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The best Lewis structure for an oxocarbenium ion contains an oxygen–carbon double bond, with the oxygen atom attached to an additional group and consequently taking on a formal positive charge. In the language of canonical structures (or "resonance"), the polarization of the π bond is described by a secondary carbocationic resonance form ...
Oxocarbenium ions [ edit ] Another class of oxonium ions encountered in organic chemistry is the oxocarbenium ions, obtained by protonation or alkylation of a carbonyl group e.g. R−C= + O −R′ which forms a resonance structure with the fully-fledged carbocation R− + C −O−R′ and is therefore especially stable:
This group, under the reaction conditions, is activated and via the formation of an oxocarbenium is eliminated leaving an electrophilic anomeric carbon. A glycosyl acceptor is a sugar with an unprotected nucleophilic hydroxyl group which may attack the carbon of the oxocarbenium ion formed during the reaction and allow for the formation of the ...
Oxocarbenium and iminium ions have important secondary canonical forms (resonance structures) in which carbon bears a positive charge. As such, they are carbocations according to the IUPAC definition although some chemists do not regard them to be "true" carbocations, as their most important resonance contributors carry the formal positive ...
(Lewis acid) Any chemical species or molecular entity that acts as an electron pair acceptor when reacting with another species, forming a covalent bond by accepting a lone pair of electrons donated by the other species, which is known as a Lewis base. This definition was intended as a generalization of the Brønsted–Lowry definition by ...
Synthesis of nucleosides involves the coupling of a nucleophilic, heterocyclic base with an electrophilic sugar. The silyl-Hilbert-Johnson (or Vorbrüggen) reaction, which employs silylated heterocyclic bases and electrophilic sugar derivatives in the presence of a Lewis acid, is the most common method for forming nucleosides in this manner.
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Glucal, the glycal formed from glucose. Glycal is a name for cyclic enol ether derivatives of sugars having a double bond between carbon atoms 1 and 2 of the ring. The term "glycal" should not be used for an unsaturated sugar that has a double bond in any position other than between carbon atoms 1 and 2.