Electrophilic hydrogen-deuterium

Electrophilic Attack. A variety of boranes, heteroboranes, and metaHaboranes undergo electrophilic substitution. SusceptibiUty of boranes to electrophilic attack is often detected by deuteron—proton exchange experiments. Eor example, electrophilic hydrogen—deuterium exchange of occurs at the l-,2-,3-, and 4-positions when exposed to DCl in the presence of AlCl (81). The trend to increasing positive sites in is... 

From the present data it is impossible to determine whether tt- (I) or CT-complex (II) formation, or some other process, is rate determining, or to define the stereochemistry when going from (II) to (III). It is certain, however, that a strongly chemisorbed aromatic is involved at some stage. It is improbable that the defect sites produced by dehy-droxylation (69,70) are directly involved in the electrophilic hydrogen-deuterium exchange process. 

Azaindolizine, 5-chloro-nucleophilic substitution, 4, 458 8-Azaindolizine, 7-chloro-nucleophilic substitution, 4, 458 Azaindolizines basicity, 4, 454 electronic spectra, 4, 445 electrophilic substitution, 4, 453 halogenation, 4, 457 hydrogen/deuterium exchange, 4, 458 NMR, 4, 447, 449 nucleophilic attack, 4, 458 protonation, 4, 453 reaction with isothiocyanates, 4, 513 reactions, 5, 267 reviews, 4, 444 UV spectra, 4, 446, 449 Azaindolizines, amino-tautomerism, 4, 452... 

Beyer synthesis, 2, 474 electrolytic oxidation, 2, 325 7r-electron density calculations, 2, 316 1-electron reduction, 2, 282, 283 electrophilic halogenation, 2, 49 electrophilic substitution, 2, 49 Emmert reaction, 2, 276 food preservative, 1,411 free radical acylation, 2, 298 free radical alkylation, 2, 45, 295 free radical amidation, 2, 299 free radical arylation, 2, 295 Friedel-Crafts reactions, 2, 208 Friedlander synthesis, 2, 70, 443 fluorination, 2, 199 halogenation, 2, 40 hydrogenation, 2, 45, 284-285, 327 hydrogen-deuterium exchange, 2, 196, 286 hydroxylation, 2, 325 iodination, 2, 202, 320 ionization constants, 2, 172 IR spectra, 2, 18 lithiation, 2, 267... 

The intermediate tricyclic ketones 495 and 496 have been transformed to the methoxy-substituted derivative 97284,285) latter ketone is subject to hydrogen-deuterium exchange only under basic conditions and appears to exist entirely in the keto form despite the ready formation of its anion and successful methylation on oxygen . In agreement with the aromatic nature of 490, the hydrocarbon undergoes electrophilic substitution reactions... 

The very high reactivity of pyrrole compared with furan in electrophilic substitutions is also confirmed by rate measurements of hydrogen-deuterium exchange in methanol-water-sulfuric acid mixtures53 (Table VI). The rate of exchange of pyrrole-2-d in 0.5%... 

You have now seen how enols and enolates react with electrophiles based on hydrogen (deuterium), carbon, halogens, silicon, sulfur, and nitrogen. What remains to be seen is how new carbon-carbon bonds can be formed with alkyl halides and carbonyl compounds in their normal electrophilic mode. These reactions are the subject of Chapters 26-29. We must first look at the ways aromatic compounds react with electrophiles. You will see similarities with the behaviour of enols. 

Electrophilic hydrogen exchange in deuterioselenophenes was studied using a 4 1 mixture of acetic and trifluoroacetic acids.79 Rate constants and partial rate factors were determined for the deuterium replacement at 25°C (see Table IV). Rate constants were calculated... 

Curulli, A. and Slcitcr, G., Electrophilic heteroaromatic substitutions. VIII. Studies on the mechanism of the a-side-chain aminomethy-lation and hydrogen/deuterium isotope exchange reactions of a-methylpyrroles, J. Org. Chem... 50, 4925, 1985. 

---