Questions tagged [nucleophilic-substitution]

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

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26
votes
3answers
7k views

Explanation for the trends in nucleophilicity—Orbital interactions or electrostatic attraction

The trend of halide nucleophilicity in polar protic solvents is $$\ce{I- > Br- > Cl- > F-}$$ The reasons given by Solomons and Fryhle[1], and by Wade[2] are basically as follows. Smaller ...
37
votes
5answers
41k views

Why does alcoholic KOH prefer elimination whereas aqueous KOH prefers substitution?

What is the basic difference between aqueous and alcoholic $\ce{KOH}$? Why does alcoholic $\ce{KOH}$ prefer elimination whereas aqueous $\ce{KOH}$ prefers substitution?
5
votes
1answer
525 views

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 ...
40
votes
2answers
56k views

Why do SN1 and SN2 reactions not occur at sp2 centres?

I was told in my organic chemistry course that $\text{S}_\text{N}1$ and $\text{S}_\text{N}2$ reactions did not occur at $\text{sp}^2$ centres. When I asked why, I was not given a satisfactory ...
26
votes
2answers
14k views

Why do we get slightly more inversion product than retention product in SN1 reaction?

Theoretically, in $\mathrm{S_N1}$ reaction we should get a racemic mixture as the product because the nucleophile can attack from either side of the formed carbocation. However, many textbooks claim ...
11
votes
1answer
2k views

Order of halide nucleophilicity in DMF

The order of nucleophilicity for halide family in DMF is: $\ce{Cl- > Br- > I-}$. I understand the reason for this must be that DMF, being a polar aprotic solvent, is unable to solvate the ...
8
votes
1answer
1k views

How to rationalise the major product formed in a nucleophile promoted epoxide cleavage reaction?

The Problem is to find major product of reaction as given below (the star is a labelled carbon): The two possible reactions that come to my mind are: Nucleophile promoted epoxide cleavage reaction, ①...
7
votes
1answer
342 views

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 ...
14
votes
3answers
8k views

Comparing SN2 reaction rates

I've read in a book that the main factor for determining SN2 reaction rate is steric hindrance. The lesser it is, the faster the reaction. So consider this question: $\ce{KI}$ in acetone undergoes ...
12
votes
2answers
9k views

Why are alpha carbonyl halides most reactive towards SN2 reactions? [duplicate]

Relative rates of some compounds towards SN2 is given below The reason for reactivity of alpha carbonyl halides is given as It’s not clear what exactly is happening.
7
votes
5answers
40k views

How does the inductive effect, explain the reactivity of tertiary alcohols with halogen acids?

The reactions of primary and secondary alcohols with halogen acids ($\ce{HX}$, where $\ce{X}$=halogen) require the presence of a catalyst, $\ce{ZnCl_2}$. With tertiary alcohols, the reaction is ...
4
votes
0answers
905 views

Comparison of the rate of SN1 and SN2 reaction

It is known that $\mathrm{S_N1}$ (Substitution Nucleophilic Unimolecular) follows the order of rate of reaction: Tertiary ($3^\circ$) > Secondary ($2^\circ$) > Primary ($1^\circ$) For $\mathrm{...
8
votes
1answer
954 views

Rates of solvolysis of p-dimethylamino benzyl halides

What will be the order of $\mathrm{S_N1}$ solvolysis rates for these? I'm confused between the second and third options. $\ce{I-}$ is a better leaving group than $\ce{Br-}$, but the carbocation ...
0
votes
1answer
146 views

Why is Finkelstein reaction not conducted using NaF?

I was studying the Finkelstein reaction and all sources through which I have studied this reaction indicate that the reaction uses $\ce{NaI},$ where $\ce{I-}$ acts as the nucleophile which will then ...
20
votes
1answer
8k views

Ipso substitution and its rules

I was taught that the following reaction happens: It is called the "ipso-substitution". My professor had told me that it occurs in the case of $\ce{-SO3H}$ and $\ce{-COOH}$. But he had ended the ...
10
votes
1answer
689 views

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 ...
8
votes
1answer
226 views

Can NaH open the epoxide ring to form alcohol? If so, how?

I was looking at the organic chemistry 8th Ed textbook by Paula Yurknais Brucie. On page 509, I found this: I think about it for a while and I am doubting that it is wrong. I believe the hydride ion ...
8
votes
1answer
1k views

What is the reaction mechanism of nitrogen leaving from diazo compounds?

When a diazo compound is formed, and then a nucleophile is added to the mixture. Will nitrogen gas leave first or will the nucleophile have to "do" a substitution reaction? What I mean is will the ...
7
votes
2answers
280 views

Proton removal during benzyne formation in substituted haloarenes

I encountered the following question in an organic chemistry paper - The reaction follows benzyne mechanism. My answer was B. However, the answer given in the test solutions was D. The mechanism ...
2
votes
1answer
859 views

Does the reaction of 1-bromobutane with cyanide ion follow an SN1 or SN2 mechanism?

In my textbook it's mentioned that the reaction undergoes $\mathrm{S_N2}$ mechanism. I understand that the carbon attached to the bromine is primary, but both solvents here are polar protic solvents, ...
2
votes
1answer
6k views

How can aqueous KOH give alcohol by SN2 of alkyl halide?

I ask this because SN2 requires a strong nucleophile, and I have read $\ce{OH-}$ isn't a strong nucleophile in a polar protic solvent like water. So, how can $\ce{OH-}$ replace, say $\ce{I-}$ from $\...
1
vote
1answer
1k views

How to be able to tell if a molecule will react via SN1 or SN2?

I've been having a lot of issues with a question. 2 compounds, (1-chloro-2,2-dimethylpropyl)benzene and (1-chloro-2-methylpropyl)benzene react with EtOH in water. It asks to classify the reaction ...
8
votes
2answers
4k views

SN1 reactivity order

The question is to compare the SN1 reactivity for the following compounds. According to me it should be like R>S>Q>P. But the correct answer is Q>P>R>S. How can a lone pair donating into a vacant p ...
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? ...
2
votes
1answer
2k views

SN1, SN2 or acid-base reaction

I am asked to give the type of reaction (SN1, SN2 or acid-base reaction) for the following reactions. I know that both $\ce{MeOH}$ and $\ce{EtOH}$ polar protic solvents, so because the first is an SN2 ...
2
votes
1answer
291 views

How to explain the selectivity between methanol and methanethiol in an SN1 reaction with an halogenated hydrocarbon?

Consider the SN1 reaction shown below: Would different products be formed if $\ce{CH3SH}$ was an additional reagent? Superimpose both energy diagrams on top of each other. For the first question, ...
12
votes
4answers
9k views

Will this beta-branched secondary alkyl halide undergo SN1 or SN2?

What is the correct mechanism here? Would SN1 occur here? I chose SN2 because we have a secondary alkyl halide with a weak base $\ce{CN-}$. However, the solution says SN1 is major. Can you explain ...
7
votes
1answer
1k views

Can an SN1 reaction occur in compounds with the leaving group attached to a primary carbon, which can later rearrange?

Can SN1 reactions occur in compounds where the carbocation, even though is is initially $1^\circ$, can rearrange to form a more stable carbocation? Examples cases:
5
votes
2answers
1k views

Does halogenation by phosphorus tribromide lead to an inverted product?

I think it follows the SNi mechanism and would not lead to Walden inversion. Hence, the product should be (S)‐2‐bromobutane: But the answer says otherwise (the problem didn't indicate the presence of ...
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
1answer
3k views

Effect of solvent in the reaction of alkyl halide with nitrite ion

$$\ce{RX + NaNO2 -> ?}$$ Is there a difference in the outcome of the reaction if the solvent is changed from an alcohol (e.g. EtOH) to a polar aprotic solvent such as DMSO or DMF? I have two ...
5
votes
1answer
224 views

Steric effect of t-butyl group on SN1 on a cyclohexane ring

This is a question from GRB Kota Question Bank Organic Chemistry, Chapter 3, Reasoning type, Q. 4: Assertion: trans-1-t-butyl-4-chlorocyclohexane is less reactive than cis-1-t-butyl-4-...
4
votes
1answer
309 views

Mechanism for the reaction between trisilylamine and hydrogen chloride

In Concise Inorganic Chemistry by J. D. Lee (adapted by Sudarsan Guha), in the chapter "Chemical Bonding", under the topic "Back Bonding with Nitrogen as a donor atom" the following reaction is given: ...
3
votes
0answers
2k 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 ...
3
votes
0answers
103 views

Nucleophilic substitution in aromatic compounds

Predict the major product in following reaction: In my view this reaction will proceed via benzyne intermediate and $\ce{NH2-}$ will act as a base and substitute one of the chlorine. After benzyne ...
3
votes
1answer
802 views

Why do some nucleophiles attack at the carbonyl group while others at an alpha-carbon in ketones?

I was reading about the iodoform reaction and it stated that $\ce{OH^-}$ attacks at the $\alpha$-carbon and makes a substitution reaction possible. But there is also the possibility of attacking the ...
2
votes
1answer
407 views

Confusion about the SN1 and SN2 Mechanism

My book says, and I understand, that the $\mathrm{S_N1}$ mechanism is much faster for tertiary alkyl halides than primary. And the opposite for $\mathrm{S_N2}.$ This all makes sense. What I don't get ...
2
votes
1answer
890 views

Why do polarizable nucleophiles favor SN2 over E2?

Weakly basic ions and polarizable bases favor $\mathrm{S_{N}2}$ over $\mathrm{E2}$. Why? The argument used that polarizable nucleophiles form bonds earlier, stabilizing the transition state, can be ...
1
vote
1answer
645 views

Which mechanism do ethers follow when cleaved by hydrogen halides?

Ethers can be cleaved under acidic conditions by treatment with hydrogen halides (HX, where X = Cl/Br/I). Some of these reactions proceed by SN1 mechanisms and some by SN2 mechanisms. How can I tell ...
1
vote
1answer
1k views

How to determine if a reaction proceeds via SN1, SN2, E1 or E2 mechanism?

Give the main product and reaction type: SN1, SN2, E1 , E2. As the 1-bromohexane is primary and the nucleophile a strong unhindered base, the reaction should be a SN2 reaction. However, the solvent $...
0
votes
1answer
77 views

Are the reaction rates of these equations equal? [closed]

$$\ce{CH3CH2CH2Br + OH- -> CH3CH2CH2OH + Br-}$$ $$\mathrm{rate} = k[\ce{CH3CH2CH2Br}][\ce{OH-}]$$ If I change the $\ce{Br}$ with any element from halogens (without changing concentration, volume, ...
0
votes
0answers
410 views

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 ...
-1
votes
1answer
536 views

Comparing reactivity of 1-chloroethane and 1-chloropropane in an SN1 reaction

Beginning with a reference to a well known question. Order by reactivity towards SN1 reaction. According to some facts about SN1 reactions, rate depends on: Stability of carbocations Better leaving ...
-2
votes
1answer
1k views

Rate of formation of hydrate in a carbonyl compound [closed]

When water in presence of any acid is added to a carbonyl compound, it leads to the formation of its hydrate. But how do we determine the rate of reaction? Is it done by checking the amount of partial ...