Aromatic compounds hydrogen isotope exchange reactions

Hydrogen isotope efiects in aromatic substitution reactions, 2, 163 Hydrogen isotope exchange reactions of organic compounds in liquid ammonia, 1, 156... 

Alkylcarbonium ions, spectroscopic observation in strong acid solutions, 4, 305 Ammonia, liquid, isotope exchange reactions of organic compounds in, 1, 156 Aromatic substitution, a quantitative treatment of directive effects in, 1, 35 Aromatic substitution reactions, hydrogen isotope effects in, 2, 163 Aromatic systems, planar and non-planar, 1, 203... 

Benzannelation results in an attenuation of aromaticity effects in 4n + 2rc-systems.255 The base-catalyzed hydrogen isotope exchange and isomerization reactions of isomeric dihydrobenzazocines 135 and 136 show these compounds have moderately enhanced kinetic acidity as compared with dihydroquinoline models and is attributable to a small degree of aromatic stabilization in the incipient 1()n electron benzazocinyl anions.255... 

Because aromatic compounds are subject to electrophilic attack, D+ provides a ready entry of deuterium into the aromatic molecule. The reaction of various anhydrides with D2O is one of the most common methods for providing protic acids. The acidity of protic acids can be enhanced by co-catalysts , which are usually Lewis acids. Hence electrophilic substitutions by protic acids and Lewis acids are of primary interest in hydrogen isotope exchange. 

The present article is a review of tt complex adsorption which has recently been proposed in catalytic reaction mechanisms (2-11). The main evidence for this intermediate has been obtained from isotopic hydrogen exchange reactions with aromatic compounds where an interpretation according to classical theories has met with increasing difficulties. The limitations of the classical associative and dissociative exchange mechanisms originally proposed by Horiuti and Polanyi (12) and Farkas and Farkas (13-15) re discussed. This is followed by a... 

It is possible to replace the ring hydrogens of many aromatic compounds by exchange with strong acids. When an isotopically labeled acid such as D2S04 is used, this reaction is an easy way to introduce deuterium. The mechanism is analogous to other electrophilic substitutions ... 

A good example of behaviour of this kind is provided by the ionization of carbonyl compounds (equation 6), to which additional data for proton transfer from nitroalkanes to various bases may be added [13, 14]. The isotope effect on these reactions rises to a maximum of 10 at AG° = 0, just where the Bronsted exponent is one-half, and it falls off to considerably lower values on either side of this point. The endothermic side of AG° = 0 is particularly well documented here kyjk-o drops to about 3 when AG° 25 kcal mole" and the Bronsted exponent becomes ca. 0.9. Aromatic hydrogen exchange shows a similar correspondence between isotope effect [15] and Bronsted exponent [16], and additional examples may be found in the hydrolysis of vinyl ethers [17] and diazocompounds [18], as well as in the diazo-coupling reaction [19]. 

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