nother chem question - formal charge

[Sarahisme]

i don't agree with any of these answers: (but i am sure that i am wrong of course )....

 

so little help please if anyone has time

[Yggdrasil]

The answer is v. A carbon has four valence electrons, so when carbon has four electrons, it has a formal charge of 0. Carbon 1 has three bonds and no lone pairs giving it three electrons and thus a formal charge of +1 (less electrons, means more positive charge). Carbons 2 and 3 have four bonds, giving it 4 electrons and no formal charge. Oxygen atoms have six valence electrons, and oxygen 4 has one bond and three lone pairs giving it a total of 7 electrons (1 from the bond, and 6 from the lone pairs). Thus, the oxygen has a formal charge of -1.

[Sarahisme]

yeah thats what the answer booklet said, and i can see the correct results for 2,3 and 4 carbons

 

but for carbon 1, shouldnt there be 4 bonds to it?

[Yggdrasil]

There are only three bonds to the carbon in the diagram, not four. This may seem weird, since for carbon to have a full octet it needs four bonds, but it is possible to have a carbon atom without a full octet. Carbon 1 is what is known as a carbocation, an electron-defficient carbon. If you take organic chemistry, you'll see a lot of reactions involving carbocation intermediates.

[BenSon]

yeah thats what the answer booklet said, and i can see the correct results for 2,3 and 4 carbons

 

but for carbon 1, shouldnt there be 4 bonds to it?

Yggdrasil is right, also if it was attached to another bond then none of those answers would be right because then carbon one would have a 0 charge and the only answer with 0 for the first carbon is answer (i) and that is clearly wrong.

 

~Scott

[Sarahisme]

yeah ok, its just i thought if it did have only 3 bonds, then it would have at least one free electron...

??

[BenSon]

Nope, valance electrons (4) minus lone pairs (0) - Half the total number of electronsin reactions (3) equals formal charge of 1.

 

~Scott

[Sarahisme]

yeah its the lone pairs bit, i don't see how there can be no lone pairs (or lone electrons even, that are not in pair (i.e.. just one electron))

????

[BenSon]

Well there is no electrons paired or otherwise on the diagram around the carbon so i don't see where it would go. I understand where your coming from though it sems like it has four valence electrons and only three are being used so it should have a spare floating around. Aparently thats just not the way it sets itself up structually though, I don't know why it is like this but it is.

 

~Scott

[Yggdrasil]

yeah its the lone pairs bit' date=' i don't see how there can be no lone pairs (or lone electrons even, that are not in pair (i.e.. just one electron))

????[/quote']

 

Basically, a carbocation has an sp² hybridization and an empty p orbital. The empty p orbital makes carbocations very reactive, so they're highly unstable and you wouldn't be able to isolate one in a laboratory. However, they do exists, if briefly, as an intermediate.

 

Radicals (compounds having lone electrons not in pairs) similarly have an sp² or sp hybridization, carrying the lone electron in a p orbital.

[budullewraagh]

carbocations can be prepared in a laboratory, but in order to remain stable over a span of time, require the presence of superacids (HSbF6, H2FSO3, etc)

[Sarahisme]

allright, thanks for that