14 votes
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Why does boron add to the less substituted carbon in the hydroboration of an alkene?

For the hydroboration of isobutene there is a steric aspect: And though sterics may play some part, it doesn't explain near 100% regioselectivity. More important in determining regiochemistry, I ...
ringo's user avatar
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11 votes
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Regioselectivity of bromination of alkenes

With bromination, the first step is the formation of an adduct complex, which can be explained that the π-bond polarises the dibromide. The next step is the formation of the bromonium ion, which ...
Martin - マーチン's user avatar
10 votes
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Intramolecular lactonisation in an unsaturated carboxylic acid

The reaction as you are given turns up no results in SciFinder, meaning it has not been reported in any scientific journal. It is thus the imagination of whoever set the test. However, closely ...
Jan's user avatar
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8 votes
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Does rearrangement take place in the reaction between ethenylcyclohexane and iodine chloride?

Yes, I believe the rearrangement can happen. However, the product from the rearrangement is probably not the major one. The closest reaction to what you have drawn that I could find on SciFinder is ...
S R Maiti's user avatar
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8 votes
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Product of oxymercuration-demercuration reaction

Well, the answer is correct except instead of -OH it must be -OMe because the reagent used is Hg(OAc)2/ MeOH and not Hg(OAc)2/H2O. Here's an illustration of the rection using methanol
daf's user avatar
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7 votes
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Reaction of alkane with alkene in acidic medium

This reaction is actually called as "alkylation of alkenes". If I had known this term, I could have directly searched it on internet but won't have asked it on SE ;) https://chem.libretexts....
Ritil's user avatar
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6 votes
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Stereoselectivity of ring closure in intramolecular iodolactonisation

The results of the iodolactonization example presented in this question were published in 1982 by Bartlett, et al.1 While @Aniruddha Deb has captured the essence of the reaction, there is more than ...
user55119's user avatar
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5 votes
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Why doesn't the bromide anion attack during electrophilic addition of bromine in methanol solvent?

There's a very simple explanation for this. Your reasoning regarding $\ce{Br-}$ being a better nucleophile is absolutely correct. The reason as to why methanol attacks instead of $\ce{Br-}$ is because ...
Avyansh Katiyar's user avatar
5 votes
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Method for regioselective hydroalkylation of terminal alkyne

Here is a potential solution using old-school chemistry, though with several steps. Hydroborate the alkyne and work up with $\ce{H2O2}$ to give the aldehyde. Alkylate the aldehyde enolate with $\ce{...
Waylander's user avatar
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5 votes
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Anti-Markovnikov addition of HCl

One way to do it would be do first do a hydroboration-oxidation reaction, which leads to the anti-Markovnikov addition of $\ce{H2O}$. So you will get an $\ce{-OH}$ group instead of $\ce{-Cl}$. Then, ...
booma vijay's user avatar
5 votes
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How can a β,γ-unsaturated ketone be converted to 1-pyrroline?

I suggest two possible approaches. Narasaka, et al. have effected similar cyclizations photochemically. I prefer to start with the allylic alcohol 1 to avoid complications with oxime formation. ...
user55119's user avatar
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5 votes
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Electrophillic susbtitution of bromine on styrene and cinnamic acid in the presence of FeBr3, a Lewis acid

In electrophilic aromatic substitution the activation energy is very high ( as it should be, since the aryl carbocation transition state is very unstable) The role of $\ce{FeBr_3}$ or any lewis acid ...
napstablook's user avatar
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5 votes
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What is the meaning of a “halide component” for Friedel–Crafts reaction?

Friedel–Crafts reactions proceed through the alkylation or acylation of an aromatic ring using an alkyl halide. Considering the alkyl halide compound of the form $$\ce{R-X}$$ where $\ce{R}$ is the ...
cayji's user avatar
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4 votes

Stereoselectivity of ring closure in intramolecular iodolactonisation

Without further details, I would say that both products are possible. The reaction that you have given here is an Iodolactonization reaction. You have correctly identified that the tert-butyl group ...
Aniruddha Deb's user avatar
4 votes
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What are the products of alkene oxymercuration with diols?

There are so many structures here that it is at times difficult to keep things straight. The best way to approach your question is to take advantage of what is known about oxymercuration. If you enter ...
user55119's user avatar
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4 votes

Bromonium ion or Mesomeric effect ( intermediate during addition to alkenes)

You are not going to see the formation of a primary carbocation—the activation energy is too high. Even though it is true the following are resonance structures of one another: the geometry in which ...
ringo's user avatar
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4 votes
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Why must polymers have a repeating unit?

Entropy would favour a random orientation of each monomer unit when building up the chain, however whenever you have two different substituents at the ethylene unit, then electrostatics and sterical ...
Karl's user avatar
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4 votes
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Conjugate addition vs Electrophilic addition

Grignards unless modified with Cu(I) salts add 1,2 not 1,4 so the EtMgBr will add to the ketone to give the t-alcohol and leaving the double bond intact. Consider then the HCl step - if it is strong ...
Waylander's user avatar
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4 votes
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Why do more substituted alkenes undergo epoxidation, but the less substituted alkenes undergo hydrogenation?

As you already know, the alkene has to approach the catalyst surface in the first step. For optimum adsorption, the molecule must be able to orient itself parallel to the surface of the metal. Less ...
Avyansh Katiyar's user avatar
4 votes
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Product of the addition of 1 eq. bromine to 1-methylcyclohexa-1,4-diene

You misunderstood what hyperconjugation is. It occurs when the electrons in a $\ce{C-H}$ $\sigma$-bond are shared with an adjacent atom's empty or partially filled $\mathrm{p}$-orbital, giving the ...
ringo's user avatar
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4 votes
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What are the major products when naphthalene reacts with ethyl chloride in the presence of AlCl₃?

TL;DR: The final product will depend on what solvent you are using, what temperature the reaction is being operated and the concentration of the reactants. Long answer From the abstract of this paper1:...
Nilay Ghosh's user avatar
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3 votes

Why does bromine add to a double bond instead of a triple bond if both are present?

I'm going to take "more reactive" as in the alkene undergoes bromination at a faster rate than the alkyne, which seems to imply that the activation energy of the transition state is greater. A ...
dlq's user avatar
  • 226
3 votes

Does rearrangement take place in the reaction between ethenylcyclohexane and iodine chloride?

In Bull. Chem. Soc. Jpn. 1983, 56 (1), 314–317, a paper dealing with the kinetics of addition of $\ce{ICl}$ to alkenes, the following mechanism is proposed This may lead to the conclusion that the ...
Safdar Faisal's user avatar
3 votes
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The dependency on electron density in the reactivity order of electrophilic and nucleophilic additions

After not having any answer for over a week, I wrote about this question in the comments of an answer I had posted to another question. There another user confirmed that the reasoning I have given in ...
TRC's user avatar
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3 votes
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Major product formed when HBr is added to 1-phenyl but-2-ene

Phenyl groups are bulky and cause steric hindrance. This makes the $\ce{Br^-}$ nucleophile have an easier time targeting the carbon atom in the double bond that's closer from the right side of the ...
Sam202's user avatar
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2 votes

Ozonolysis of alkene

When the ozonide is reduced to Ketone/Aldehyde, We're concerned with what is called the "reductive workup" . We can summarize it like this: If we look a little further into the mechanism (...
sai-kartik's user avatar
2 votes
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Can someone explain my professor's answers for these alkene additions?

In example A, you are right that the cyclohexane ring is more stable than the cycloheptane ring. There are two choices for rearrangement in this case: 1) Ring expansion to form the cycloheptane ring ...
Eli Jones's user avatar
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2 votes

Markovnikov Rule of Alkenes

My suggestion is to stop trying to predict the product by rules like “rich becomes richer” or “proton goes to carbon having greater number of hydrogens attached to it”, etc. for Markovnikov addition ...
user600016's user avatar
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2 votes
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Why alkyl shift happens during hydroboration oxidation?

But why does this happen? Well, if it was a plain old carbon in the middle, this migration wouldn't happen. It would sit there forever. Boron isn't carbon, though: it has fewer protons, is less ...
orthocresol's user avatar
2 votes

Reaction of vinylacetylene (but-1-en-3-yne) with HCl

Beyond a shadow of a doubt, the second explanation, involving an allene rearrangement is the correct one. As you said, alkenes are more reactive towards electrophilic addition and hence the addition ...
Thenard Rinmann's user avatar

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