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Topic: Explain reaction of propene with Cl2 and H2O please  (Read 3478 times)

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Offline carotis

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Explain reaction of propene with Cl2 and H2O please
« on: September 12, 2016, 12:17:03 AM »
Hello, folks! It's faily standard stuff, I am aware of it but I have problems to properly explain whyx in the recation of Cl2 and H2O with Propene results into 1-Chloro-2-propanol and not for example 2-chloro-propanol. Someone can clarify this pretty please?

Offline AWK

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Re: Explain reaction of propene with Cl2 and H2O please
« Reply #1 on: September 12, 2016, 12:33:55 AM »
H2O + Cl2 =
AWK

Offline Vidya

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Re: Explain reaction of propene with Cl2 and H2O please
« Reply #2 on: September 12, 2016, 01:10:06 AM »
Hello, folks! It's faily standard stuff, I am aware of it but I have problems to properly explain whyx in the recation of Cl2 and H2O with Propene results into 1-Chloro-2-propanol and not for example 2-chloro-propanol. Someone can clarify this pretty please?
I tell you how to understand this reaction with the help of your text book ..
First try to understand the nature of double bond in alkene ..Is it considered as electron rich site or poor site ....how pi bond will break in the presence of an electrophile ...analyze which carbon around the double bond will get the positive charge (review stability of carbocations to identify carbon with positive charge )..now check which one is electrophile and which one is nucleophile to know which carbon will get Cl and which carbon will get OH ..in this reaction Cl is the electrophile and water is the nucleophile ...
You need to understand the mechanism of the reaction with the stability of the carbocation ...

Offline Enthalpy

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Re: Explain reaction of propene with Cl2 and H2O please
« Reply #3 on: September 15, 2016, 06:13:37 PM »

Offline Babcock_Hall

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Re: Explain reaction of propene with Cl2 and H2O please
« Reply #4 on: September 16, 2016, 10:57:53 AM »
@OP, What is the intermediate in this reaction?

Offline carotis

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Re: Explain reaction of propene with Cl2 and H2O please
« Reply #5 on: September 28, 2016, 11:58:14 PM »
"chloronium cation"  ;D Depending on which C bons how many H, there is a electrophilic and nucleophilic area, which reacts perceptivly with the more nucleophilic or electrophilic atom.

Offline Vidya

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Re: Explain reaction of propene with Cl2 and H2O please
« Reply #6 on: September 29, 2016, 12:07:36 AM »
Halonium ion in general

Offline Babcock_Hall

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Re: Explain reaction of propene with Cl2 and H2O please
« Reply #7 on: September 29, 2016, 10:40:01 AM »
OK, so which carbon atom has the greater share of positive charge in this intermediate?

Offline Vidya

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Re: Explain reaction of propene with Cl2 and H2O please
« Reply #8 on: September 29, 2016, 10:47:39 AM »
the one which can form the stable carbocation or bonded to more electron donating groups....

Offline carotis

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Re: Explain reaction of propene with Cl2 and H2O please
« Reply #9 on: September 29, 2016, 07:28:13 PM »
I think that was a question to me sir :P
In general I assume the more substituted one (less H atoms) draws the OH nucleophile.

Offline carotis

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Re: Explain reaction of propene with Cl2 and H2O please
« Reply #10 on: September 29, 2016, 07:52:37 PM »
I am curious now what concerns the hdrid shift.. lets say, we have 4-cyclohexyl-1-butene and do same raction with Cl2 and H2O.
Textbook says we will receive 1-chloro-2-hydroxy-4-cyclohexylbutane.
However, if we look at it, we also have a tertiary carbon, the one at the cyclohexane group, so... is a hydrid shift possible or is it too far away to matter anything in this direction? I wiould assume we would get more the hydroxy group at the tertiary carbon, if we follow theoretical logic. Same lets say with an Dodecane-alkene, would the distance be "too big" to perfectly induce a hydrid shift or perhaps is the reason a very different. Perhaps the Halonium ion stabilizes the intermediate (similiary yet not quite like in oxymerucaration process) and the followed mechanism is merely a "break" with a backstab attack ;D
« Last Edit: September 29, 2016, 08:15:37 PM by carotis »

Offline orgopete

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Re: Explain reaction of propene with Cl2 and H2O please
« Reply #11 on: September 30, 2016, 06:28:31 PM »
This is one of those good questions. This is how I view it. The answer depends on what the driving force or what makes the reaction take place. This could be part of a general reaction of three-membered rings. A cyclopropane is rather more resistant to opening. An aziridine can open especially if aided by a leaving group. An epoxide can open under nucleophilic conditions or electrophilic conditions. If nucleophilic, then the nucleophile attacks as the least substituted carbon. If electrophilic, a weak electrophile is unable to open an epoxide directly. If the epoxide is treated with an acid, opening will now occur under a more SN1-like center. The nucleophile will attack the more stable carbocation "intermediate".

A chloronium or bromonium ion is similar to the protonated epoxide in being a good leaving group. Water could attack at either carbon. The identity of the product should indicate whether the reaction is SN2-like or SN1-like. Are the electrons of water sufficiently nucleophilic to initiate an attack on the less substituted carbon? Do the electrons need more positive charge to effect its attack? It is the latter case, but it still does not seem to react as an SN1 mechanism. The reaction with cyclohexene gives the trans chloro or bromoalcohol. So, the net reaction is SN2-like with SN1 regiochemistry.

Interestingly, I searched for a reaction of 1-methylcyclohexene oxide. Methoxide opens it with opening at the less hindered side and trans-diaxial opening. Under acidic conditions, I saw a Professor Wamser reporting methanol opening the epoxide to give the 2-methoxy-2-methyl-1-cyclohexanol of trans opening and with ethanol give a mixture of cis and trans I don't know the actual product, but I could imagine either.

Re: rearrangements
This can often be difficult to predict very well. I think that if there is a neighboring pair of non-bonded electrons, they will always react with a carbocation faster than any rearrangement. That would be consistent with a lack of rearrangement of bromination or oxymercuration reactions. The non-bonded electron of bromine or mercury react faster than bonded electrons of a hydride, for example. That is why oxymercuration reactions do not give rearrangements while simple acid catalyzed hydrations may.
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