Questions tagged [regioselectivity]

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

Filter by
Sorted by
Tagged with
51
votes
2answers
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
1answer
124 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
2answers
66 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 ...
32
votes
1answer
30k 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
1answer
738 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
1answer
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
1answer
73 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
1answer
101 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
1answer
91 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 ...
0
votes
0answers
13 views

What are the unique reactions of conjugated carbon containing carbonyl compounds?

Various sources give different ideas about the reduction reaction of α,β-unsaturated carbonyl compounds which have conjugated carbon. Just like cinnamaldehyde do aliphatic α,β-unsaturated carbonyl ...
9
votes
2answers
373 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 ...
5
votes
2answers
537 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 ...
20
votes
1answer
41k 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
1answer
933 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
1answer
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
1answer
181 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
1answer
135 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 ...
3
votes
2answers
212 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
0answers
61 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
2answers
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
1answer
106 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
1answer
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 ...
2
votes
1answer
2k views

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 ...
1
vote
0answers
72 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
1answer
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
1answer
594 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
0answers
294 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 ...
15
votes
2answers
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 ...
2
votes
1answer
78 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
1answer
138 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 ...
13
votes
1answer
11k 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
0answers
79 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 $\alpha,\beta$-...
7
votes
1answer
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
1answer
256 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
0answers
675 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
2answers
187 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
1answer
963 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) $\ce{LiAlH4}$, ...
25
votes
2answers
4k 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-...
7
votes
2answers
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
1answer
535 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 ...
16
votes
1answer
12k views

Regioselectivity in electrophilic substitution of pyrrole

In the electrophilic aromatic substitution (EAS) of pyrrole, why is the alpha position preferred over the beta position so much?
1
vote
1answer
6k 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 ...
2
votes
0answers
801 views

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 ...
1
vote
1answer
2k views

What is Markovnikov's rule?

What is Markovnikov's rule? How can we use it to predict the products of additions to alkenes? And is it always obeyed, or are there exceptions to this rule?
2
votes
0answers
469 views

Selectivity in Suzuki coupling of 2,4-dichloropyrimidine

I've seen many papers (see e.g. Synthesis 2010, 16, 2721–2724) in which the 4-chloro group of 2,4-dichloropyrimidine is selectively reacted under Suzuki coupling conditions. Is there any way where ...
2
votes
1answer
672 views

Why should epoxides be more reactive at a position where positive charge is stabilised?

In the above reaction, I am told that the nucleophilic chloride anion attacks the trisubstituted carbon because it has the most partial positive character due to its ability to stabilize positive ...
3
votes
1answer
1k views

Regioselectivity in Kharasch addition of bromotrichloromethane

When hex-1-ene is treated with bromotrichloromethane in the presence of a peroxide initiator (e.g. dibenzoyl peroxide), what is the regioselectivity of the addition? I know that the radical addition ...
3
votes
2answers
27k 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 ...
6
votes
1answer
1k views

Is there any selectivity between the C-2 and C-4 positions of pyridine in SNAr reactions?

In nucleophilic aromatic substitution (SNAr) reactions on pyridines, displacement of leaving groups at C-2 and C-4 is favoured because the negative charge in the intermediate can be delocalised onto ...
4
votes
1answer
5k 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 ...