Arrow Review
Arrow Review
We have seen several types of arrows so far. Let’s review the different types of arrows found in organic chemistry. Most of these are review, but here is one new one. A retrosynthetic arrow is the opposite of a regular reaction arrow. We use it when we are thinking about how we want to synthesize a particular product. When we ask, “What reactants would we mix together to make this product?” we are doing a retrosynthetic analysis. We use a retrosynthetic arrow to show we are thinking how to synthesize something.
Various arrows
Reaction Conditions
Symbols are sometimes written above the reaction arrows to indicate the reaction conditions. A small triangle is written above the arrow if the reaction is heated. It looks like the tip of a flame. One way to heat up an organic reaction to the boiling point of the solvent without losing the solvent is to perform a reflux. The solvent is boiled. The vapors travel up a condenser where they cool down, condense back into a liquid, and fall back into the reaction flask. An arrow pointing up and one pointing down is drawn over the reaction arrow if a reaction is heated to reflux. It represents the path the solvent travels. The symbol h is drawn above the reaction arrow if a reaction is placed under ultraviolet light. This comes from the equation for the energy of light E=h.
Reflux apparatus
Symbols for various reaction conditions
Sometimes, instead of writing all of the reactants in a reaction to the left side of the reaction arrow, they are written above or below the arrow to signify they are added to the reaction. If numbers are placed before the reactants, then they are added in that particular order. If numbers are not written before the reactants, then all reactants are added to the reaction at the same time.
How to write reactants on reaction arrows