CHE 230
University of Kentucky
Draw the substitution product
Erase the bond between the electrophilic C atom and the leaving group, and create a new bond between the electrophilic C atom and the nucleophilic atom.
- If the nucleophilic atom is negatively charged, it is neutral in the product.
- If the nucleophilic atom bears a metal, the bond between the nucleophilic atom and the metal is also cleaved in the product, and the nucleophilic atom remains uncharged.
- If the nucleophilic atom bears an acidic H atom, usually the bond between the nucleophilic atom and the H atom is also cleaved in the product, and the nucleophilic atom remains uncharged. (Exception: If the nucleophilic atom is N, the N–H bond may be retained in the product. If it is retained, then the N becomes positively charged.)
- If the nucleophilic atom is a neutral, lone-pair-bearing atom that does not have an acidic H atom, it is positively charged in the product.
- The electrophilic C atom's formal charge remains unchanged.
- It is customary not to draw the product that contains the leaving group. If you do choose to draw it, the atom of the leaving group that was attached to the electrophilic C decreases its formal charge by one. However. if the conditions are acidic, and the leaving group is uncharged before it leaves, it may pick up an H atom before it leaves; if so, it is uncharged after it leaves.
Furthermore, if the electrophilic C atom is stereogenic and configurationally pure:
- If the reaction conditions are basic (SN2 mechanism), then the electrophilic C atom's configuration becomes inverted in the product (bold to hashed or vice versa). If the nucleophile and the leaving group are assigned the same priority with respect to the other substituents on the electrophilic C atom, the configuration will change from R to S or vice versa.
- If the reaction conditions are acidic (SN1 mechanism), then the electrophilic C atom's configuration becomes scrambled in the product (wavy bond).