23
votes
Why do we get slightly more inversion product than retention product in SN1 reaction?
It is well known that SN1 reactions often give incomplete racemisation:
Although many first-order substitutions do give complete racemization, many others do not. Typically there is 5–20% inversion, ...
- 17.1k
19
votes
Why do we get slightly more inversion product than retention product in SN1 reaction?
As we know, $\ce{S_N1}$ reaction is stereochemically non specific. This means, that it does not force the formation of one stereoisomer, as $\ce{S_N2}$ does. In $\ce{S_N1}$ reaction, presence of ...
- 5,647
19
votes
Accepted
Explanation for the trends in nucleophilicity—Orbital interactions or electrostatic attraction
This is a rather intellectually-stimulating question and one that is also very difficult to answer. You have constructed a very good case for why the nucleophilicity order would not be expected to ...
- 10.2k
17
votes
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Are nucleophilic substitutions reversible?
In general, yes, $\mathrm{S_N2}$ reactions are reversible. But not in this particular case.
Rates of $\mathrm{S_N2}$ reactions depend on several factors: the nucleophile, the leaving group, the alkyl ...
- 71.1k
14
votes
What are SN1ʹ and SN2ʹ reactions?
The primed version of $\mathrm{S_N1}$ and $\mathrm{S_N2}$ can only occur if there is a double bond in the vicinity of the leaving group as in your example. I have drawn both possibilities for the $\...
- 67.3k
14
votes
Ipso substitution and its rules
The shorthand way that we draw structures in organic chemistry, with implicit hydrogens, leads us to often forget that the hydrogens are there, or to neglect considering them in our analyses. In ...
13
votes
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Rates of solvolysis of p-dimethylamino benzyl halides
In the second compound, steric repulsions (denoted by the curly lines) between the N-methyl groups and the methyl groups on the ring occur:
This forces the $\ce{-NMe2}$ group to rotate such that the ...
- 71.1k
13
votes
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Rearrangement with sodium iodide (ring opening)
I think the final product will also contain some Bromine atoms attached to it. and the no. of double bonds will be one less than that of the compound given in the picture. I may be wrong but with all ...
- 5,593
12
votes
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Does halogenation by phosphorus tribromide lead to an inverted product?
Yes, the haloalkane product will have the inverse stereochemistry of the alcohol that it was produced form. $\ce{PBr3}$ does this by converting the $\ce{-OH}$ into a good leaving group and providing a ...
- 23.9k
12
votes
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Why do SN1 and SN2 reactions not occur at sp2 centres?
Not a bad question, but a poor answer. The person who mentioned $\mathrm{S_N2}$' is on a much better track.
Nucleophilic attack on a carbonyl or 1,4-Michael acceptor is not an $\mathrm{S_N2}$ ...
- 136
12
votes
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The reaction of Alkyl Halides with sodium nitrite in DMF
The $\mathrm{S_N1}$ or $\mathrm{S_N2}$ reaction of alkyl halide with nitrite ion is complicated one since nitrite is an ambident nucleophile. For instance, it was reported that silver nitrite reacts ...
- 39.5k
10
votes
Does the reaction of 1-bromobutane with cyanide ion follow an SN1 or SN2 mechanism?
Agreed, $ \ce{Br-} $ is a good leaving group, so one would expect that an SN1 mechanism is not too difficult to have in a polar protic solvent. But do not forget that the mechanism of any reaction is ...
- 333
10
votes
Why are alpha carbonyl halides most reactive towards SN2 reactions?
I have asked a question previously which concerns the same electrophilic system with the exception that nucleophilic attack happens on the carbonyl carbon and not on the α-carbon.
From the organic ...
- 67.3k
10
votes
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Alcohol or Carbonyl - Which is more reactive towards PCl5?
Reaction of alcohols with PCl5 and PCl3 (for reaction with alcohol)
Mechanism for conversion of ketone to dichloride with phosphorus pentachloride
(for reaction with ketone)
Now as per the question as ...
- 744
10
votes
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Why does this ring contraction take place in the following nucleophilic substitution?
This reaction should be leaning towards SN1 because the approach of $\ce{H2O}$ for a back attack to the ABMO of the $\ce{C-Br}$ is heavily hindered since the neighborhood is congested due to the small ...
- 1,514
10
votes
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Can NaH open the epoxide ring to form alcohol? If so, how?
Further to my comments above, I am going to offer my opinion that the book is wrong and the epoxide is not opened by sodium hydride as depicted. I have failed to find any literature examples of such a ...
- 21.6k
9
votes
Why is pyrrole more reactive than pyridine and benzene for an electrophilic substitution reaction?
From Peter Sykes:
Pyridine (62), like benzene, has six at electrons (one being supplied bynitrogen) in delocalised it orbitals but, unlike benzene, the orbitals will be
deformed by being ...
- 5,504
9
votes
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How does ring size affect SN2 reactions?
TL;DR - Bond angle strain gets a lot worse in going from cyclpropyl chloride to the transition state for the 3-membered ring example, than for cyclopentyl chloride going to the corresponding ...
9
votes
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Reaction of phenol with phosphorus tribromide
TL;DR: It is a possible but complicated reaction and you get a mixture of products but formation of haloarene is not significant in any reaction
Long answer:
phosphorus trichloride: form triphenyl ...
- 25.2k
8
votes
Why does alcoholic KOH prefer elimination whereas aqueous KOH prefers substitution?
The reason is quite straightforward-
$\ce{OH^-}$ is a weak base and a stronger nucleophile specially under polar protic conditions. Hence substitution occurs.
$\ce{RO^-}$ is a strong base owing to ...
- 73
8
votes
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How to rationalise the major product formed in a nucleophile promoted epoxide cleavage reaction?
Let's do this step by step and figure your questions out.
First, what a nucleophile needs is positive terminal in the compound.
The other carbon attached to oxygen is not as positive as the one where ...
- 1,234
8
votes
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Mechanism for the conversion of an unsaturated alkyl halide to an alcohol
For what it's worth, this reaction does not appear in the literature. So, whether it actually forms the product or not is anybody's guess.
However, if I had to suggest a mechanism... I would note ...
- 71.1k
8
votes
The effect of the groups at para position on SN2 reactivity
This is what I found from your reference to Clayden. You just had to read the next paragraph ( I have highlighted the point ). You can see that March and Clayden have agreed on the same point, that ...
- 423
8
votes
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Regioselectivity in iodolactonisation of γ,δ-unsaturated carboxylic acid
There are several arguments. Firstly, five-membered ring formation is generally kinetically more favourable than 6-membered ring formation. As ring size increases, the entropy of activation also ...
- 71.1k
8
votes
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What would the following NGP reaction yield?
Reaction-1 is a simple example of an $\mathrm{S_N2}$ reaction, where the acetate group ($\ce{AcO-}$) substitutes the tosyl group ($\ce{OTs}$) forming the product (1) as follows:
But for Reaction-2, ...
- 3,186
8
votes
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Steric effect of t-butyl group on SN1 on a cyclohexane ring
I would argue that the reasoning makes sense.
There are some important things to discuss here.
The cis isomer ($C$) and the trans isomer ($T$) will both react via the same carbocation intermediate. ...
- 17.3k
8
votes
What is the mechanism for this intramolecular SN1 reaction?
You are correct on your initial assumption. This hydrolysis is assisted by the neighboring thiomethoxy group ($\ce{SCH3}$) as depicted in the following scheme:
The cyclic methylsulfonium intermediate,...
- 39.5k
8
votes
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Reaction of cyclohexene oxide with LDA
Because of the steric hindrance of the two iPr groups, LDA is a very poor nucleophile. It is, as you note, a very strong base. The two products observed both arise from deprotonation of cyclohexene ...
- 21.6k
8
votes
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What is the correct reaction mechanism?
I see what went wrong. Such questions are often confused with aldol or cannizarro as they have a carbonyl group and a base is given.
Actually this is a completely different name reaction called ...
- 445
7
votes
Do alcohols react with alkyl halides?
I am assuming that you want the alcohol to react with the $\ce{OH}$ group and the alkyl halides to react with the $\ce{Cl}$ group.
Both groups like to withdraw electrons, so they tend to be negative, ...
- 5,005
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