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Q: Organic Chemistry ( Answered,   0 Comments )
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Subject: Organic Chemistry
Category: Science > Chemistry
Asked by: ronjon-ga
List Price: $10.00
Posted: 07 Apr 2004 07:05 PDT
Expires: 07 May 2004 07:05 PDT
Question ID: 326549
Why does Markovnikov's rule work?
Answer  
Subject: Re: Organic Chemistry
Answered By: livioflores-ga on 07 Apr 2004 08:06 PDT
 
Hi ronjon!!


According to Wikibooks ,the free textbook project, you can find an
article dedicated to the Markovnicov's rule:
http://wikibooks.org/wiki/Markovnikov's_rule_(Organic_chemistry)

Markovnicov's rule:
"Markovnikov's rule states that with the addition of HX, H2O, or ROH
to an alkene, the higher priority substituent adds to the more highly
substituted carbon of the carbon-carbon double bond, and the hydrogen
adds to the carbon that has more hydrogens."
http://wikibooks.org/wiki/Markovnikov's_rule_(Organic_chemistry)#Markovnikov's_rule

In this article you can read at the "Why it works" paragraph the following:
"Markovnikov's rule works because of the stability of carbocation
intermediates. Experiments tend to reveal that carbocations are planar
molecules, with a carbon that has three substituents at 120 to each
other and a vacant p orbital that is perpendicular to it in the 3rd
plane. The p orbital extends above and below the trisubstituent plane.
This leads to a stabilizing effect called hyperconjugation.
Hyperconjugation is what happens when there is an unfilled
(antibonding or vacant) C-C ? orbital and a filled C-H ? bond orbital
next to each other. The result is that the filled C-H ? orbital
interacts with the unfilled C-C ? orbital and stabilizes the molecule.
The more highly substituted the molecule, the more chances there are
for hyperconjugation and thus the more stable the molecule is.
Another stabilizing effect is an inductive effect."
http://wikibooks.org/wiki/Markovnikov's_rule_(Organic_chemistry)#Why_it_works



At the MSU (Michigan State University) Chemistry Department website I
found an article entitled "Addition Reactions of Alkenes", here you
will find the Markovnikov Rule statement and then they try to explain
what principles work in these addition reactions, finally they arrive
at a plausible rationalization of the Markovnikov's rule; due to
copyright rules and restrictions I can only give you the link:
http://www.cem.msu.edu/~reusch/VirtualText/addene1.htm


At the Western Illinois University website I found an article that
states, after a good and clear explanation, the following conclusion
"The stability order of carbocations provides a proof and support
Markovnikov's rule."
See the entire (1 page) document here:
"Electrophilic Addition to Alkenes"
http://www.wiu.edu/users/mftkv/Chem331/additiontoalkenes.html


For additional reference see:

"Markovnikov?s Rule explained":
http://www.chem.queensu.ca/people/faculty/mombourquette/FirstYrChem/organic/markovnikov.htm


"MARKOVNIKOV'S RULE":
http://www.uwplatt.edu/~sundin/354-7/l547-13.htm#mark


"Addition of Hydrogen Halides to Alkenes Markovnikov's Rule":
http://www-scf.usc.edu/~chem322a/ppt/Chapter_08/322a_Ch_8_02.pdf

"Markovnikov's Rule and Carbocation Stability":
http://www-scf.usc.edu/~chem322a/ppt/Chapter_08/322a_Ch_8_04.pdf


"Why Chemical Reactions Happen" by James Keeler and Peter Wothers 
Oxford University Press: New York, NY , 2003. 243 pp. ISBN 0199249733
From a review of this book by John Krenos I extract the following:
"Four reaction types to be examined and pertinent examples are
introduced in Chapter 1: precipitation and solubility reactions
(dramatic solubility differences between silver chloride and silver
nitrate in water); hydrolysis reactions (acyl chlorides react, amides
do not); carbenium ion formation (2-bromo-2-methylpropane forms one,
bromomethane does not); and reactions obeying Markovnikov?s rule (why
it works). The book?s goal is to understand the fundamental nature of
these reactions."
Read the review here:
http://jchemed.chem.wisc.edu/Journal/Issues/2004/Feb/abs201.html



Search strategy:
Markovnikov rule
Markovnikov's rule
Markovnikov's rule explained


I hope this helps you. Please feel free to request further assistance
if it needed via the clarification feature.

Best regards.
livioflores-ga
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