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Questions tagged [chemoselectivity]

For questions about selectivity between different functional groups.

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Can Weinreb amides be used to form 1,3 dicarbonyl compounds?

Weinreb amides are useful in reducing acid chlorides (and esters) to form ketones due to the fact that the more reactive keto group is unmasked only after treatment with acid and water, which destroys ...
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1answer
215 views

Why is a Grignard reagent not protonated by chloramine?

When $\ce{RMgX}$ (Grignard reagent) reacts with chloramine ($\ce{NH2Cl}$) it forms $\ce{RNH2}$. But why doesn't it form $\ce{RH}$ by taking a hydrogen atom from chloramine as the negative charge so ...
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1answer
464 views

Reaction of hydrazine and hydroxylamines with carboxylic acids

Carboxylic acids and their derivatives on reaction with hydroxylamine $\ce{NH2OH}$ and hydrazine $\ce{N2H4}$ give hydroxamic acids and acid hydrazides, respectively, through acyl nucleophilic ...
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347 views

Why is the nitrile group not hydrolyzed as well during hydrolysis of imine in Thorpe reaction?

while imine is getting hydrolysed, why does not nitrile group hydrolyse to give carboxylic acid?
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1answer
321 views

Single electron reduction of ketone by Na or Zn

Whenever we add Na or Zn metal to a ketone, why does the electron prefer to attack the carbonyl bond and form a radical, instead of removing the acidic hydrogen and forming an enolate and $\ce{H2}$ ...
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1answer
4k views

Why does the Rosenmund reduction stop at the aldehyde stage?

In the Rosenmund reduction, an acyl chloride can be reduced to an aldehyde by hydrogenation over a palladium catalyst poisoned with barium sulfate. Why isn't the aldehyde product further reduced to ...
6
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1answer
840 views

Monoepoxidation of 1,2-dimethylcyclohexa-1,4-diene using m-CPBA

What is the product formed when 1,2-dimethylcyclohexa-1,4-diene undergoes epoxidation with one equivalent of m-CPBA (meta-chloroperbenzoic acid)? In the epoxidation mechanism, the π-electrons ...
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Why does magnesium prefer to insert into C–Br bonds over C–Cl bonds?

In the formation of a Grignard reagent from a compound possessing both bromine and chlorine, magnesium preferentially inserts into the C–Br bond over the C–Cl bond. For example, the formation of a ...
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2answers
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Reduction of a ketone in the presence of an aldehyde

An aldehyde group can easily be reduced to an alcohol using the mild reducing agent $\ce{NaBH4}$ at low temperature in the presence of a ketone group. This chemoselectivity is due to the fact that an ...
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1answer
68 views

Selective transfer of least/most stable anion from organometallic reagents

When heterocuprate reagents participate in conjugate addition, the least stable anion is transferred from copper to the electrophile: On the other hand, palladium-catalysed cross-coupling reactions ...
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1answer
299 views

Can an ether be selectively hydrolysed in the presence of an ester?

What reaction, or protection/deprotection can be used to transform the ether group of a molecule that also has an ester compound into an alcohol while keeping the ester unchanged? For example: The ...
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1answer
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Chemoselectivity in reduction of 3′-nitroacetophenone

When 3′-nitroacetophenone is treated with sodium borohydride, only the carbonyl group is reduced (top); however, when reacted with tin and hydrochloric acid only the nitro group is reduced (bottom). ...
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Why does bromine add to a double bond instead of a triple bond if both are present?

According to my textbook, the addition of bromine to pent-1-en-4-yne at low temperature yields 4,5-dibromopent-1-yne: Why does bromination of the double bond occur selectively?
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1answer
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Can a benzyl ether be removed in the presence of an ester?

I'd like to deprotect a benzyl group for a Fráter–Seebach alkylation. Would it be possible to do this with a Birch reduction using Li/NH3 (or Na/NH3), without also reducing the ester carbonyl group? ...
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1answer
380 views

How can a ketone be enantioselectively reduced, in the presence of an ester?

I'd like to reduce enantioselectively a ketone in presence of an ester (which should NOT be reduced to an aldehyde and further to an alcohol). Adding $\ce{LiAlH4}$ would also reduce the ester and ...
13
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1answer
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Why do BH3 and NaBH4 have different selectivities?

I've always known borane ($\ce{BH3}$), as a reagent for alkene hydroboration. Recently in class we talked about its use in the reduction of carboxylic acids to alcohols as well. Now obviously $\ce{...
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1answer
814 views

Selective alkylation of carboxylic acid versus phenol

Starting from the ketone shown, I plan to use a haloform reaction to transform the acetyl group into a carboxylic acid. Following that, there are two alkylations to be carried out: one esterification ...
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2answers
1k views

How can an aromatic ketone be reduced in the presence of a nitro group?

Is it possible to reduce an acyl group to an alkane, but still keep a nitro group intact without its reduction to an amino group? A Clemmensen reduction would reduce the nitro group, and it seems like ...
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1answer
5k views

Selectivity in aldol condensation between pivaldehyde and acetone

In a crossed aldol condensation (condensation between aldehyde and a ketone), the primary products are such, that the carbonyl group of the ketone remains intact, and the $\alpha$-hydrogen of ketone ...
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2answers
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Why are fluorides more reactive in nucleophilic aromatic substitutions than bromides?

In nucleophilic aromatic substitution reactions, why do fluorides react faster than bromides? Ordinarily bromide is a better leaving group than fluoride, e.g. in $\mathrm{S_N2}$ reactions, so why isn'...