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 ...
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11 votes
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What is the difference between "bromine" and "bromine water" in their reaction with an alkene?

From ChemGuide: Using bromine water as a test for alkenes If you shake an alkene with bromine water (or bubble a gaseous alkene through bromine water), the solution becomes colourless. ...
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Why does the chlorination of indene occur with syn selectivity in heptane?

Key The reaction is run in heptane, a non-polar solvent. A non-polar solvent will not stabilize or support ions as well as a polar solvent. Background When the $\ce{Cl2}$ begins to interact with ...
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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 ...
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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 ...
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9 votes
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Getting 3,4-dimethylhex-3-ene from but-2-ene

Your approach, which uses $\ce{Br2}$ to convert 2-butene into 2,3-dibromobutane and react that with ethylmagnesium bromide $\ce{CH3CH2MgBr}$ has two flaws: This approach removes the alkene and there ...
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What is Markovnikov's rule?

Markovnikov's rule is used to predict how (for example) HX, where X is a halide, adds to an unsymmetrical olefin. As the diagram below shows, Markovnikov addition follows the rule that the "H" will ...
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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 ...
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7 votes
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What is the stereochemistry resulting from hydroboration of 1-methylcyclopentene?

The second step is a syn addition of the boron hydride. As depicted below, it will result in an anti-Markovnikov product with the boron on the less-substituted carbon. Both hydrogen and boron are on ...
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What are the products of the reaction of 1-methoxycyclohexene with dilute hydrochloric acid?

Vinyl ethers are "masked" carbonyls, therefore in acidic aqueous environment the following pathway takes place: alkene protonation assisted by the methoxy group followed by nucleophilic attack of ...
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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....
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Addition reaction of hydroiodic acid to 2-bromo-3-chloro-2-butene

TL;DR - Sometimes you need to do the experiment. Like all questions involving Markovnikov's rule, you should compare the structures of the two carbocations: At C2 (Bromo) $$\ce{H3C-C(Cl)=C(Br)-...
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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 ...
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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, ...
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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. ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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4 votes

Getting 3,4-dimethylhex-3-ene from but-2-ene

Ben is right that your product is simple dimer of substrate. However, there is much easier approach to conduct dimersisation of butene - it happens easily if you use strongly acidic catalyst, like ...
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What are the products of the reaction of 1-methoxycyclohexene with dilute hydrochloric acid?

You're close. You are right in thinking that the first step involves protonation of the double bond. But which end of the double bond will you protonate? If you protonate the carbon bearing the ...
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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 ...
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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{...
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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 ...
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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:...
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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 ...
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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 ...
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3 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 ...
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