What are the resonance structures for [H2CNO2]-? The problem asks for the major and minor contributors. The answer key says that there are two structures in which the only double bond switches between the two NO bonds. (Both have the same energy-in other words no minor contributors)
My question is why can't there be a structure in which there's a single bond between all of the atoms? Also why can't there be a structure in which there's a double bond between the C and N atoms? For both situations the overall charge would still be -1.
My other question is when drawing resonance structures the number of unpaired electrons should be the same but I've seen examples (like for [CH3OCH2]+) in which there's two pairs of unpaired electrons for the minor contributor but one pair for the major contributor. Why is this? Is this rule only for structures of the same energy?