2.2 Curved Arrows: The Tools for Drawing Resonance Structures

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.