[Imo]

What of theses have resonance structures ? electrons delocalized...
Is the 1,2,3,5 and 6?
http://imageshack.us/photo/my-images/705/semttulocak.png/

[Schrödinger]

Yes, the others are isolated systems. No resonance is possible in them

[Imo]

Why 3 has resonance?

[Imo]

I think this : http://imageshack.us/photo/my-images/171/27743918.png/

But will have one charge negative, not positive. Can anyone make the resonance for me? or explain...

[Schrödinger]

No. Once that pi bond moves to O⁺, it becomes neutral and the adjacent carbon becomes positively charged, because it has just lost a pi bond's electron. So, basically, the positive charge migrates from O to C and if you keep this up with the ext pi bond, you can see that the potive charge is delocalized over the entire ring.

[Imo]

Is this http://imageshack.us/photo/my-images/854/68570334.png/   ?
I only can get 1 structure of resonance. A pi bond breaks down and only it...

[Schrödinger]

Correct. Now use the other pi bond that is in conjugation with the positive charge (the C=C double bond has a pi bond you can use)

[Imo]

How is the solution for 2 ?
http://imageshack.us/photo/my-images/268/81839705.png/

I did it, but anything is wrong...

 For 6 these are only 2 structures of resonance?
http://imageshack.us/photo/my-images/138/molk.png/
http://imageshack.us/photo/my-images/40/moll.png/

[Imo]

Forget the previous post ... what worries me is this:
To draw resonance structures of the compound, usually write:
http://imageshack.us/photo/my-images/713/15616772.png/
But can or should I do so?
http://imageshack.us/photo/my-images/339/85919308.png/
because it is more detailed...is wrong?

[orgopete]

what worries me is this:
To draw resonance structures of the compound, usually write:
http://imageshack.us/photo/my-images/713/15616772.png/
But can or should I do so?
http://imageshack.us/photo/my-images/339/85919308.png/
because it is more detailed...is wrong?

Wrong? Sort of. It is probably more wrong because of convention than by fact. What is wrong is to have ten electrons surrounding carbon. Clearly the transition state of an SN2 reaction has ten electrons and an alternate resonance form of a nitro nitrogen has ten electrons, so seeing ten electrons may not be so wrong. However, the convention is to maintain the octet rule in drawing resonance structures. So the first example correctly simultaneously breaks a bond to avoid ten electrons. You should follow that example. I would also advocate drawing the curved arrows as well. Although you did not make any errors in the resultant electron movements, the curved arrows are very useful in determining how they should move. It is not unusual for a student to correctly draw a curved arrow, but upon looking at a structure think the electrons should have a different arrangement and draw a resonance structure inconsistent with the curved arrows.

[Imo]

the convention is to maintain the octet rule ?
But here: http://imageshack.us/photo/my-images/824/digitalizar0040.jpg/

The second, with O+, yours structures of resonances dont complete the octet rule...the carbons will have 7 eletrons...yeah? 
is correct?

[orgopete]

Okay, my error in not explaining fully. The octet rule applies to not exceeding eight electrons. Granted, carbon for example can have fewer than eight electrons and one can find many examples in which it does not have eight. I meant you cannot have ten (valence) electrons around B, C, N, O, or F.