Glucose conformational formulas

Structure of cellulose, (a) /3(1 4) linkage of glucose residues in cellulose, (b) Conformational formula... 

Studies of the structures of the cyclic hemiacetal forms of D-(-+-)-glucose using X-ray analysis have demonstrated that the actual conformations of the rin are the chair forms represented by conformational formulas 6 and 7 in Fig. 22.3. This shape is exactly what we would expect from our studies of the conformations of cyclohexane (Chapter 4), and it is especially interesting to notice that in the j8 anomer of D-glucose all of the large substituents, —OH and —CH2OH, are equatorial. In the a anomer, the only bulky axial substituent is the —OH at Cl. 

From contemporary X-ray diffraction work, it is known that the real structure of D-glucose is as shown in (/j./p), which preserves the outlines of the saturated ring (13.2) and records the conformation (Section 13.3) which this particular example has been found to adopt. Although this conformational formula is much nearer to the truth than are the earlier representations, most people find that it takes longer to draw. 

Haworth formulas are satisfactory for representing configurational relationships in pyranose forms but are uninformative as to carbohydrate conformations X ray crystal lographic studies of a large number of carbohydrates reveal that the six membered pyra nose ring of D glucose adopts a chair conformation... 

Vanillin (4-hydroxy-3-methoxybenzaldehyde), the principal component of vanilla, occurs in vanilla beans and other natural sources as a /3-D-glucopyranoside. Draw a structural formula for this glycoside, showing the D-glucose unit as a chair conformation. 

In the most stable conformation of free sucrose in the solid state (formula A in Fig. 3) the terminal positions of both sub-units are close to each other. It is a result of strong hydrogen bonds between 6 -OH and ring ojygen atom of the glucose part and I -OH and 2-OH. 

---