Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: betterbesafehero on April 30, 2013, 09:10:59 AM
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Does it happen only in cyclic compounds ?
What are the circumstances in which it really happens ?
Give me 2 or 3 picture examples of reactions in which intramolecular substitution is taking place.
And lastly which mechanism does it follow, SN1 or SN2 or both depending on the compound ?
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I don't know quite what to make of this question. What inspires you to ask this?
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I don't know quite what to make of this question. What inspires you to ask this?
I am a aspiring student of competitive examination named IIT-JEE for undergraduate studies. These type of questions are sometime asked. I have read many books but couldn't really found the examples of Intramolecular Substitution. If anyone knows about this, I would be really thankful to you to answer all my queries and doubts.
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The short version is that there's a lot of variations on intramolecular substitutions, they tend to be ring-forming starting from an open chain although there are exceptions.
Look up epoxide formation from a halohydrin, that's a good simple example.
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Please provide me with all the answers of questions I asked.
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Please provide me with all the answers of questions I asked.
Please read the forum rules (http://www.chemicalforums.com/index.php?topic=65859.0). You have to show your attempts at solving the question to receive help. This is a forum policy.
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Please provide me with all the answers of questions I asked.
I'm guessing you didn't know this, as I don't think English is your first language, but this comes across as an extremely rude response to an answer which would have put you on the right track.
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Please provide me with all the answers of questions I asked.
Please read the forum rules (http://www.chemicalforums.com/index.php?topic=65859.0). You have to show your attempts at solving the question to receive help. This is a forum policy.
I am not asking problem. This is not a problem I am asking. I am asking for help in mechanism, and in which circumstances does it really happen. In short I am asking to elaborate a simple and short topic of organic chemistry.
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Like this one. I think in this intramolecular substitution is taking place.
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Please provide me with all the answers of questions I asked.
I'm guessing you didn't know this, as I don't think English is your first language, but this comes across as an extremely rude response to an answer which would have put you on the right track.
Okay then sorry..!
Please if you would help me with all the questions I asked, I would be really grateful. I know about Intramolecular Substitution. I read that reaction and mechanism of epoxide formation from a halohydrin. I understood that.
Sorry again.
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What are the circumstances in which it really happens ?
How am I supposed to know that intermolecular substitution is going to take place? This is what I really want to know.
Like SN1: favored by polar protic solvent, and higher degree of alkyl hallide
and SN2: favored by polar aprotic, lower degree of alkyl hallide, less hindered carbon.
I am not being rude or abrasive. I apologize to every one of you. Maybe I want my answer fast, I have to study, just don't have much time. I am really sorry.
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Okay, no worries. To answer your question, the last example you posted (the cyclohexane derivative with base) is definitely an intramolecular substitution, and it is definitely an Sn2 reaction as it is driven by a strong (thiolate) nucleophile. I noticed that discussion of the nucleophile wasn't included in your list of factors that distinguish Sn1 and Sn2 reactions, and nucleophile is possibly the most important factor, so you might want to review those.
My organic chem instructor put it like this: he told everyone in the class to touch their head with their right hand. Then he told them to touch someone else's head with their right hand. After everyone got done laughing and falling over, he pointed out how much easier it was to touch your own head - the "intramolecular" reaction. Because the molecule's backbone holds the two reacting groups close to each other, intramolecular reactions will almost always be faster unless the resulting ring would be very strained, and sometimes even then it is okay.
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^^^Yes nucleophile plays an important role in substitution reactions. Okay I understood why it happens and it would be faster, try helping me with all the questions.
Can you cite few examples to elaborate the concept of this substitution.
and when it is favored, like which conditions favor intramolecular substitution ?
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Any time you have a choice between intramolecular reaction ("cyclization") and intermolecular reaction ("condensation") the intramolecular one is likely to dominate unless there is some strong other reason it wouldn't, like for instance if intramolecular reaction would make a very strained ring.
For instance, look at page 5 here:
http://www.faculty.umassd.edu/xtras/catls/resources/binarydoc/2437.pdf
That's a classic SN2 reaction and it could take place intramolecularly as shown, or intermolecularly making an amine polymer. However, the intramolecular reaction is dominant.
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So I guess it is due to ring strain that the yield is 5% ?
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Should I assume that intramolecular substitution always result in cyclization and would always go by SN2 mechanism as good nucleophile is required to initiate it ?
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Is it Intramolecular SN1 ?
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Yes, this is a good example of an intramolecular SN1 reaction.
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Please answer this 'Should I assume that intramolecular substitution always result in cyclization' ?