What do we call the set of compounds that are on the left of the reaction arrow

Reactants

I do believe they are the reactants.

Explanation:

In a reaction equation, there are:

Reactanst, Reactions, and Products

Usually in that order, the starting materials that are on the left are the reactants, they then react with eachother, creating a reaction that produces products, that come out on the left of an equation.