If you didnt know whether the reaction was Sn1 or Sn2, what physical property could you use to distinguish them? But I am little bit confused in trend of nucleophilisity of halogens in polar aprotic solvents. Thank you.
Even with the help given, I am having trouble with how kinetics can be used to tell the difference between SN1 and SN2. Double the concentration of substrate and double the concentration of nucleophile. If the reaction is first order overall, the reaction rate will only double.
If the reaction rate is second order overall, the reaction rate will quadruple. Thank you! What about the effect of the polar aprotic solvent on the rate of rxn? SN1 mechanism — the rate of reaction depends on substract. It is independent of nucleophile. So it can show ist order mechanism unimolecular. It is more than 1 step mech. Most stable carbo cation will favour sn1 mech. Polar protic solvent will favour Best solvolysis can favour More steric hindered can show sn1 mech. I know primary substrates favor SN2 and E2 reactions — but my book talks about how a primary carbocation can form in an SN1 reaction if it is accompanied by a simultaneous rearrangment.
The book specifically says it can happen as a result of a methyl shift. My question is: can it also happen via a simultaneous hydride shift? Or only through a methyl shift? My teacher has given us some problems to work through that would require a primary carbocation to form through a hydride shift, and I just want to make sure that is feasible.
Thank you very much for your views regarding the Sn1 and Sn2 reaction…….. This will help me alot….. Good explanation. Specially the story of the cats and the relation with the reactions is very good. Just wanna say that I already bought all your cheat sheets and it is a big help!! Thank you for clear explanations :. This is very impressive.
In applied organic chemistry. And it helped me to explain this to my students. The cat example is nice. Is it possible a trans compound react in a SN2 reaction? How do we know if its possible to have the mixture of the 2 configurations? With cyclohexanes, the important thing to note is that the leaving group must be axial in order for the SN2 to occur. Also love the summary sheet for this subject, super helpful as well.
Wonderfully describe. I am a chemistry teacher; I teach that topic to my students as per your article. I like your way of understanding. Thank you so much for sharing your this information about two reactions. Why reactivity in SN1 reaction is directly proportional to the on stability of carbonation? And how? Please respond me. What should i do when both strong and weak nucleophile are present in the reaction???
If the substrate is primary, it will be SN2, since the reaction rate will be faster with a stronger nucleophile. Hi,thanks for the post. But here is question. In SN1 reactions the rate limiting step is loss of leaving group to give a carbocation. If a more stable carbocation can be formed through a hydride or alkyl shift, do this rearrangement first! The third case — addition of H2SO4 to a tertiary alcohol — is a case where a carbocation is formed in the absence of a good nucleophile [the negatively charged oxygen on the conjugate base, [HSO4 - ] is stabilized through resonance, reducing its reactivity].
The fact that heat is being applied helps to tip the balance even further toward E1 being dominant over SN1. In the fourth example we have a tertiary halide [which will form a stable carbocation] in a polar protic solvent [will help to stabilize the intermediate carbocation] and heat is not indicated. It is not applied evenly and there are plenty of exceptions. Your mileage will vary widely. I wish I had a hard, concrete example to show you that clearly demonstrates the relationship between increased heat and a greater proportion of elimination E1 versus substitution SN1 products.
Sadly, I cannot find a good example at this time. I would love to see the control experiments with various substrates run under identical sets of conditions that clearly delineate the impact of each variable. I have not seen this. Any undergraduate labs out there with a desire for performing this valuable public service? The post above is not so much about understanding some facet of organic chemistry as it is about how to answer some arbitrary question from a textbook or exam.
For the purpose of knowing how to answer a particular kind of question on an exam, it will of course depend on the examiner.
There are wide variations. First, background. However, on an exam , instructors — for various reasons, including a well-intentioned desire not to overwhelm the student — will often omit some of the data.
For exam purposes, if the above reaction were written as a question it will often look like this:. This is because the better leaving group leaves faster and thus the reaction can proceed faster. Other examples of good leaving groups are sulfur derivatives such as methyl sulfate ion and other sulfonate ions See Figure below.
Reaction proceeds via SN1 because a tertiary carbocation was formed, the solvent is polar protic and Br- is a good leaving group. This reaction occurs via SN1 because Cl- is a good leaving group and the solvent is polar protic.
This is an example of a solvolysis reaction because the nucleophile is also the solvent. Just as with S N 2 reactions, the nucleophile, solvent and leaving group also affect S N 1 Unimolecular Nucleophilic Substitution reactions. Polar protic solvents have a hydrogen atom attached to an electronegative atom so the hydrogen is highly polarized. Polar aprotic solvents have a dipole moment, but their hydrogen is not highly polarized.
Polar aprotic solvents are not used in S N 1 reactions because some of them can react with the carbocation intermediate and give you an unwanted product. Rather, polar protic solvents are preferred. How does polarity affect SN1 reactions? How does temperature affect SN1 and SN2 reactions? What conditions favour nucleophilic substitution? Why is acetone used in SN2 reactions?
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