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Heterocyclic organic chemistry is the branch of organic chemistry dealing with the synthesis, properties, and applications of organic heterocycles. [ 2 ] Examples of heterocyclic compounds include all of the nucleic acids , the majority of drugs, most biomass ( cellulose and related materials), and many natural and synthetic dyes.
The boat conformation (C, 6.9 kcal/mol, C 2v symmetry) is a local energy maximum for the interconversion of the two mirror image twist-boat conformers, the second of which is converted to the other chair confirmation through another half-chair. At the end of the process, all axial positions have become equatorial and vice versa.
It is a member of a larger class of isomerases which catalyze the interconversion of chemical isomers (in this case structural isomers of pentose). It plays a vital role in biochemical metabolism in both the pentose phosphate pathway and the Calvin cycle. The systematic name of this enzyme class is D-ribose-5-phosphate aldose-ketose-isomerase.
A classic example of ring opening and contraction is the isomerization of glucose (an aldehyde with a six-membered ring) to fructose (a ketone with a five-membered ring). The conversion of D-glucose-6-phosphate to D-fructose-6-phosphate is catalyzed by glucose-6-phosphate isomerase , an intramolecular oxidoreductase .
Azomethine ylide. Azomethine ylides are nitrogen-based 1,3-dipoles, consisting of an iminium ion next to a carbanion.They are used in 1,3-dipolar cycloaddition reactions to form five-membered heterocycles, including pyrrolidines and pyrrolines.
Azoles are a class of five-membered heterocyclic compounds containing a nitrogen atom and at least one other non-carbon atom (i.e. nitrogen, sulfur, or oxygen) as part of the ring. [1] Their names originate from the Hantzsch–Widman nomenclature .
These conformers can interconvert with one another; however, each form may have very different relative energy, so a significant barrier to interconversion may be present. The energy of these conformations can be calculated from quantum mechanics; an example of possible glucopyranose interconversions is given. [5]
Therefore, the ring distorts slightly to adopt a minimum energy conformation that reduces the unfavorable eclipsing interactions. There are two puckered conformations exist for five-member ring systems. Such conformations include the envelope (IHIPOE, ACUHUB) and the half-chair (LISLOO, ABIKUR); please refer to figure at right.