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Topic: Chemical intuition and paradigms  (Read 6016 times)

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Offline mir

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Chemical intuition and paradigms
« on: March 30, 2006, 03:42:22 AM »
Where go the border between the socalled "chemical intuition" and the chemical paradigms we all share?

The reality is really more complicated than the simple models in chemistry:
Take markovnikov addition in organic chemistry as an example.
Chlorine often prefer to add to a double bond, anti-markovnikov through a radical intermediate.

Often the simple model of SN2 substitution is really a many-step process involving solventmolecules and charge-transfer complexes.

Is our intuition a uncertain road to follow, that easily brings us to the wrong solutions for complex systems?
And what does that say about the chemist? Have we learned anything else than to simple - not useful models (except in education)?
No single thing abides, but all things flow.
Fragment to fragment clings, and thus they grow
Until we know and name them.
Then by degrees they change and are no more
The things we know.
- Titus Lucretius Carus

http://www.ife.no

Offline AWK

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Re:Chemical intuition and paradigms
« Reply #1 on: March 30, 2006, 04:33:15 AM »
Quote
The reality is really more complicated than the simple models in chemistry:
It should be, otherwise chemistry (and other sciences) would be completely uninteresting.

Quote
Take markovnikov addition in organic chemistry as an example.
Chlorine often prefer to add to a double bond, anti-markovnikov through a radical intermediate.
Markovnikov rule comes from 1869 and represents the true mind of chemist at that time. Frankly saing, it is stiil too complex to many students.
Markovnikov rule is devoted for electrophilic, not for radical addition.

Quote
Often the simple model of SN2 substitution is really a many-step process involving solventmolecules and charge-transfer complexes.
Show example of involving charge-transfer complexes in SN2 substitution.
I think, you mix many mechanisms together, though from topological point of view the number of unique mechanisms in organic chemistry is a bit above 40.
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Offline mir

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Re:Chemical intuition and paradigms
« Reply #2 on: March 31, 2006, 04:33:18 AM »
Quote
Show example of involving charge-transfer complexes in SN2 substitution.
Maybe I mix something together. But I remember SNAr is something like a charge-transfer complex. The bondbreaking of the leaving group is very late in som cases.

Quote
though from topological point of view the number of unique mechanisms in organic chemistry is a bit above 40.
Is there any places on the www where I can read a bit more about the general reactions, seen as a whole? What is your source?

The reason why I want to have a discussion around the paradigms and "rules" of chemistry, is maybe a way for me to dare to walk outside the bubble and to think by myself. In the groundcourses in chemistry there was a wrong way of seeing things, and a right one. Today, I am learning there is many thousands of different ways of seeing a reaction. And whitch way is right, and which is wrong - is up to you to decide by looking at the system and the conditions.

Its quite fascinating. But you are on your own in this system, because there is so few systems that is investigated into details. And that is a bit scary.
No single thing abides, but all things flow.
Fragment to fragment clings, and thus they grow
Until we know and name them.
Then by degrees they change and are no more
The things we know.
- Titus Lucretius Carus

http://www.ife.no

Offline AWK

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Re:Chemical intuition and paradigms
« Reply #3 on: March 31, 2006, 06:00:32 AM »
I was interested in this problem about 20 years ago. I think,the good startiong point for backward searching may be:
G. Fic, G. Nowak  The CSB Approach to Prediction of Chemical Reactions. Chemometrics and Intelligent Laboratory Systems 75 (2), 137-148, 2005 (Elsevir Sciece Direct)
« Last Edit: April 04, 2006, 05:47:38 AM by AWK »
AWK

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