Pyranose rings are often drawn in a chair conformation like cyclohexane rings (Section 4-6) with substituents being either an axial or equatorial position. Pyranose rings are even capable of undergoing a ring flip to change between chair conformations.

Convert the Haworth to a chair conformation if needed. The groups pointing “up” in a Haworth stay “up” in the chair and “down” stay down (either axial or equatorial). Putting this together in a three-step process, here is a guide you can use in the practice problems below for converting Fischer projection to Haworth and Chair forms:

Different chair conformations interconvert spontaneously in solution, and the rate of interconversion is very rapid. More stable conformations orient bulky groups in equatorial (eq) rather than axial (ax) positions (excluding substituents at the anomeric carbon where stereoelectronic effects occur).

Draw the two chair conformations of the sugar called mannose, being sure to clearly show each non-hydrogen substituent as axial or equatorial. Predict which conformation is likely to be more stable, and explain why.

During ring cyclization, two potential isomers can form, either the alpha conformation or the beta conformation. In the alpha configuration, the functional groups extending from the carbons attached to the ring oxygen (the –OH of carbon‐1 and the CH2OH group

Chair conformations 6-membered (pyranose) rings exist in a chairconformationbecause of the angles on the sp 3 -hybridized carbons. Let’s take the example of D-glucose (a D-aldohexose).

configuration at their anomeric carbons Organic Lecture Series 16 Haworth Projections • Haworth projections – five- and six-membered hemiacetals are represented as planar pentagons or hexagons, as the case may be, viewed through the edge – they are most commonly written with the anomeric carbon on the right and the hemiacetal oxygen to

β-D-Glucopyranose in a chair conformation Note. The hydrogen atoms bonded to carbon are frequently omitted, but their inclusion may be necessary to make a stereochemical point.

It is shown on its most stable form, a 5-atom ring or furanose: fructofuranose. the anomeric carbon. Extension: configuration of the beta anomer. #1 corresponds to the convention for defining alpha = downwards and beta = upwards: the …

Fructose has a cyclic or chair-like structure. The chair form of fructose is similar to that of glucose, but in the structure of fructose, there are a few exceptions. Fructose has a ketone functional group, and the ring closure occurs from the 2 nd carbon position.