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2.2 Curved Arrows: The Tools for Drawing Resonance Structures
There are two important resonance structures in the compound above.
We separate resonance structures with a straight, two-headed arrow and place brackets around them.
The molecule is not moving between resonance structures.
We can begin to understand why resonance structures are so important now that we know why.
Ninety-five percent of the reactions you will see in this course occur because one molecule has a low electron density and the other molecule has a high electron density.
They attract each other in space.
To predict how and when two molecule will react with each other, we need to know where there is low electron density and high electron density.
To do this, we need a firm grasp of resonance.
Many examples of how to predict the regions of low or high electron density can be found in this chapter.
There are problems like this in the beginning of the course.
You will be expected to draw all of the resonance structures of a compound later on in the course.
You will be in big trouble later on if you can't do this.
You need to learn how to use curved arrows.
The arrows don't represent an actual process.
You will learn later about curved arrows used in drawing reaction mechanisms.
The arrows refer to the flow of electron density.
The curved arrows here are only used to help us draw the resonance structures of a molecule.
The electrons are not moving.
Since the electrons are stuck in one place, we need to move them from one drawing to another.
We use arrows to make sure we know how to draw resonance structures for a compound.
Let's look at the features of the arrows.
The head and tail of every arrow should be drawn in the correct place.
The tail and head need to be in the right place when drawing an arrow.
There are rules about where you can and can't draw arrows.
Since the arrows are describing the electrons, we need to talk about them.
A maximum of two electrons can be held by atomic orbitals.
electrons can be found in bonds or lone pairs electrons can only come from either a bond or a lone pair The electrons can only form a bond or a lone pair.
Let's start with the tails of arrows.
The tail of an arrow shows where the electrons are coming from.
The tail has to come from a place with electrons, either from a bond or a lone pair.
The electrons are coming from a bond.
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