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nother chem question - formal charge


Sarahisme

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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.

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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.

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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

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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

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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))

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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.

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