Drawing Resonance Structures—By Recognizing Patterns

PROBLEM 2.30 For the following compound, go through all three steps (making sure not to violate the two commandments) and draw the resonance structures. 

There are five patterns that you should learn to recognize to become proficient at drawing resonance structures. First we list them, and then we will go through each pattern in detail, with examples and exercises. Here they are  

A pi bond between two atoms, where one of those atoms is electronegative. 

Both examples exhibit a lone pair next to the pi bond. Next to means that the lone pair is separated from the double bond by exactly one single bond—no more and no less. You can see this in all of the examples below  

In each of these cases, you can bring down the lone pair to form a pi bond, and kick up the pi bond to form a lone pair  

Notice what happens with the formal charges. When the atom with the lone pair has a negative charge, then it transfers its negative charge to the atom that will get a lone pair in the end  

---