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Topic: Electrophilic additions to Alkenes and other pi bond additions  (Read 2321 times)

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Offline grignardattack

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I have an exam coming up and the unit covered includes over 20 new reactions. I understand most of them and how they work, but I would appreciate if the mechanisms/what the products will include could be clearly stated. The following reactions:
1. BH3 and H202
I understand this is anti markovnikov, no rearrangement. If the stereochemistry (syn) could be cleared up I would be grateful.

2. Br2/H20
I understand that the solvent does not participate and I was taught that the Br2 adds to both sides of the Carbon Carbon double bond. I would appreciate if the mechanism could be illustrated.

3.H2/Pt

Stereochem explained

4. Hg(OAc)2/NaBH4
Oxymercuration-demercuration. I understand that the NaBH4 "cuts" off the Hg(OAc)2, and that OAc is a good leaving group. I don't quite understand WHY that works, as well as knowing where to initially attach the Hg(OAc)2

5.CH3COOOH
 The simple way I was taught to draw the products is to add a 3-membered ring (with the O) between where the double bond is.

6. KMno4/H20 and OH-

I would appreciate the stereochemistry to be explained for this reaction.

I apologize if formatting is wrong. The biggest thing I struggle with is the mechanism behind the reaction and knowing how to have the correct stereochem in the reactions that require it.

Offline AWK

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Re: Electrophilic additions to Alkenes and other pi bond additions
« Reply #1 on: July 20, 2016, 01:40:33 PM »
Every advanced organic chemistry textbook explains these reactions. Also, searching internet (eg. GOOGLE) you can find many sites contained these reactions.
Eg. Google: addition borane to double bond
you can find:
http://chemwiki.ucdavis.edu/Textbook_Maps/Organic_Chemistry_Textbook_Maps/Map%3A_Organic_Chemistry_(Bruice)/04%3A_The_Reactions_of_Alkenes/4.11%3A_The_Addition_of_Borane_to_an_Alkene%3A_Hydroboration-Oxidation

http://www.masterorganicchemistry.com/reaction-guide/hydroboration-of-alkenes/
-shows stereochemistry for 1-methylcyclohexene and cis-3-methylpentene-2

as the first three sites
Go on for other problems.
AWK

Offline Babcock_Hall

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Re: Electrophilic additions to Alkenes and other pi bond additions
« Reply #2 on: July 20, 2016, 03:18:45 PM »
With respect to 4, what happens to the atom of mercury; in other words, what side-product is made?  Answering that question should help you understand the role of sodium borohydride.

Offline kriggy

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Re: Electrophilic additions to Alkenes and other pi bond additions
« Reply #3 on: July 20, 2016, 04:58:52 PM »
1) look for hydroboraition (-oxidation) reaction. It is tricky question, because the reaction follows markovnikov rule but the product in the end is anti-markovnikov (hint. what is electroplhile in BH3?)

2) mechanism goes via. 3 membered cyclic transition state that forces the Br- to come "from the other side" for more info google "bromination of alkenes"

3) see "catalytic hydrogenation"

5) not sure what you mean here? probably see epoxidation of alkenes

6) its very similar to upjohn dihydroxylation. Basicaly, both OH groups come from single molecule of KMnO4 and since the oxygens are boud to Mn they have to come from the same side

Offline spirochete

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Re: Electrophilic additions to Alkenes and other pi bond additions
« Reply #4 on: July 20, 2016, 05:59:51 PM »
1) look for hydroboraition (-oxidation) reaction. It is tricky question, because the reaction follows markovnikov rule but the product in the end is anti-markovnikov (hint. what is electroplhile in BH3?)


This depends what kind of markovnikov's rule your'e following. I just double checked and many sources (even reasonably good ones like organic-chemistry.org) will use the simple "H goes to the less substituted carbon" version of the rule.

I would like to at least give the original poster the more generalized version of Mark's Rule: "The electrophile goes to the less substituted carbon, the nucleophile goes to the more substituted carbon"

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