Questions tagged [regioselectivity]

For questions involving selectivity as to where a functional group reacts.

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Regioselectivity in oxo-Diels-Alder reaction

I have one doubt about the dimerization of methacryloyl chloride into the product 3: The dimerized product was observerd around 10-15mol% in different commercial samples of methacryloyl chloride, as ...
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4 votes
1 answer
57 views

Regioselectivity of the Hydroboration and Epoxidation of Limonene

Could someone help me out with the most likely major products for each reaction? 1 eq. of reagent is used for both reactions, so my initial thought was that both processes would only occur at the C=C ...
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Do rearrangements occur in oxymercuration and demercuration?

My book (Morrison & Boyd) says that rearrangements are possible in this reaction; unfortunately, it is just written and no examples are provided. So do rearrangements occur in oxymercuration / ...
0 votes
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59 views

Retrosynthesis of (1S,2R)‐1‐isopropyl‐2,4‐dimethylcyclohexane

I think that retrosynthesis of (1S,2R)‐1‐isopropyl‐2,4‐dimethylcyclohexane involves the opening of an epoxide, to control the regiochemistry in order to achieve the trans-configuration via an SN2 ...
2 votes
1 answer
71 views

Regioselectivity of SN2 reaction on adenine

I found the following question in my examination: I was able to make out from the options that the usage of a base is to remove the supposedly acidic hydrogen from either the Nitrogen $A$ or $B$. ...
5 votes
2 answers
100 views

Why is the major product of an elimination reaction an alkyne and not the diene?

1,2-Dibromopropane and KOH react together to form propyne. But I wondered if 1,2-propadiene was also being produced since the there is also a proton on the $\ce{CH3}$ group to be used in the ...
2 votes
0 answers
46 views

Regioselectivity of hydroboration-oxidation of enol ethers

In the book Hydroboration and Organic Synthesis, on p. 99, it is written that: hydroboration [of enol ethers] proceeds regioselectively, placing essentially all of the boron atoms at the β position ...
4 votes
1 answer
80 views

Regioselectivity in the opening of 3-membered heterocycles

(a) Consider the following reactions : For these two reactions, the nucleophile attacks the less substituted carbon as it is less sterically hindered. (b) Now consider the following reactions : For ...
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2 votes
1 answer
105 views

Chain transfer in polystyrene synthesis

while I was studying the many side reactions of radical polymerization, I stumbled across this source which illustrates the chain transfer side reaction in polystyrene synthesis: Of course, there is ...
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8 votes
1 answer
202 views

Why does LiAlH4 reduce the double bond of cinnamaldehyde, whereas it does not reduce the double bond in crotonaldehyde?

$\ce{LiAlH4}$ is a strong reducing agent capable of breaking the double bonds. It does break the double bonds in cinnamaldehyde. Shouldn't $\ce{LiAlH4}$ be able to break the double bond in ...
2 votes
2 answers
224 views

Is regioselectivity affected by steric factors during alkylation of naphthalene?

I read that Friedel Craft's alkylation of naphthalene by alkyl halides having more than 2 carbons occurs at 2-position. On the other hand, with smaller halides, it occurs at the 1-position. Does it ...
2 votes
1 answer
134 views

Regioselective enolate formation, choosing major and minor products

This question came in my organic chem assignment. The options highlighted are the answers. The end carbon(adjacent to the carbonyl group) should have more acidic alpha-hydrogen and the alkene formed ...
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1 vote
1 answer
199 views

How to explain regioselectivity in nucleophilic aromatic substitution

I’m trying to rationalise the major regioisomeric product of the following reaction of an arylchloride in the presence of sodium amide: I have predicted that the para-substituted product is formed as ...
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1 vote
1 answer
200 views

Regioselectivity of electrophilic addition of Halogen and Water (Halohydrin) on Alkenes?

I am currently studying for an organic chemistry exam and I just couldn't come up with a solution to the following question: Consider the reaction of 1-Propene + Br2 with water as solvent. Why will ...
1 vote
1 answer
1k views

activating and deactivating groups and directing effect

In electrophilic aromatic substitution: I have just learnt a 'rule' about benzene with more than 1 substituents attached (excluding the effect on steric hindrance): if a strong activating group (EDG) ...
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2 votes
1 answer
323 views

Regioselectivity in coupling reactions of α-naphthol

I have seen in the following reaction of azo coupling where coupling takes place at position 4 of $\alpha$-naphthol. Now the electron density accumulation is similar at both position $4$ as well as $...
4 votes
1 answer
167 views

Method for regioselective hydroalkylation of terminal alkyne

I'm trying to figure out a method to add a linear alkyl chain R and a hydrogen atom H across the triple bond of a terminal alkyne. The alkyl chain should end up on the internal carbon (C-2): My ...
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2 votes
0 answers
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Which way is major in this interesting intramolecular SN2 reaction to form different five memeber ring? [closed]

Which direction of the intramolecular reactions is major and why? Could someone could depict the mechanism step by step and it is better to draw out the transitional state configurations
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2 votes
1 answer
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How to achieve regioselective (base-catalyzed) enolization of a carbonyl group in a diketone?

One can convert a ketone to an enolate, either base- or acid-catalyzed. Let's say you now have a diketone. You choose to treat this compound with base (e.g. hydroxide anion, alkoxide anion, LDA/THF, ...
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1 vote
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What are some possible classification tests that one can use for o-nitrobenzoic acid?

I have analyzed an IR spectrum and found out that my compound (o-nitrobenzoic acid) has a nitro group, carboxylic group, and benzene ring. I was curious to know: if regioselectivity effects the ...
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4 votes
1 answer
806 views

Can someone explain my professor's answers for these alkene additions? [closed]

(a) Why would cyclohexane expand into cycloheptane? Cyclohexane is stable. (b) Why would cyclopentane not ring expand into cyclohexane? In the process a tertiary carbocation would be formed just like ...
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2 votes
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Why do the induction effects of fluorobenzene decrease electrophilic addition reactivity, conjugation effects increase selectivity?

Fluorobenzene shows signs of both the electron withdrawing and electron donating groups on benzene. Electrophilic substitution to the ring is less reactive because the fluorine is very electronegative ...
3 votes
1 answer
109 views

Bromohydration regioselectivity

In which of these cases would the addition of $\ce{Br2/H2O}$ be highly regioselective? $$\ce{CH3CH=CHCH2CH3}$$ or $$\ce{(CH3)2C=CH2}$$ since both are asymmetric alkenes, how do I answer the question?...
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4 votes
1 answer
329 views

Stereochemical outcomes in opening of vinyl epoxides

Explain the outcomes of the following reactions. In each case the major product is shown. Firstly, I don't understand why the chloride always attacks on the right hand side of the epoxide. Also,...
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1 answer
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Why is the major product of the reaction of 1-naphtol with benzene diazonium chloride not the ortho product?

If 1-napthol reacts with benzene diazonium chloride, it gives the para product with respect to the hydroxyl group. However, shouldn't the major product be the ortho one, because there will be ...
4 votes
2 answers
680 views

Why is a 7-endo radical cyclisation favoured over a 6-exo in this synthesis?

Normally, according to Baldwin's rules, 3-exo to 7-exo cyclisations are preferred over endo cyclisations. But in the following example, a 7-endo-trig reaction is favoured over a 6-exo-trig and I am ...
17 votes
2 answers
4k views

Does aniline react with diazonium ions at C or N?

In the azo coupling of aniline with benzenediazonium cation, I thought of two possible products 1 and 2 that could be formed. However, I can't work out which will be preferred. What would be the major ...
5 votes
2 answers
213 views

Regioselectivity in iodolactonisation of γ,δ-unsaturated carboxylic acid

In the last step of the iodolactonisation of 3,3-dimethylpent-4-enoic acid,[1,2] why does the carboxylate attack the iodonium to form a 5-membered ring, when a more stable 6-membered ring is possible? ...
3 votes
1 answer
839 views

How does base size affect the ratio of kinetic/thermodynamic enolate?

One of the factors that favor kinetic products is bulky bases. So, I'd expect that, for a certain substrate, the use of a more bulky base to favor even more the kinetic product. However, in the table ...
5 votes
1 answer
7k views

Why does nucleophilic aromatic substitution occur at C-2 and C-4 of pyridine?

In the following reaction of 2,3,4-tribromopyridine with sodium methoxide in methanol,[1] why are only the C-2 and C-4 bromines replaced with methoxy groups? Why doesn't the bromine at C-3 also get ...
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20 votes
1 answer
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Regioselectivity of epoxide hydrogenation using Pt versus Ni catalyst

What conditions are applicable for the transformations X and Y, respectively? (a) $\ce{LiAlH4}$, and $\ce{NaBH4}$ (b) $\ce{NaBH4}$, and $\ce{BCl3}$ followed by $\ce{NaBH4}$ (c) $\ce{LiAlH4}$, ...
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8 votes
2 answers
1k views

Claisen rearrangement in substituted ring

This is an example of Claisen rearrangement, property of allyl vinyl/phenyl ethers. I believe that the allylic migration should take place to the position ortho to both $\ce{-CH3}$ and $-\ce{OR}$ ...
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8 votes
2 answers
416 views

Selectivity in aldol condensation of 7-oxo(6,6-²H₂)octanal

I am supposed to find the product of the following reaction: I know that six-membered rings are more stable than five-membered rings, but the C-D bonds are stronger, so it confuses me where will the ...
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2 votes
0 answers
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Reactivity and selectivity in free radical halogenation of alkanes

I read about the free radical halogenation of alkanes with $\ce{X2}$ and I have the following questions: Given that the first step is the homolytic breaking of the $\ce{X-X}$ bond, and the homolytic ...
10 votes
1 answer
684 views

How does Hofmann elimination work in this reaction?

In my Chemistry class, we were given this question to solve, and I'm not sure I fully understood the solution. I understand that since the substrate is bulky, Saytzeff elimination can't happen, so it ...
1 vote
1 answer
7k views

Why does radical chlorination and bromination of propane occur at different positions?

When propane reacts with chlorine, we will mostly (theoretically) get an isomer with a chlorine on the end. ($\ce{CH_3-CH_2-CH_2Cl}$). However, when propane reacts with bromine, we will mostly get an ...
14 votes
1 answer
680 views

Most activated position on para-terphenyl for EAS

Para-terphenyl: it doesn't look pretty with all those math-y numbers, but those are going to come helpful in answering my question! A question asked me to tell the expected product when this reacts ...
6 votes
1 answer
1k views

Regioselectivity in Claisen condensation and aldol reaction

I'm having a hard time determining regio-selectivity in those two reactions. At the image above I've drawn one example for each on of them. My question is how do we choose where the deprotonation ...
7 votes
0 answers
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How can organocuprates generated with catalytic Cu(I) be competitive in 1,4-addition to an enone?

Organocopper compounds (e.g. $\ce{LiCuR_2}$) are often prepared from an organolithium or Grignard reagent when a soften nucleophile is needed, such as for a conjugate addition to an $\alpha,\beta$-...
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Why do t-butyl bromide and silver(I) nitrite form the nitroalkane, not the nitrite ester?

We know that reaction of $\ce{AgNO2}$ with alkyl halides is SN1 type reaction and follows HSAB principle. So in the reaction of $\ce{(CH3)3C Br}$ we would expect $\ce{AgBr}$ to form and also a ...
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5 votes
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Stability of extended enolates

I'd expect an extended enolate to be more stable than a normal enolate, when both can form, but my textbook suggests otherwise. What is the stability of an extended enolate compared with a normal ...
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14 votes
1 answer
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Why does LiAlH4 reduce the double bond of cinnamaldehyde, whereas NaBH4 does not?

I read an answer here about why $\ce{LiAlH_4}$ does not reduce conjugated double bonds, and that $\ce{NaBH_4}$ does. But in the case of cinnamaldehyde, $\ce{LiAlH_4}$ reduces the conjugated double ...
3 votes
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Regioselectivity in the aldolcondensation towards (Z)-Jasmon

In the synthesis of (Z)-Jasmone via aldol-condensation as shown below, how can the observed regioselectivity be explained? After all, it is also possible to form the side product shown below. I ...
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0 votes
1 answer
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Deciding which α-Η gets abstracted in aldol condensation

Consider the base catalysed aldol condensation of methyl ethyl ketone. The first step involves the abstraction of a proton by the base. However I am having trouble deciding whether the proton will be ...
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1 vote
1 answer
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Carbocation formation in electrophilic addition of hydrogen halides to alkenes

Question: My attempt: I made the carbocation on the carbon labelled $1$ because I think that the positive charge would be slightly more stable on $1$ compared to $2$ due to the inductive effect of $\...
1 vote
1 answer
415 views

Nonsubstituted Cycloalkene HBr Reaction

If I have a cyclohexene with no substituents and add HBr, how do I know what side of the former double bond to place the Br anion? I think I understand Markovnikov's rule, but in my chemistry book ...
-2 votes
1 answer
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Why is isopropylbromide formed as the major product but not n-propylbromide from 1-propene?

When 1-propane reacts with HBr, the major product formed is isopropyl bromide and minor product is n-propyl bromide. I know that this is said to happen because the reaction mechanism favours the ...
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7 votes
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Why does phenol react on oxygen in the Gattermann–Koch reaction?

When discussing the Gattermann–Koch reaction on phenol substrates, it has been said that O-acylation is a problematic competing reaction as in a phenol, there's high electron density on the O atom [...
2 votes
1 answer
107 views

Separation of alkylated 1,2,4-triazole in solution

I was looking into heterocyclic compounds and their alkylation (i.e. the regioselectivity of the alkylation of the compound). People are able to give pretty exact numbers, for an experiment done in ...
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9 votes
2 answers
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Nucleophilic aromatic substitution on pyrimidines: C2 vs C4 selectivity

[There are many similar questions on Chemistry.SE (e.g. 1, 2) and a quick search will reveal all of them, but nothing on this in particular.] The reaction of 2,4-halopyrimidines with nucleophiles ...
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