38 FUNDAMENTALS OF SUBMICROSCOPIC MORPHOLOGY I 



however, is not true to reality, since the C-O distance in it is unduly 

 large. Haworth (1925), therefore, writes sugar as an equilateral 

 hexagon or pentagon, according as to whether the oxygen bridge is 

 situated between the carbon atoms 1-5 (derivatives of pyranose) or 



CH=0 

 H><OH 

 HO^H 

 H^OH 

 HxOH 

 CH2OH 

 o) 



C—OH 

 \H 



2 HCOH 



I 



3 HOCH 



HCOH 



I 

 HC 



CH2OH 

 b) 



cj 



dj 



Fig. 35. Glucose, a) Aliphatic, b) heterocj^clic sti-uctural formula; 

 c, d) a- and /^-configuration after Haworth (1925, 1929). 



1-4 (derivatives of furanose). Figs. 35c and d represent the glucose 

 pyranoses. With the aid of the distance rules (see Table III, p. 31), the 

 dimensions of a glucose molecule can be calculated. For example, on 

 the assumption that the ring is completely in one plane and represents 



an equilateral hexagon, the axis drawn through 

 the C-atoms i and 4 has a length of 2 • i . 5 4 + 

 2-1.49 = ^-^^ ^- '^^^^ value is only approx- 

 imate, because, to begin with, the hexagon is 

 not completely equilateral on account of the 

 somewhat smaller diameter of the O-atom, 

 and further, the C-atoms, as well as the OH- 

 groups represented by the O-atoms, do not 

 lie strictly in the plane in which the distances 

 are measured so that, instead of the distances 

 C-C and C-O, only their projections contri- 

 bute to the length concerned. If all this is ta- 

 ken into account, the smaller value of 5.15 A 

 is obtained, which corresponds to that found 

 by X-ray analysis. Fig. 36 shows the far-reaching similarity between 

 the present structural formulae (Fig. 55c) and the molecular models. 

 The former no longer represent arbitrary schemes, but rightly propor- 

 tioned projections of the molecular structure on a plane. 



According to the aliphatic manner of writing (Fig. 35a), glucose 

 contains four asymmetric C-atoms (x), since only the CHo- and the 



Fig. 36. Molecular structure 



of glucose (from Meyer and 



Mark, 1930). C-atomshatch- 



ed, O-atoms encircled. 



