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Topic: Why are Silyl cations unstable  (Read 1905 times)

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Offline ryin0

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Why are Silyl cations unstable
« on: August 25, 2021, 12:24:37 PM »


Comparing the electronegativity of Si to C, you would expect Si to be better at distributing positive charge
Was wondering why Silyl cations are so particularly unstable that their formation isn't comparable to carbocation formation

Offline Corribus

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Re: Why are Silyl cations unstable
« Reply #1 on: August 25, 2021, 01:20:18 PM »
Silicon is a lot bigger than carbon. Could it be that it's harder to sterically protect the reactive silicon center?
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

Offline Babcock_Hall

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Re: Why are Silyl cations unstable
« Reply #2 on: August 25, 2021, 04:47:52 PM »
Carbocations are said to be stabilized by hyper-conjugation.  My hand wave is that this mechanism may be more difficult in the case of silicon owing to problems in achieving good overlap.  I would be hesitant to invoke electronegativity in any case.  IIUC electronegativity was originally an explanation for the various strengths of covalent and polar covalent bonds.

Offline Corribus

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Re: Why are Silyl cations unstable
« Reply #3 on: August 25, 2021, 05:36:26 PM »
Carbocations are said to be stabilized by hyper-conjugation.  My hand wave is that this mechanism may be more difficult in the case of silicon owing to problems in achieving good overlap.
Not a bad hand-wave. Silicon is poor at making pi bonds for the same reason.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

Offline wildfyr

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Re: Why are Silyl cations unstable
« Reply #4 on: August 25, 2021, 11:06:17 PM »
I agree, Babcock that is at least a strongly contributing factor to the lower stability.

Offline ryin0

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Re: Why are Silyl cations unstable
« Reply #5 on: August 26, 2021, 11:50:52 AM »
thanks ya'll!

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