Questions tagged [regioselectivity]

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

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1 answer
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Why does sulfonation of aniline occur para rather than ortho?

According to a textbook by K. L. Chugh: Sulfonation [of aniline] is a reversible reaction. The p-isomer, being more stable, does not get desulfonated easily. Hence, p-sulfanilic acid is the major ...
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 $B$. ...
3 votes
0 answers
29 views

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 ...
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 ...
1 vote
3 answers
416 views

O-carboxylation in the Kolbe–Schmitt reaction

In the Kolbe–Schmitt reaction, we know that the pi electrons of the benzene ring attack the carbon in carbon dioxide, but why doesn't the reaction occur on oxygen instead (as shown in the diagram ...
0 votes
0 answers
37 views

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
0 answers
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 ...
26 votes
2 answers
5k views

Electrophilic Aromatic Substitution: Are protonated OH-groups ortho-/para- or meta-directing?

In Electrophilic Aromatic Substitution ($\text{S}_{\text{E}}\text{Ar}$) reactions groups that can donate an electron pair into the aromatic ring, e.g. $\ce{-OH}$ or $\ce{-NH2}$, are ortho-/para-...
5 votes
2 answers
99 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 ...
5 votes
2 answers
28k views

Why can toluene be chlorinated at either the benzylic position or the ring depending on the conditions?

My book mentions a reaction for the preparation of benzaldehyde with toluene in which side chain chlorination of toluene gives (dichloromethyl)benzene, which upon hydrolysis gives benzaldehyde: Why ...
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 ...
51 votes
2 answers
16k views

Regioselectivity of acid-catalyzed ring-opening of epoxides

Not to be confused with what is the mechanism of acid-catalyzed ring opening of epoxides. What is the correct order of regioselectivity of acid-catalyzed ring-opening of epoxides: $3^\circ$ > $2^\...
8 votes
1 answer
201 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 ...
35 votes
1 answer
34k views

Is the ammonium substituent (-NH3+) really meta-directing in electrophilic substitution?

If we make a resonance structure for the anilinium ion, with positive charge at either the ortho or the para position, we get a pentavalent nitrogen, which is not possible. So, how is the $\ce{-NH3+}$ ...
3 votes
1 answer
816 views

Preference of certain positions during chlorination of an alkene

I am currently doing the questions: Write equations for the reaction of chlorine with propene and 2-butene using structural formulas. So I know that propene is $\ce{H3C-CH=CH2}$ and chlorine is $\ce{...
11 votes
1 answer
1k views

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

In the hydroboration of a typical alkene, the boron fragment ends up attached to the less substituted carbon: What are the electronic or steric factors that lead to this regioselectivity?
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 ...
1 vote
1 answer
198 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 ...
1 vote
1 answer
199 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 ...
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 ...
4 votes
2 answers
679 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 ...
21 votes
1 answer
44k views

Why does NaBH4 reduce double bonds conjugated to carbonyl groups, while LiAlH4 does not?

I have been going through reduction of aldehydes using $\ce{LiAlH4}$ and $\ce{NaBH4}$. If there is a double bond conjugated with the carbonyl group, $\ce{LiAlH4}$ doesn't reduce it, leading to an ...
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) ...
11 votes
1 answer
6k views

Regioselectivity in electrophilic aromatic substitution of benzofuran and indole

Why does benzofuran react preferentially at position 2 when nitrated or formylated, while indole reacts preferentially at position 3 (source: Joule and Mills, Heterocyclic Chemistry 5th ed., p 371)?
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 ...
4 votes
2 answers
226 views

Regioselectivity in nitration of a 1,2-disubstituted aromatic compound

For 1,1,4,4-tetramethyl-1,2,3,4-tetrahydronaphthalene: What would be the products following a standard nitration with $\ce{NO2+}$? My reasoning is thus: Since the substituent group is alkyl then it ...
2 votes
0 answers
69 views

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
9 votes
2 answers
2k views

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 ...
2 votes
1 answer
127 views

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, ...
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 ...
1 vote
0 answers
90 views

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 ...
13 votes
1 answer
3k 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 ...
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 ...
2 votes
0 answers
409 views

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 ...
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 ...
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?...
0 votes
1 answer
149 views

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 ...
14 votes
1 answer
14k views

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 ...
7 votes
0 answers
94 views

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 $\alpha,\beta$-...
8 votes
1 answer
17k views

Which is the major product formed on nitration of benzyl methyl ether?

Which is the major and minor product formed from the reaction of benzyl methyl ether with dinitrogen pentoxide? I know that $\ce{NO2+}$ is behaving as an electrophile here and attacking the aromatic ...
4 votes
1 answer
328 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,...
5 votes
0 answers
702 views

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 ...
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? ...
20 votes
1 answer
1k views

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) $\ce{LiAlH4}$, ...
7 votes
2 answers
2k views

Hydroboration/oxidation vs acid-catalyzed hydration of 1-phenylpropene

I am trying to predict the products of both the hydroboration/oxidation and acid-catalyzed hydration of 1-phenylpropene: Both C1 and C2 of the double bond are secondary carbons. However, I have the ...
3 votes
1 answer
836 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 ...