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![[Post New]](/templates/default/images/icon_minipost_new.gif) 12 Jan 2008 23:20:02 IST
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the mechanism involved in the addition of water to alkyne is given below... except the last step of tautomerisation,,,everything went over my head... PLEASE EXPLAIN EACH STEP.......... EACH STEP (you can ignore the tautomersiation step)
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salman khan |
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12 Jan 2008 23:44:51 IST
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Hg is in the form of Hg2+. Hence it can make bond wherever it finds place to make them.
Now triple bond C of alkyne is unsaturated, means these carbons can also make more bonds and also the charge density at this position is very high due to 3 bonds, hence Hg attacks this place and forms a temporary cyclic bond.
Now Hg was 2+ but the carbons were neutral, so after making bond, all the 3 species will be sharing that +2 charge will make both the carbons just partially positive which attracts the lone pair of O of water molecule.
The water molecule attacks a carbon atom, and the C-Hg bond breaks and Hg is left with one bond only.
Now + charge on an electronegative atom like O is unstable, hence H+ leaves to remove +ve charge from O.
Similarly another H2O, attacks the other C atom where Hg was hanging. This Hg bond is also broken and Hg which was working as catalyst is regained. Now as the medium is acidic, hence this time instead of OH, H+ comes to the C and it becomes CH2.
And then the tautomerisation.
Hope U understood.
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13 Jan 2008 12:36:46 IST
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tarinbansal's answer says........ "Now Hg was 2+ but the carbons were neutral, so after making bond, all the 3 species will be sharing that +2 charge will make both the carbons just partially positive which attracts the lone pair of O of water molecule.
The water molecule attacks a carbon atom, and the C-Hg bond breaks...." my problem If electron deficiency of the carbon atoms in the cycle is what attracts the oxygen of water, then the C attached to alkyl gr.(-R) is less electron deficient than the C attached to H due to +I effect of R. So Oxygen of water must add to the carbon attached to H (more electron deficient carbon)................ PLEASE CORRECT ME IF I AM WRONG........
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salman khan |
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13 Jan 2008 17:22:46 IST
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please reply
my problem is now concentrated ....
read the reply ater tarinbansal's reply
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salman khan |
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13 Jan 2008 18:25:30 IST
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OH biki,
I understud ur problem.
See this mechanism is a SN1>SN2 mechanism(read as MORE SN1 LESS SN2).
U need to know which reactions are SN1>SN2 and which R SN2>SN1.
Now here its SN1>SN2 it means that although a full-fledged carbocation is not formed but due to more priority to SN1, U need to see where the carbocation wud be stable if it wud hav been formed.
So here the carbocation wud hav been stable at C close to R, not at C which is attached to H.
Hence H2O attacks the C next to R.
Hope U got it.
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The quality of a person's life is in direct proportion to their commitment to excellence, regardless of their chosen field of endeavor.
It is during our darkest moments that we must focus to see the light.
Check out my blog at:
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Posts:
Can marks really judge a student??
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14 Jan 2008 10:44:43 IST
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@tarinbansal TWO MORE DOUBTS AND I SHALL CONSIDER YOU AS THE KING OF MECHANISM ...... 1)how to understand SN1<or> SN2 ?? and 2)what about the last H3O(+) attack.. ??
why doesn't it occur at the carbon attached to OH or rather why does it occur at the carbon attached to Hg(2+).
Answer it please...tarinbansal...
please friend ...
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salman khan |
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14 Jan 2008 11:03:06 IST
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that's in my XII !!!!
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it is not important where u stand, but in which direction u are moving |
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14 Jan 2008 14:37:01 IST
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ur mechanism needs some corrections.........
here is the correct mechanism.........now i hope u can
understand....
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"Nenenthedhavano naake teleedu"
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14 Jan 2008 18:22:52 IST
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@ tarin bansal .... 1)how to understand SN1<or> SN2 ?? and 2)what about the last H3O(+) attack.. ??
why doesn't it occur at the carbon attached to OH or rather why does it occur at the carbon attached to Hg(2+).
and @harsha read this and answer if possible ....... this mechanism is a SN1>SN2 mechanism(read as MORE SN1 LESS SN2).
U need to know which reactions are SN1>SN2 and which R SN2>SN1.
Now here its SN1>SN2 it means that although a full-fledged carbocation is not formed but due to more priority to SN1, U need to see where the carbocation wud be stable if it wud hav been formed.
So here the carbocation wud hav been stable at C close to R, not at C which is attached to H.
Hence H2O attacks the C next to R.
Now how to understand SN1<or> SN2 ?? and what about the last H3O(+) attack.. ?? why doesn't it occur at the carbon attached to OH or rather why does it occur at the carbon attached to Hg(2+).. ??
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salman khan |
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14 Jan 2008 22:57:39 IST
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Harsha,
there is hardly any diff in the mechanisms given by U and biki.
U added an extra step that H2O attacks the already attached H2O+ and H3O+ leaves, its the same thing if we say that H+ leaves. We only omit a step.
Biki,
I earlier mentioned that U cant predict whether SN1> OR SN2>. These are experimantal observations and U need to learn them wherever they r known.
Last H3O+ attacks as the lone pair of O is attracted towards highly positve Hg2+, so it removes Hg2+ and places a H+ instead.
Hope U got it.
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The quality of a person's life is in direct proportion to their commitment to excellence, regardless of their chosen field of endeavor.
It is during our darkest moments that we must focus to see the light.
Check out my blog at:
http://tarinbansal.blogspot.com/
Posts:
Can marks really judge a student??
Some myths about Chemical Engineering.
(A must see for every student)
Back to goiit, this time with Baby Veerappan. :D |
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15 Jan 2008 00:21:04 IST
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@tarinbansal thanx a lot frnd................. YOU ARE THE REAL KING .......... I LIKED YOUR APPROACH OF NOT CHANGING THE MECHANISM AND EXPLAINING IT IN YOUR OWN WAY....INSTEAD YOU STICKED TO MY ONE AND EXPLAINED IT WITH FULL PROFICIENCY........ THANX A LOT GOD BLESS..
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salman khan |
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15 Jan 2008 00:33:23 IST
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i shall make your altitude 1000 today and then sleep ...
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salman khan |
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15 Jan 2008 14:15:36 IST
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Arre biki,
plz yaar dont giv me so much honour.
I am not a king, the mechanism was taught to me that's why I knew it.
And thanx for making my altitude 1000 but there was no need of it at all.
Anyways, thanx.
And All the Best.
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The quality of a person's life is in direct proportion to their commitment to excellence, regardless of their chosen field of endeavor.
It is during our darkest moments that we must focus to see the light.
Check out my blog at:
http://tarinbansal.blogspot.com/
Posts:
Can marks really judge a student??
Some myths about Chemical Engineering.
(A must see for every student)
Back to goiit, this time with Baby Veerappan. :D |
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7 Feb 2008 22:25:24 IST
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Kucherov's Rxn
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______________________________________________
Siddhant Shah
The trouble with doing something right the first time is that nobody appreciates how difficult it is.
You can't control the wind, but you can adjust your sails.
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