answer
1k views

Resonance in carbocation derived from allenes

During a reaction if addition on one of the $\pi$ bonds of an allene (containing even number of $\pi$ bonds like $\ce {H2C=C=CH2}$) takes place then a carbocation is formed. To decide the position of ...
11
votes
3answers
4k views

Internal Cannizzaro reaction of phenylglyoxal

Phenylglyoxal $(\ce{PhCOCHO})$ can undergo both internal Cannizzaro reaction and between two molecules. The internal Cannizzaro reaction is like this: Which reaction will be preferred? Internal ...
11
votes
3answers
40k views

Gattermann-Koch Reaction with Phenol Substrates

The Gattermann-Koch Reaction involves the formation of an aryl aldehyde using carbon monoxide and hydrochloric acid as reactants. The reaction is catalyzed by aluminium trichloride in the presence of ...
11
votes
1answer
2k views

Why does treatment of a geminal dihalide with sodium amide lead to an alkyne and not an allene?

I've come across the following problem in Klein's Organic Chemistry, 2nd edition: However, I'm a little bit confused about why the terminal alkyne is produced. I believe that an allene should be ...
11
votes
1answer
1k views

Birch reduction of anisole

Hepworth, Waring and Waring (2002) mentions that: In general, electron-withdrawing substituents make the arene more susceptible to reduction, while the opposite applies for electron-donating ...
11
votes
1answer
1k views

Product of Friedel-Crafts cyclisation of (3-methylpent-4-en-1-yl)benzene

My proposed mechanism and final product is: But the book says the answer is: I know that a 6 membered ring is more stable than a 5 membered ring so I made the product with the 6 membered ring (...
11
votes
1answer
5k views

What is the role of NaHSO3 in syn diol formation from alkenes with OsO4?

All I have found on this is that NaHSO3 reduces partially the osmate ester, so breaks off Os and leaves a syn diol. Is it possible to show this step with arrows showing the process of electron ...
11
votes
1answer
509 views

Benzyne formation with Grignard reagents

Nucleophilic substitution through an elimination-addition mechanism (involving benzyne formation) occurs with a strong base. $\ce{NH2-}$ can show this reaction. Can Grignard reagents $\ce{RMgX}$, ...
11
votes
1answer
4k views

Why do alpha-hydroxy ketones respond positively to Tollens', Fehling's, Benedict's, Schiff's and HgCl2 tests?

I learnt from a certain textbook that aldehydes and formic acid respond positively to Tollens', Fehling's, Benedict's, Schiff's and HgCl2 tests. However, in another textbook I read that even alpha-...
10
votes
3answers
2k views

Why is more of a catalyst added, when it is not consumed?

… catalysis, the acceleration of chemical reactions by substances not consumed in the reactions themselves—substances known as catalysts. (Source) Now as I’ve understood, to keep a reaction going, ...
10
votes
2answers
1k views

Prediction of products in reaction of dicarbonyl with alpha-haloketone

Following is the question that was asked in my exam. a,b,c,d are the various options, one of which is the answer. I am familiar with the Reformatsky reaction, Aldol condensation, Knoevenagel's ...
10
votes
2answers
11k views

Chlorination by SOCl2 vs SO2Cl2

My textbook mentions that chlorination of alkanes by $\ce{SO2Cl2}$ is preferred over $\ce{SOCl2}$, but I didn't understand why. Could someone explain which of the two reagents I should use in what ...
10
votes
2answers
3k views

How does copper reduce dilute nitric acid to nitric oxide and concentrated nitric acid to nitrogen dioxide?

Here are the 2 equations: \begin{align} \ce{3Cu + 2NO3- + 8H+ &<=> 3Cu^2+ + 2NO + 4H2O} & E &= 0.62~\mathrm{V}\\ \ce{3Cu + 2NO3- + 4H+ &<=> 3Cu^2+ + 2NO2 + 2H2O}& E &...
10
votes
2answers
638 views

Reaction between a carbene and n-pentane

Does the following reaction occur when n-pentane reacts with methylene or does it form some other simpler products due to the reactivity of the carbene? $\ce{CH3-(CH2)3-CH3 + :CH2-> CH3-(CH2)4-CH3}...
10
votes
2answers
4k views

Rate Constant Units and Eyring Equation

Rearranging the Eyring equation leads to the following: $$\Delta^\ddagger S^\circ = R \ln{\frac{k \times h}{{k_\text{B}}{T}}}+\frac{\Delta^\ddagger H^\circ}{T}$$ where $k$ is the rate constant, $h$ ...
10
votes
1answer
161 views

Are nucleophilic aromatic substitutions stepwise or concerted?

Recently, there has been a lot of discussion about nucleophilic aromatic substitution (SNAr) reactions apparently being concerted instead of stepwise (e.g. Krämer, K. Textbook aromatic substitution ...
10
votes
1answer
4k views

How does the HCl-KCl Buffer work?

I have just been studying the $\ce{HCl}$-$\ce{KCl}$ 'buffer', but there are still quite a few things I am uncertain about. I would appreciate any help in clearing up some questions I have. What I ...
10
votes
2answers
1k views

Ring expansion from a given cyclic carbocation

How will the cyclobutane ring behave in the case of cyclobutylmethylium (cyclobutylmethyl cation)? I initially thought there would be ring expansion to a five membered ring so that there may be less ...
10
votes
2answers
6k views

What are the products of the reaction of 1-methoxycyclohexene with dilute hydrochloric acid?

When 1-methoxycyclohexene is treated with dilute aqueous hydrochloric acid, methanol is produced along with another organic product. Identify this product. Explain why methoxycyclohexane is inert ...
10
votes
1answer
2k views

How does toluene react at higher temperatures and why?

Reaction of toluene at high temperatures gives us (o-m)toluene; whereas at normal conditions of electrophilic attack, it gives us (o-p) directing. Why does this happen at high temp although as methyl ...
10
votes
1answer
3k views

What happens when an alkylborane is treated with acetic acid?

In the hydroboration reactions of alkenes I've seen so far, they were always followed by oxidation with $\ce{H2O2/NaOH}$ (to yield alcohols). Today I found a peculiar reaction in which acetic acid-...
10
votes
1answer
3k views

Why is the reduction by sugars more efficient in basic solutions than in acidic ones?

Why is it said that reduction by sugars is much more efficient in basic media than in acidic media as in the following quote taken from Satyanaryana’s Biochemistry, 4th edition page 16? In the ...
10
votes
1answer
20k views

Mechanism for formation of amide by reaction of amine with ester

This is the mechanism given in my lecture handout: I have a problem with the third species along. Surely the negatively charged oxygen would protonate before the other oxygen would. Also, why does ...