Questions tagged [regioselectivity]
For questions involving selectivity as to where a functional group reacts.
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Regioselectivity of hydroboration-oxidation of heterocyclic olefins
In the book Hydroboration and Organic Synthesis, on p. 99, it is written that:
hydroboration [of heterocyclic olefins] proceeds regioselectively, placing essentially all of the boron atoms at the β ...
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1answer
64 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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1answer
60 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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1answer
135 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 ...
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2answers
79 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 ...
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1answer
82 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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1answer
123 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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1answer
112 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 ...
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1answer
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) ...
2
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1answer
204 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 $...
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144 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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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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1answer
113 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, ...
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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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1answer
679 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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309 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 ...
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1answer
86 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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1answer
272 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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1answer
140 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 ...
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2answers
579 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 ...
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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 ...
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2answers
192 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? ...
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1answer
598 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 ...
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1answer
6k 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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1answer
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) $\ce{LiAlH4}$, ...
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2answers
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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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2answers
380 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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0answers
840 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 ...
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1answer
646 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 ...
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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 ...
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1answer
559 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 ...
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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 ...
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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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679 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 ...
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331 views
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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1answer
12k 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 ...
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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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1answer
115 views
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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1answer
607 views
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 $\...
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1answer
387 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 ...
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1answer
679 views
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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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 [...
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1answer
103 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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2answers
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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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1answer
290 views
Ring opening of aziridinylmethyl and oxiranylmethyl radicals
When a radical is alpha to a three-membered ring, it is common for the ring to open via β-scission (to relieve ring strain):
When the ring contains a heteroatom there are a couple of different ...
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1answer
426 views
Selectivity in acetonide formation from a polyol
In my total synthesis lecture notes the above example is given in which a polyol is reacted under acetonide forming conditions.
The notes point out that this product is the only product, no other ...
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1answer
397 views
Why is nitrosobenzene electrophilic on O in organocatalytic oxygenations?
In 2003 Zhong1 and MacMillan2 reported the use of nitrosobenzene, PhNO, in the organocatalytic asymmetric α-oxygenation of carbonyl compounds:
which is all nice, except for the slightly ...
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400 views
Sulfonyl azides: diazo or azide transfer?
Sulfonyl azides, $\ce{RSO2N3}$, are capable of acting as sources of electrophilic azide ("$\ce{N+3}$"), but are also capable of effecting diazo transfer, as shown in the scheme below, taken from ref 1:...
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1answer
3k views
Regioselectivity in Friedel–Crafts acylation of thiophene
In the above reaction, I understand that $\ce{AlCl3}$ is acting as a Lewis acid to generate an acylium ion, which is a strong electrophile.
Would this electrophile attack at carbon 2 or 3?
I think ...
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1answer
987 views
Regioselectivity in addition of hydrogen iodide to vinyl chloride
I encountered a question which was stated as:
The reaction of vinyl chloride with hydrogen iodide to give 1-chloro-1-iodoethane is an example of anti-Markovnikov addition. Is this true or false?
...
