Resonance and aromaticity

Move electrons within conjugated systems present in molecules to find as many resonance contributors as possible.

The goal of this chemlet is to help you

  • learn to quickly identify conjugated sytems in structural diagrams.
  • learn which resonance structures contribute most to the stability of molecules.
  • understand that the actual structure is a hybrid of all its resonance contributors.

Stereocenter descriptors (R and S)

Follow the most commonly used CIP (Cahn-Ingold-Prelog) rules to determine the absolute configuration of stereocenters present in a molecule.

The goal of this chemlet is to help you

  • identify which atoms in a molecule are stereocenters.
  • practice the use of CIP rules to determine which of the possibly many stereoisomers is being shown to you.
  • understand how 3D information about a molecule is presented in structural diagrams.

Protonation and deprotonation

Protonate or deprotonate atoms in a molecule to indicate the dominant species in an aqueous solution at a given pH.

The goal of this chemlet is to help you

  • identify which atoms in a molecule constitute functional groups that are Brønsted-Lowry acids or bases.
  • discover that amphiprotic molecules exist.
  • use external resources to find the dissociation constants (pKa values) of a molecule.
  • familiarize yourself with the pKa values associated with functional groups and how they are influenced by the functional group's position within a molecule.
  • determine the effect of an aqueous solution's pH on the structure of dissolved molecules; leading to the formation of ions or zwitterions, for example.
  • understand how the pH of a solution ultimately affects molecular properties such as charge, polarity, solubility, hydrophilicity and reactivity.

Functional groups

Identify important functional groups that are present in biologically relevant molecules.

The goal of this chemlet is to help you

  • familiarize yourself with metabolites, pharmaceuticals, and the functional groups that give rise to their unique properties.