Deprotonation
Encyclopedia
Deprotonation is the removal of a proton
(H+) from a molecule
, forming the conjugate base.
The relative ability of a molecule to give up a proton is measured by its pKa
value. A low pKa value indicates that the compound is acidic and will easily give up its proton to a base
. The pKa of a compound is determined by many things, but the most significant is the stability of the conjugate base, which is determined mainly by the ability (or inability) of the conjugated base to stabilize the negative charge. The negative charge is stabilized when it is distributed on a large surface or a long chain. One of the mechanisms that distribute the negative charge on a longer chain or a ring is resonance. The solvent can also assist in the stabilization of the negative charge on a conjugated base.
Bases used to deprotonate depend on the pKa of the compound. Where the proton is not particularly acid
ic, and, as such, the molecule does not give up its proton easily; a base stronger than the commonly known hydroxide
s is required. Hydride
s are one of the many types of powerful deprotonating agents. Common hydrides used are sodium hydride
and potassium hydride
. The hydride forms hydrogen
gas
with the proton from the other molecule. However, the production of hydrogen also means that deprotonation using agents that release hydrogen is dangerous and should be done in an inert
atmosphere
(e.g., nitrogen
), as the hydrogen can ignite with the oxygen in the air.
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
(H+) from a molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
, forming the conjugate base.
The relative ability of a molecule to give up a proton is measured by its pKa
PKA
PKA, pKa, or other similar variations may stand for:* pKa, the symbol for the acid dissociation constant at logarithmic scale* Protein kinase A, a class of cAMP-dependent enzymes* Pi Kappa Alpha, the North-American social fraternity...
value. A low pKa value indicates that the compound is acidic and will easily give up its proton to a base
Base (chemistry)
For the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...
. The pKa of a compound is determined by many things, but the most significant is the stability of the conjugate base, which is determined mainly by the ability (or inability) of the conjugated base to stabilize the negative charge. The negative charge is stabilized when it is distributed on a large surface or a long chain. One of the mechanisms that distribute the negative charge on a longer chain or a ring is resonance. The solvent can also assist in the stabilization of the negative charge on a conjugated base.
Bases used to deprotonate depend on the pKa of the compound. Where the proton is not particularly acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
ic, and, as such, the molecule does not give up its proton easily; a base stronger than the commonly known hydroxide
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...
s is required. Hydride
Hydride
In chemistry, a hydride is the anion of hydrogen, H−, or, more commonly, a compound in which one or more hydrogen centres have nucleophilic, reducing, or basic properties. In compounds that are regarded as hydrides, hydrogen is bonded to a more electropositive element or group...
s are one of the many types of powerful deprotonating agents. Common hydrides used are sodium hydride
Sodium hydride
Sodium hydride is the chemical compound with the empirical formula NaH. It is primarily used as a strong base in organic synthesis. NaH is representative of the saline hydrides, meaning it is a salt-like hydride, composed of Na+ and H− ions, in contrast to the more molecular hydrides such as...
and potassium hydride
Potassium hydride
Potassium hydride, KH, is a chemical compound of potassium and hydrogen. It is a hydride of potassium. It reacts with water according to the reaction:...
. The hydride forms hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
with the proton from the other molecule. However, the production of hydrogen also means that deprotonation using agents that release hydrogen is dangerous and should be done in an inert
Inert
-Chemistry:In chemistry, the term inert is used to describe a substance that is not chemically reactive.The noble gases were previously known as inert gases because of their perceived lack of participation in any chemical reactions...
atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
(e.g., nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
), as the hydrogen can ignite with the oxygen in the air.