Publication

Enhancement of benzylic basicity by a fluorine substituent at the para-position: a case of lone pair/lone pair repulsion

Manfred Schlosser
2000
Journal Articles

Abstract

The introduction of a halogen atom at any arom. position of toluene considerably accelerates the base-promoted deprotonation of the Me group. P-Fluorotoluene is the only exception; proton abstraction from its benzylic site occurs approx. at one tenth of the rate found with toluene (at -75 Deg). Lone-pair repulsion appears to be at the origin of the decrease in acidity. Chloro- and bromotoluenes instantaneously exchange benzylic hydrogen against metal when treated with soln. of lithium 2,2,6,6-tetramethylpiperidide (LITMP) in di-Et ether in the presence of potassium tert-butoxide and N,N,N',N",N"-pentamethyldiethylenetriamine at -100 Deg. Due to extensive side reactions ("aryne" formation as a consequence of concomitant deprotonation of arom. sites adjacent to the halogen atom), products can be isolated only in moderate yield (10-35%), but they are regioisomerically pure. [on SciFinder (R)]

Official source

https://infoscience.epfl.ch/entities/publication/48dc19ad-92f8-4479-bb21-58eefa5950b7

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Manfred Schlosser
2000
Journal Articles

Abstract

Official source

https://infoscience.epfl.ch/entities/publication/48dc19ad-92f8-4479-bb21-58eefa5950b7

About this result

Related concepts (22)

Lone pair

In chemistry, a lone pair refers to a pair of valence electrons that are not shared with another atom in a covalent bond and is sometimes called an unshared pair or non-bonding pair. Lone pairs are found in the outermost electron shell of atoms. They can be identified by using a Lewis structure. Electron pairs are therefore considered lone pairs if two electrons are paired but are not used in chemical bonding. Thus, the number of electrons in lone pairs plus the number of electrons in bonds equals the number of valence electrons around an atom.

Halogen

The halogens (ˈhælədʒən,ˈheɪ-,-loʊ-,_-ˌdʒɛn) are a group in the periodic table consisting of six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts), though some authors would exclude tennessine as its chemistry is unknown and is theoretically expected to be more like that of gallium. In the modern IUPAC nomenclature, this group is known as group (XVII) or group (VII). The word "halogen" means "salt former" or "salt maker".

Carbon–fluorine bond

The carbon–fluorine bond is a polar covalent bond between carbon and fluorine that is a component of all organofluorine compounds. It is one of the strongest single bonds in chemistry (after the B–F single bond, Si–F single bond, and H–F single bond), and relatively short, due to its partial ionic character. The bond also strengthens and shortens as more fluorines are added to the same carbon on a chemical compound. As such, fluoroalkanes like tetrafluoromethane (carbon tetrafluoride) are some of the most unreactive organic compounds.