Concept on carbocation

[HannibalLecter]

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OK I know that tertiary carbocations are more stable than primary or what not.

I am asking why is it? I know the alkyl groups are electron donating but if you look at the molecular level:

Hydrogen's electronegativity is lower than Carbons, right? So it would give up its electrons (2 in the bond) to carbon. Right? But when carbon is attached to that carbon they share the electrons between the bonds (2) so it would be actually less electron donating than hydrogen being attached.

Or

Is it because all the hydrogens on CH3 are actually donating their electrons to the carbon which in turn would exhibit a higher electron carrying potential and donate more to the carbon next to it?

Thoughts?

 

[LaughingGas]

OK I know that tertiary carbocations are more stable than primary or what not.

I am asking why is it? I know the alkyl groups are electron donating but if you look at the molecular level:

Hydrogen's electronegativity is lower than Carbons, right? So it would give up its electrons (2 in the bond) to carbon. Right? But when carbon is attached to that carbon they share the electrons between the bonds (2) so it would be actually less electron donating than hydrogen being attached.

Or

Is it because all the hydrogens on CH3 are actually donating their electrons to the carbon which in turn would exhibit a higher electron carrying potential and donate more to the carbon next to it?

Thoughts?

http://en.wikipedia.org/wiki/Hyperconjugation

 

[LetsGo2DSchool]

Actually hydrogen and carbon are almost equivalent in electronegativity. I can't remember the electronegativity values off the top of my head, but they're very similar if not identical.

 

[UCF FINatic]

Actually hydrogen and carbon are almost equivalent in electronegativity. I can't remember the electronegativity values off the top of my head, but they're very similar if not identical.

This is correct. C-H and basically non-polar covalent bonds since they are pretty much equal in terms of electron negativity.

The reason tertiary is better than secondary which is better than primary is the fact that the positive charge could be spread out among more carbons. Hope that helps.

 

[HannibalLecter]

Actually google states carbon's electronegativity is at 2.55 and hydrogen's electronegativity is at 2.20. So hydrogen is actually less electronegative than carbon. So in a bond the electrons would actually be more towards the carbon in this case.

I think the more appropriate answer for my question was: hyperconjugation

And, I looked it up and it definitely solved my question thank you guys for the input:

http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch04/ch4-3-2-1.html

 

[LetsGo2DSchool]

Actually google states carbon's electronegativity is at 2.55 and hydrogen's electronegativity is at 2.20. So hydrogen is actually less electronegative than carbon. So in a bond the electrons would actually be more towards the carbon in this case.

Nonpolar covalent bond is defined as an electronegativity difference of 0.4 - 1.7

Ionic bond is defined as an electronegativity difference of greater than 1.7

The difference between the electronegativities of carbon and hydrogen is less than 0.4 and thus, it's basically identical meaning there is equal sharing of electrons between the two atoms.

I remember this from my Orgo textbook.

 

[HannibalLecter]

Yes thats the simplified version but what if on the DAT you were given to figure out the actual oxidation state C2 of say CH3CH2CH3? What would your answer be then?

You have to be able to break down further to the most molecular level detail to explain a problem. Yes I know that electronegativity difference of very little will reveal a nonpolar covalent bond. .4-1.7 yields a polar covalent bond. But even in a nonpolar covalent bond those electrons are feeling a little electrical charge on them from the more electronegative carbon. Its just way way way more apparent in a polar covalent bond.

 

[Potatochips]

yeap you are right hyperconjugations are considered as a pretty important factor in college level ochem

 

[wired202808]

Yes thats the simplified version but what if on the DAT you were given to figure out the actual oxidation state C2 of say CH3CH2CH3? What would your answer be then?

You have to be able to break down further to the most molecular level detail to explain a problem. Yes I know that electronegativity difference of very little will reveal a nonpolar covalent bond. .4-1.7 yields a polar covalent bond. But even in a nonpolar covalent bond those electrons are feeling a little electrical charge on them from the more electronegative carbon. Its just way way way more apparent in a polar covalent bond.

I believe orbitals are not tested on the DAT in terms of homo and lumo, only in regards to hybridization, and knowing/counting sigma and pi bonds.