deprotonation

Examples of deprotonation in the following topics:

• Strong Bases

  • Strong bases either dissociate completely in solution to yield hydroxide ions, or deprotonate water to yield hydroxide ions.
  • Strong bases are capable of deprotonating weak acids; very strong bases can deprotonate very weakly acidic C–H groups in the absence of water.
  • They are called superbases, because it is not possible to keep them in aqueous solution; this is due to the fact they will react completely with water, deprotonating it to the fullest extent possible.

• Reactions of Alcohols

  • The mechanism includes three steps: 1) protonation; 2) nucleophilic addition of water to the resulting carbocation to form a protonated alcohol; 3) deprotonation of the protonated alcohol.
  • Alcohols can be deprotonated in the presence of bases to form alkoxide salts:
  • In basic conditions, which are required for E2, alcohols are deprotonated (see alkoxide formation) before they can be eliminated.
  • A weak base (typically a solvent) then deprotonates the most-substituted vicinal carbon, affording an e-isomer product.
  • From here, the water produced can deprotonate the carbocation to form a double bond:

• Elimination

  • A base then deprotonates a carbon adjacent to the carbocation, and the electrons from the previous C-H bond then go to form a C=C bond at the carbocation.
  • In bimolecular elimination (E2), a base deprotonates a carbon vicinal to a leaving group, and the electrons from the C-H bond form a double bond with the adjacent carbon, displacing the leaving group.
  • In the case of E2, at the time of deprotonation the hydrogen must be antiperiplanar to the leaving group.

• Salts that Produce Basic Solutions

  • Because it is capable of deprotonating water and yielding a basic solution, sodium bicarbonate is a basic salt.
  • But because HCl is a strong acid, the Cl- ion is not basic in solution, and it isn't capable of deprotonating water.

• Nature of Acids and Bases

  • A strong base is the converse of a strong acid; whereas an acid is considered strong if it can readily donate protons, a base is considered strong if it can readily deprotonate (i.e, remove an H+ ion) from other compounds.
  • As with acids, we often talk of basic aqueous solutions in water, and the species being deprotonated is often water itself.
  • Thus, deprotonated water yields hydroxide ions, which is no surprise.

• Aldehydes and Ketones

  • In the presence of a strong base, enolate formation and subsequent deprotonation of the enolate will occur.
  • However, the enol form is important for some reactions because the deprotonated enolate form is a strong nucleophile.

• Carboxylic Acids

  • Upon exposure to a base, the carboxylic acid is deprotonated and forms a carboxylate salt.

• Overview of the Acid-Base Properties of Salt

  • Sodium acetate is a basic salt; the acetate ion is capable of deprotonating water, thereby raising the solution's pH.

• Biomolecules

  • The peptide backbone also provides donor groups; these include deprotonated amides and the amide carbonyl oxygen centers (oxygen and nitrogen atoms as ligands).

• Boranes: Boron-Hydrogen Compounds