Organic Chemistry Key Concepts: Acids & Bases
-An acid is a proton donor: HA (acid) H (proton) + A (conjugate acid)
-A base is a proton receptor: B: (base) + H (proton) BH (conjugate acid)
-Acid and base reactions occur simultaneously. Every acid-base reaction must have both an acid (to
supply a proton) and a base (to accept the proton). Organic compounds act as weak acids and bases.
-For a general weak acid HA: HA + H O H O (aq) + A (aq) *The long arrow shows the
equilibrium position. *Neutrality = more stability than ionization.
K a [H O3][A] / [HA] pK a -log K a
-Recognize that as organic acids (weak) get stronger, their K gets laraer, and their pK gets smallea.
Concentrate on recognizing the structural features that affect acid (and base) strength.
-It is the pulling of an electron pair by an atom in a covalent bond that introduces reactivity. The stability
of A is a good indicator of acid strength. Any feature that weakens the HA bond and/or stabilizes the A
anion will shift the equilibrium to the right and increase acid strength.
-Electron motion is responsible for every molecular reaction.
-The more electronegative the atom bearing a hydrogen, the more acidic that hydrogen. Note that every
organic molecule that bears an H atom can act as an acid.
-Within a column of the periodic table, the larger the atom bearing a hydrogen, the more acidic that
hydrogen (the larger the atom, the more it can hold a negative charge). Note that size effect is more
important than electronegativity effects for elements in the same column.
-Electrons with more‘s’ character in their hybrid orbital are more electronegative. The sp hybrid orbital
makes hydrogen less prone to escape as the electrons are further away from A in the covalent bond.
-The stabilization (or destabilization) of charges by through-bond effects of neighbouring atoms is
termed an inductive effect.
-In general terms,