Here comes James, frighten the poor hobo away so he can seat himself on the bench. James must be big and intimidating. It is and thanks for making it comprehensible. I v already covered this with my students but I ll use this to refresh them again. Some of my students challenged me to do the upcoming class in haiku. Since a fractonal distillation lab is pretty dull to supervise after everyone is up and running, I put the introduction to SN1 in haiku format.
Each done on a powerpoint slide with a pretty background…. Hey, just a question here. I do know that branching of the substrate helps stabilize the carbocation…. Lets think about the carbocation during its transition state. It positively charged and thus in an ideal world it would want to be stabilised, thus reducing its energy. If you have large bases this can almost protect the transition state, providing mixed effects with the stabilisation of the cation being good, the steric hindrance for the nucelophile being bad.
Allylic system are more reactive becoz of resonance for which there must be formal charge intermediate as in SN1 not SN2. So why is it that without any charged intermediate the left bromine is favored. This was so outrageously helpful. I will definitely be using this site for much of my orgo work this year. Wow — such a good website and so well explained thank you sooooo much. Way better then my lectures :. Sir Thank you, I was looking for this article.
Sir will you please explain me why alpha-halocarbonyl compounds are not much reactive with Sn1 mechanism? If you guys are confused about rate determining steps, I would encourage reading that chapter or review it thoroughly. I will try to explain it here a little. Since the rate determining steps depend on the carbocations, so we look at 1st order kinectic , which can be found by.
So as the both increases the reaction rate will go up, if one goes down, it is kind of like limited reagents , which one exhaust first etc, if one is exhausted, does not matter, how much you have the other, the reaction WILL NOT Proceed. I wanted to check the exercises pointed out at the end of this lecture, but the link gives an error — File or directory not found.
Thank you so much for the nice explanations. Your explanations helped me get several difficult points cleared. Thanks for the great explanation. I have a question about the rate of Sn1 reaction, how would a primary carbocation that can undergo an alkyl shift to become tertiary fit in, I know that a primary carbocation is slower than secondary, but the shift would stabilize it.
If talking about the rate of formation of a free carbocation, formation of primary carbocations is slower than that of secondary. That makes it difficult to strictly compare the rates since they occur through different mechanisms. Am a student taking organic chemistry at Kenyatta University-Kenya, this is so helpful to me Thank You so much. This is absolutely wonderful resource! Thank you so much. Love this piece of text…. Hello, I have a question about steric hindrance for an Sn2 reaction.
Specifically with cycloalkanes. I thought that the higher the number of carbons a cycloalkane has the more corners it has the more likely it was for a nucleofile to attack it from the inside. And it puts Cyclopentane more reactive before Cyclohexane. Many thanks in advance! Love your website! Hard to say re: cyclopentane vs. Could it have something to do with angle strain? The stability of the tertiary carbon allows it to be a stronger carbocation compared to primary carbon which is very unstable as it the carbocation formed would be unstable.
So reactivity of SN1 reaction increases as the groups around carbon increase. This in turn renders the cation strong enough to react with a weak nucleophile. This analogy is fab…Its so clever and easy to remember! Thank you so much…I made use of it in my oxford interview! It is very un-PC to be using homeless people in this analogy, imagine if you changed the analogy to a black person on the bench and a white person wanting to sit down quite offensive.
You have a cartoon of two cats wanting to sit in a basket, why not just use that analogy; how about just two people, one sitting on the bench and the other wanting to sit on the bench, no socio economic issues implied. Apart form that very useful information.
Thanks for this great explanation! 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.
If we had a strong nucleophile generally, a strong nucleophile is negatively charged then it will be able to react with the substrate and neutralize the positive charge, but the problem arises when considering the negative charge on the leaving group.
How can it neutralize its charge? A weak nucleophile is neutral, so when it reacts with the substrate, the positive charge doesn't get neutralized. Instead, the positive charge jumps onto the newly attached nucleophile and the leaving group is able to neutralize itself usually by pulling off a proton.
This gets rid of both the negative charge on the leaving group and the positive charge on the newly attached nuc. Dan Retired Staff Sr. Quote from: ariaxxx on July 01, , AM.
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