2016年4月21日 · If you have exactly one asymmetric carbon with inverted stereochemistry, then the diastereomer is a special one: an epimer. Anomers (e.g. α- and β-D-glucose) should be considered special cases of epimers. Let me use the menthol isomers (image taken from Wikipedia, where a full list of authors is available) to clarify the concept:

2018年8月28日 · IUPAC basic terminology of stereochemistry defines anomers and epimers:. Anomers. Diastereomers of glycosides, hemiacetals or related cyclic forms of sugars, or related molecules differing in configuration only at C-1 of an aldose, C-2 of a 2-ketose, etc.

2017年5月20日 · The three structures below all have the same molecular formula and the same connectivity, but differ in the absolute configuration at a single stereocentre (this is the definition of an epimer). You can see that glucose and galactose are epimeric at the $\mathrm{C4}$ position, whilst glucose and mannose are epimeric at the $\mathrm{C2}$ position.

2022年9月26日 · The $\ce{C2}$ epimer of D-glucose is D-mannose wherein the -OH group at $\ce{C2}$ is axial. Now your right hand structure has some issues. It is a heptapyranoside as shown in structure 3a given the configurations in your structure with the addition of the configuration at the anomeric carbon based upon what your structure displays.

2020年1月5日 · Open-chain carbohydrates are a good example (compare D-glucose, L-glucose, D-galactose, D-talose etc.). For this class of molecules, there is one more term, epimer (when exactly one chiral centre is switched). This generalization excludes the more exotic cases of stereoisomers, see e.g.

2015年4月5日 · There are a number of types of rapid chemical equilibria that basically cannot be turned off. Tautomers are probably the best known examples, although fluxional behavior is observed in many inorganic and organometallic systems.

2019年6月8日 · $\begingroup$ Of course the product can be protonated. It can also form an enol. It is just that the enol of the product is less prevalent than the enol of the starting material, and so if you only have a limited amount of bromine to react, …

2016年1月26日 · Additional explanation. D-L system (also called Fischer–Rosanoff convention) is mainly used for naming α-amino acids and sugars.

2016年11月9日 · $\begingroup$ Thanks, that site is very useful. Well my issue was how to determine if the lowest priority groups in a Haworth were into or out of the page (as when writing R or S, we've always had to put the lowest priority group into the page).

2013年12月11日 · $\alpha$-D-glucose and $\beta$-D-glucose are stereoisomers - they differ in the 3-dimensional configuration of atoms/groups at one or more positions.