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Questions tagged [nucleophilic-substitution]

For questions having their focus on SN1, SN2, SNi, SN1', SN2', or SN2th (nucleophilic acyl substitution).

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When will acid-base reactions occur before substitution reaction

For example, given the reaction below: The substrate is secondary, the solvent is aprotic and it is to react with a strong bulky base. From this, I assumed that the reaction would be $\ce{E2}$. ...
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Why is the nucleophilic substitution of OH- with 1-bromopentane slower than with 2-bromo-2-methylbutane?

Which statement about the reaction of a hydroxide ion with the organic reagent is correct? A. 1-bromopentane predominantly follows an $\mathrm{S_N1}$ mechanism. B. 2-bromo-2-methylbutane ...
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Does a non-chiral substrate (2-bromo-2-methylpropane) also form two products via an SN1 mechanism?

If I have an alkyl halide, in which its tertiary carbon is non-chiral (for example 2-bromobutane), which reacts via an SN1 mechanism does it also produce 2 products? I am asking because I know that ...
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Why do we use LiCl as a source of chloride ions as nucleophile but not other alkali metal chlorides? [closed]

$\ce{LiCl}$ has higher covalent character than other alkali-metal chlorides, so in polar solutions like ethanol, its ioniztion will be less, and so less chloride ions will be available for ...
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1answer
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Why do polar aprotic solvents favour SN2 over E2?

I was reading about Substitution and Elimination Reactions and I came across the following on MasterOrganicChemistry: Polar protic solvents tend to favor elimination (E2) over substitution (SN2). ...
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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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Halogen bonding in organic reactions

Recently, a group of researchers from the Nanyang Technological University in Singapore have investigated the novel $\ce {S_N2X}$ mechanism which involves a "frontside attack" on the substrate, rather ...
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22 views

Do the mechanism (SN1 or SN2 ) which reaction follow depends more upon intermediate stability than on substrate and nucleophilic?

For eg : would the reaction of 3-methylbut-2-en-1-ol with HBr follow SN1 mechanism due to stability of your intermediate carbocation stability or SN2 due to the compound being primary alcohol and ...
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Why doesn't solvent form the major product in SN1 reactions?

If in a reaction SN1 pathway is followed then after the formation of carbocation the reagent or the solvent molecule can attack to form the product. As the number of solvent molecules are ...
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2answers
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Why is it aqueous and ethanolic conditions for nucleophillc substitution of cyanide ion with benzyl chloride?

I was doing an exam question where benzyl chloride was undergoing a nucleophilic substitution with cyanide ion to form benzyl cyanide. Please can someone enlighten me as I have never seen both ...
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Reaction of ketones with sodium amide

Find the product of the reaction of dimethyl ketone i.e. $\ce{CH3C(O)CH3}$ with $\ce{NaNH2}.$ Should I do nucleophilic addition and form the product in the picture?
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Why doesn't open-chain glucose react with water readily in aqueous solution?

Though the exact number given varies from 0.02% to 3%, it's well agreed that glucose spends a very small percentage of its time in aqueous solution as a linear aldehyde. Glucose's overwhelming ...
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Is isobutyl chloride or ethyl chloride more reactive in an SN1 reaction?

Compare the rate of $\mathrm{S_N1}$ reaction in the following compounds: We see that both compounds form primary carbocations. However, there is more hyperconjugation in the second compound as ...
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Which of these chlorides is more reactive? [duplicate]

We do learn that for $\mathrm{S_N1}$ reaction the rates are tertiary > secondary > primary > methyl. The reasons mentioned are usually inductive and hyper-conjugative effect. But which of the ...
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1answer
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Can the nitrogen of an amide displace a primary chloride in a S_N_2 reaction in the presence of a strong base?

I was looking at the following reaction and am confused. It appears that $\ce{N}$ is attacking the $\ce{C-Cl}$ and $\ce{Cl}$ is leaving in a $\mathrm{S_N2}$ reaction. I know that $\ce{Cl}$ is a good ...
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Why is this reaction not feasible?

The reaction is:$$NH_3+CH_3OCH_3 \rightarrow CH_3NH_2+CH_3OH$$ The mechanism here would be $S_N2$ and since $NH_3$ is a stronger base so it should be a better nucleophile. Why then is this reaction ...
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In nucleophilic acyl substitution, why will the Nu never displace the leaving group (e.g., Cl) directly by an SN2 mechanism?

In my class notes, it says: "The Nu will NEVER displace the leaving group directly in an SN2 reaction." We have previously been taught that SN2 reaction only occur at tetrahedral carbons, so I can ...
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Distinguishing between a nucleophilic substitution and an electrophilic substitution

Why don't we consider all nucleophilic substitution reactions as electrophilic reactions and vice versa? For example, look at this reaction I found in my textbook. (See picture) This is an ...
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1answer
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Confusion about the Sn1 and Sn2 Mechanism

My book says, and I understand, that the Sn1 mechanism is much faster for tertiary alkyl halides than primary. And the opposite for Sn2. This all makes sense. What I don't get is the conclusion it ...
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Why don't acyl chlorides give positive test with 2,4-DNPH?

In this post, Ron discusses the reasons why carboxylic acid derivatives such as amides, acids and esters do not give a positive result with 2,4-dinitrophenylhydrazine. He mentions that it is largely ...
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How many moles of methyl iodide will be consumed by one mole of crixivan?

My take on this question : a total of 5 moles of $\ce{CH3I}$ should be consumed. The oxygen atoms in the $\ce{2 OH}$ groups each have a lone pair of electrons. They should displace $\ce{I-}$ from ...
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Oxirane and ring opening

I have a problem given as :- I thought of a sn1 type mechanism in acidic medium and a sn2 pathway in basic medium . Am I correct or not . Please also check the mechanism according to which I formed ...
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1answer
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Bromination of but-3-en-1-ol in basic medium and Baldwin's rules

After formation of the bromocarbocation the alkoxide anion attacks the bromocarbocation which leads to ring formation and can proceed through two pathways 5 endo tet cyclization is disfavored but 4 ...
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Nucleophilic addition - Propanal vs Benzaldehyde

According to my school textbook, carbon atom of the carbonyl group benzaldehyde is less electrophilic than that of propanal because polarity of the carbonyl group is reduced in benzaldehyde due to ...
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1answer
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SN2 reactions with primary alcohols [closed]

A problem I was recently working on poses the following scenario: A student realizes that protonation of an alcohol makes the -OH into a better leaving group. Therefore, he suggested the following ...
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1answer
129 views

Order of reactivity of hydrogen halides

Solomon and Fryhle $11^{th}$ edition says : Order of reactivity of HX in the acid catalyzed conversion of alcohols to alkyl halides follows the order : HI>HBr>HCl We can account for this by saying ...
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1answer
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Reaction of cyclobutylmethanol with HX

I am interested in the reaction of cyclobutylmethanol with HX where these are the only reagents. My question is whether the reaction proceeds via SN1 or SN2. My reference text insists that primary ...
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1answer
57 views

What is the expected number of rings obtained in the following ring formation process?

Refluxing, say, one mole of 1,5-dibromo-pentane with excess ammonia in ethanol can result in the formation of rings. (e.g. $1\lambda^2$-piperidine) However, it is also possible for the 1,5-dibromo-...
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1answer
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Reagents in Krapcho's decarboxylation

Krapcho's decarboxylation is a reaction involving esters with a electron-withdrawing group $\beta$ to the carbonyl group and halide ions. It is typically conducted with $\ce {LiCl}$ and $\ce {DMSO}$ ...
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1answer
103 views

Nucleophillic addition vs SN2

The following question came in Paper 2 of JEE Advanced 2014- Here we have $\ce{CH3-}$ as the nucleophile. There are 2 possible attacks: SN2 type attack on the chlorine group. Nucleophilic addition ...
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Reactivity of primary and tertiary alkyl halides

From USNCO 2004, Q58: The reaction between which pair of reactants occurs the fastest for $[\ce{OH-}] = \pu{0.010 M}$? (A) $\ce{CH3CH2CH2CH2Cl + OH-}$ (B) $\ce{(CH3)3CCl + OH-}$ (C) $...
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Alcohol or Carbonyl - Which is more reactive towards PCl5?

We're aware that ketones and alcohols both react with phosphorus pentachloride, to produce geminal dichlorides and alkyl chlorides respectively. What happens in the compound shown below, when ...
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1answer
400 views

Order of reactivity of nucleophilic addition at carbonyl group with Grignard reagent

I thought the order would be $1 > 3 > 2$ as 1 is aldehyde and 2, 3 are ketones. As generally aldehydes are more reactive, I placed it first. I chose 3 over 2 as two alkyl groups would make ...
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1answer
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Why can't you form an anhydride from an ester via nucleophilic attack?

The reaction referred to is the nucleophilic acyl substitution reaction, where the nucleophile is a carboxylate ion and the electrophile is the ester. I am having a difficult time visualizing why this ...
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Charge distributions in the transition state of the SN2 reaction

I understand that a similar question has been posed here. However, the scope of my question is framed differently. I will present analysis of two different sources of information and I would like to ...
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147 views

Effect of solvent polarity on SN1 reactions of different charge types

On the topic of the ionisation mechanism (i.e. $\mathrm{S_N1}$), Carey & Sundberg (2007) discuss the effect of polarity of solvent on the rate of $\mathrm{S_N1}$ reactions of different charge ...
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Dependence of rates of neighbouring group participation on length of alkyl chain

On the topic on neigbouring group participation, it is mentioned in Carey & Sundberg (2007)[1] that the effectiveness of the participation is dependent on on the ease with which the molecular ...
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2answers
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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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3answers
248 views

Why does using NaI as a nucleophile and acetone as solvent lead to an SN2 reaction mechanism instead of SN1? Is I- not considered a weak nucleophile?

In a reaction with a secondary leaving group, why does using $\ce{NaI}$ with acetone as a solvent lead to an $\mathrm{S_N2}$ reaction mechanism instead of $\mathrm{S_N1}$? I thought that halogens were ...
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2answers
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Addition reaction(Haloalkane) [closed]

In these reactions if two reagent is given how to decide who is going to react with the compound.HBr is a strong acid CH3OH is a weak base.So HBr dissociate easily but CH3OH is reacting with the given ...
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1answer
85 views

Displacement of leaving groups in organic reactions

When I initially learned about substitution reactions, there would be times where a poor leaving group had to be changed into a better one in order to proceed with a substitution reaction. For ...
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1answer
64 views

Do bulky bases participate in substitution reactions?

I see how bulky bases influence the regioselectivity of E2 and E1 reactions. I do not see very much content on the involvement of bulky bases in substitution reactions. I know that bulky bases like t-...
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1answer
170 views

Electronic effects of substituents in the benzyne mechanism

On the topic of nucleophilic aromatic substitution (S$_N$Ar) reactions, the benzyne mechanism is discussed. When considering the position of substitution, electronic and steric factors are mentioned. ...
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153 views

Converting a thioester to an amide

What reagents can I use for the following transformation? I think this has something to do with formation of an iminium salt and reductive amination, but I'm not so sure.
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How does ring size affect SN2 reactions?

Suppose we have to compare the $\mathrm{S_N2}$ reactivity order for cyclopropyl and cyclopentyl chloride. How can we do that? I think that cyclopentyl should be more reactive towards $\mathrm{S_N2}$ ...
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1answer
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Why do *tert*-butyl ethers in diluted sulfuric acid undergo elimation instead of solvolysis?

My organic textbook states the pathway for propyl tert-butyl ether in dilute sulfuric acid will follow E1 with a tertiary carbocation intermediate. It mentions that Sn1 will only occur with good ...
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1answer
306 views

Rearrangement with sodium iodide (ring opening)

I'm not able to figure out the mechanism for this reaction. I don't see how sodium iodide in acetone could lead to rearrangement, and surprisingly ring opening! What is this reaction called, if it ...
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0answers
456 views

What are the partial charges in an SN2 transition state?

What are the partial charges of on the atoms in a SN2 reaction? The nucleophile is normally negatively charged and has a lone pair of electrons. This would make you think the transition state would ...
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1answer
227 views

Organic reaction with Na2S2O4 [closed]

Question: In the first step due to cooperating Inductive and resonance effect C6H5N2 + will be attached at the ortho position of methyl group for which para position is occupied by Amine group ...
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Why ammonium salts can not undergo substitution

Why is ammonium salt, such as RNH3+, can not react with nucleophiles like HI to give RI and NH4+? The reaction is pretty much like the substitution of alcohol in acid condition. In my opinion, NH3 (...