July 22, 1922] 



NA TURE 



117 



the structure of graphite must he derivable from that 

 of the diamond by separating to nearly double their 

 previous distance the sheets of atoms parallel to one 

 of the cleavage planes of the latter crystal. The 

 question has been very carefully considered more 

 recently by Hull in America and by Debye and Scherrer 

 on the Continent in the hope of finding more exactly 

 the details of the movement : they do not quite agree. 



Naphthalene 

 Anthracene 

 Naphthalene . 

 Anthracene « 



OA = a. 

 8-34 



= BOC = oo°, = COA = I22° 49', -y = AOB=90° 

 = BOC=90°, |3=C0A=I24° 24', y = AOB=90°. 



Fig. 2 represents the change as described by Hull. 

 The bonds between the atoms in each sheet are un- 

 affected apparently, but those between sheet and sheet 

 are replaced by something much weaker. The diamond 

 is typical of hardness, the graphite is used as a lubricant. 

 If the hexagonal rings of which the sheets are formed 

 have survived this violent change, why not suppose 

 that they may survive the further change when the 

 sheets break up into ring structures ? In other words, 

 suppose that the benzene ring is really a fact, not merely 

 a diagram ; the distance between atom and atom in 



. 2. — The fine lines of the diagram show the structure of graphite. By 

 moving the top layer to the position shown by the broken lines the 

 diamond structure is obtained. 



the ring is 1-54 A.U. as in the diamond, and perhaps, 

 we may add that the atoms are not all in one plane, 

 but are arranged, as may be seen in Fig. 3. We 

 then proceed to test this hypothesis by finding whether 

 we can fit together molecules of the assumed size and 

 shape into the cells which hold them. From X-ray 

 studies we know the exact form and dimensions of 

 the cells, and can learn also much concerning the 

 relative distributions of the molecules within them. 

 It appears at once that in the few simple cases which 

 have been examined an excellent fit is possible and,, 

 more than that, we find encouraging signs that the 

 structural idea has been chosen rightly. For instance, 

 the comparison of the cells of naphthalene and anthra- 

 cene, one a two-ring, the other a three-ring combination, 



NO. 2751, VOL. I io] 



shows that two of the axes of the cell remain constant 

 while the third has grown by an amount which is nearly 

 the width of the benzene ring. From these and various 

 other indications we build a structure such as is repre- 

 sented in Figs. 3 and 4. It would seem that the 

 molecules are linked together side to side more strongly 

 than from end to end, and that is why these and similar 

 crystals cleave across the end or ji position. 



Fig. 3. — Showing mutual relations of three naphthalene molecules 

 and parts of others. 

 The unshaded circles between the two cleavage planes represent a molecule 

 as at Q (Fig. i). The shaded represent molecules B and F in the same 

 figure. The small circles represent hydrogen atoms, but their size is un- 

 certain. 



Diameter of carbon atom=i-so. BH = ^gz. Projection of AD on the 

 plane of the diagrams 2-50. Benzene ring consists of atoms A . . . F only. 



If we examine a-naphthol in which hydrogen at the 

 side of the naphthalene molecule has been replaced by 

 an OH group, we find that the standard cell contains 

 four molecules, which is what we should expect, for each 

 of the four «. positions must be represented. When 

 the OH group is taken from the side and put at the 

 end, we find that the cell has shrunk sideways and 

 grown lengthways by the amount we should expect 

 to result from the addition of an oxygen atom. When 

 as in acenaphthene a complex group of atoms is 

 attached to one side of the molecule and the crystal 



Fig. 4. — Section of naphthalene cell perpendicular to the axis of c, 

 showing a-hydrogens connecting the molecules side to side. 



to our surprise becomes more regular than before, 

 right angled instead of oblique, we find an explanation 

 in the fact that there are now four molecules within 

 the cell instead of two, and that by sloping in pairs in 

 opposite ways they increase the symmetry of the 

 crystal. 



These examples may serve to show how an attempt 

 may be made to arrive at a knowledge of the structure 

 of these organic compounds with, I think, some success. 

 It seems justifiable to see in the rigid and queerly 

 shaped molecule attaching itself at definite points, 

 and with great precision of orientation to neighbouring 

 molecules, a cause of the immense multiplicity and, at 

 the same time, the accurate form of organic crystals, 

 and indeed to find here the foundations of organic 

 chemistry. 



