A leaving group is an atom or group of atoms that detaches from a chemical substance. The remaining molecule or fragment remaining is known as the residual or main part. The term leaving group is dependent on the context of the statement.^[1] Properties For other meanings of Atom, see Atom (disambiguation). ...

The ability for a functional group to leave is called lability. Leaving groups affect the intrinsic reactivity, not the nucleophilic discrimination factors. In organic chemistry, functional groups (or moieties) are specific groups of atoms within molecules, that are responsible for the characteristic chemical reactions of those molecules. ... Lability is constantly undergoing change or something that is likely to undergo change. ...

The lower the pK_a of the conjugate acid, the better the leaving group. This is because the lower the pKa of the conjugate acid of the leaving group, the more it stays in its anion (leaving groups may be neutral), leaving group, form. This anion stability means that the leaving group is less likely to react with the cation formed by the leaving group's absence (this is the case with bad leaving groups). Without stabilization, a leaving group will become a nucleophile due to its negative charge, and if this happens, the reaction goes in circles. This is why a strong base is a poor leaving group. S_N1 reactions prefer halides, pseudohalides, and non-coordinating ions as leaving groups. Halide salts are particularly useful leaving groups because they can be abstracted by silver ions, to form insoluble silver halides. The acid dissociation constant (Ka), also known as the acidity constant or the acid-ionization constant, is a specific equilibrium constant for the reaction of an acid with its conjugate base in aqueous solution [1]. // When an acid dissolves in water, it partly dissociates forming hydronium ions and its conjugate... Within the Brønsted-Lowry (protonic) theory of acids and bases, a conjugate acid is the acid member, HX, of a pair of two compounds that transform into each other by gain or loss of a proton. ... Acids and bases: Acid-base extraction Acid-base reaction Acid dissociation constant Acidity function Buffer solutions pH Proton affinity Self-ionization of water Acids: Lewis acids Mineral acids Organic acids Strong acids Superacids Weak acids Bases: Lewis bases Organic bases Strong bases Superbases Non-nucleophilic bases Weak bases edit In... The SN1 reaction is an substitution reaction in organic chemistry. ... A halide is a binary compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative than the halogen, to make a fluoride, chloride, bromide, iodide, or astatide compound. ... A halide is a binary compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative than the halogen, to make a fluoride, chloride, bromide, iodide, or astatide compound. ... Anions that interact weakly with cations are optimistically termed non-coordinating anions, although a more accurate term is weakly coordinating anion.[1] Non-coordinating anions are useful in studying the reactivity of electrophilic cations. ... A silver halide is one of the compounds formed between silver and one of the halogens, usually silver bromide (AgBr), silver chloride (AgCl) and silver iodide (AgI). ...

In room temperature water, the sequence of lability is: For other uses, see Room temperature (disambiguation). ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ...

• Less lability
• amine NH₂⁻
• methoxy CH₃O⁻
• hydroxyl HO⁻
• carboxylate CH₃COO⁻
• F⁻
• water
• Cl⁻
• Br⁻
• I⁻
• azide N₃⁻
• thiocyanate SCN⁻
• nitro NO₂
• Greater Lability

  NO₃⁻ is also weaker than F⁻.

A direct application of the difference in leaving group stability is in the carboxylic acid derivatives. The worse the leaving group, the more stable the chemical, which makes these form a hierarchy that can be separated in the lab. Amines, which are the worst leaving group, are the most stable compound, and attacking any carboxylic acid derivative with an amine produces an amide. Esters are the second most stable followed by anhydrides and finally halides. The general structure of an amine Amines are organic compounds and a type of functional group that contain nitrogen as the key atom. ... In chemistry, the methoxy prefix indicates the function group consisting of the methyl group and oxygen. ... // Hydroxyl group The term hydroxyl group is used to describe the functional group -OH when it is a substituent in an organic compound. ... Structure of a carboxylic acid Carboxylic acids, also known as alkanoic acids, are organic acids characterized by the presence of a carboxyl group and have the general chemical formula R-C(=O)-OH, also written as R-COOH, where R is a hydrogen or an alkyl group. ... Fluoride is the ionic form of fluorine. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... The chloride ion is formed when the element chlorine picks up one electron to form an anion (negatively-charged ion) Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. ... A bromide is a phrase, or person who uses phrases, which have been used and repeated so many times as to become either insincere in their meaning, or seem like an attempt at trying to explain the obvious. ... An iodide ion is an iodine atom with a −1 (negative one) charge. ... An azide is the N3- anion, the anion of hydrazoic acid or a reactive group in organic chemistry where a carbon substituent is attached as RN3. ... The structure and bonding of the thiocyanate ion Thiocyanate (also known as sulphocyanate or thiocyanide) is the anion, [SCN]−. Common compounds include the colourless salts potassium thiocyanate and sodium thiocyanate. ... Nitro may refer to: Nitroglycerin, an extremely explosive chemical compound Nitrous, a type of fuel additive for race cars Nitromethane, another type of fuel additive for race cars [[GlyceryBold textl trinitrate (pharmacology)]], a medical compound used for the treatment of angina pectoris Nitrogen, especially when used in draught beer Nitrocellulose... Structure of anhydride. ...

During the S_N2 nucleophilic attack, a partial negative charge forms on the leaving group. During S_N1 reactions, the leaving group anionizes and leaves. In general, amine, methoxy and hydroxyl groups never act as leaving groups in a substitution reaction. In chemistry, nucleophilic subsitution is a type of chemical reaction in which one nucleophile (electron donor) replaces another as a covalent substituent of some atom. ... In chemistry, a nucleophile (literally nucleus lover) is a reagent which is attracted to centres of positive charge. ... This article is about the electrically charged particle. ...

In the non-mechanistic transformations, leaving group is the actual substituent group present in the substrate and product. For other uses, see Substrate. ...

The structure of the leaving group affects the rates of both Sn1 and Sn2 reactions. In general, the more stable the leaving group is as a free species--that is after it has left--the faster it will leave. This stability also reflects the basicity of the species: the more stable it is, the weaker base it is.

See also

• Nucleofuge
• Electrofuge

A nucleofuge is a leaving group which retains the lone pair from its previous bond with another species. ... A electrofuge is a leaving group which does not retain the lone pair from its previous bond with another species. ...

References

1. ^ International Union of Pure and Applied Chemistry. "leaving group". Compendium of Chemical Terminology Internet edition.

IUPAC logo The International Union of Pure and Applied Chemistry (IUPAC) (Pronounced as eye-you-pack) is an international non-governmental organization established in 1919 devoted to the advancement of chemistry. ... Compendium of Chemical Terminology (ISBN 0-86542-684-8) is a book published by IUPAC containing internationally accepted definitions for terms in chemistry. ...

External links

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