Galactopyranose conformation

Problem 25,13 Draw /3-o-galactopyranose and jS-D-mannopyranose in their more stable chair conformations. Label each ring substituent as either axial or equatorial. Which would you expect to be more stable, galactose or mannose ... 

Draw /3-t-galactopyranose in its more stable chair conformation, and label the substituents as either axial or equatorial. 

A disaccharide of related structure, namely, 2-acetamido-2-de-oxy-3-0-(4-deoxy-a-L-ffireo-hex-4-enopyranosyIuronie acid)-a-D-galactopyranose, has been studied143 at 60 and 100 MHz, and the conformation 53 proposed for it. The presence of N-acetyl signals of... 

All substituents, except for the -OH at C4, are equatorial in the more stable conformation of p-L-galactopyranose. 

One reason is that the conformation moves significantly away from the classic chair shape. This is what we see with the bis-ketal 2.10, diacetone-galactose (l,2 3,4-di-O-isopropylidene-a-D-galactopyranose). It has been drawn as an ordinary alicyclic compound in order not to prejudge its conformation. 

Although there is some uncertainty as to the conformational effect of one cis-fiised, 5-membered acetal ring, evidence from both i.r.-and n.m.r.-spectral studies clearly indicates that the presence of two such cis-fiised rings forces the cyclohexane or pyranoid ring to adopt a skew conformation. Thus, the pyranoid ring in derivatives of 1,2 3,4-di-0-isopropylidene-j3-L-arabinose and -a-D-galactopyranose (34), and of 2,3 4,5-di-0-isopropylidene-/3-D-fructopyranose (35), and the... 

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