194 LINUS PAULING 



Professor Pitzer: Yes, also in nitromethane. In other words, we have no 

 evidence for a six-fold term exceeding a few small calories. In nitromethane 

 or any other molecule where the two sides of the planar group are the same, 

 the potential is effectively zero. 



Therefore, I think that the best approximation that we can make in the light 

 of the known information is to neglect the six potential minima. In other words, 

 if we can get potential minima and maxima in any significance in this case, it 

 is going to be because the two sides of the planar group are different. If these 

 two sides are different, then the significant potential term remaining is the 

 three-fold term, not the six. 



The first conclusion that we can reasonably draw is that there should be three 

 minima rather than six. Secondly, the three-fold term arises from the difference 

 between the sides of the molecule and whichever has the weaker interaction 

 will line up and whichever has the stronger interaction will stagger between 

 the three bonds at the other end. 



I also wish to make a remark about the solubility cjuestion. Repeating just 

 about what Pauling said, the solubility changes by roughly a factor of 10 if 

 you change the energy term by a kilocalorie or TAS by a comparable amount. 

 It does not make any difference whether it is a big molecule or a little molecule, 

 the relation between energy and solubility product is the same. 



Consider two large molecules which fit together nicely. If an oxygen atom is 

 added and the molecules do not fit, the energy may change so as to decrease 

 the solubility considerably. Or similarly, the energy might change by a kilo- 

 calorie the other way. 



On the other hand, here we have an example of the failure of a crystal struc- 

 ture to accommodate itself to the molecular geometry. We were remarking 

 earlier that it always did seem to accommodate itself and that we never find 

 crystals in which molecules are in strained configurations. But within, now, an 

 even finer scale, we do find appreciable shifts in solubility because in one case 

 the molecule accidentally, as it were, fits better with the oxygen in and in 

 another case it fits a little better with the oxygen out. 



Chairman Pauling: Thank you for pointing this out. If I understand cor- 

 rectly, you think that only if the double bond is in the cis position to one of 

 the single bonds of the other group in the peptide do you have stability. 



Professor Pitzer: Yes, and I think that it is almost certain that the car- 

 bonyl lines up with the bond at the other end. 



Chairman Pauling: Then if I remember the alpha helix correctly, the ori- 

 entation around the C — C single bond is right, and that around the alpha car- 

 bon to nitrogen bond is wrong. I shall have to examine that point. 



Professor Jehle: A somewhat different problem which puzzled me often 

 is the question of the structure of the DNA when it is incorporated into a small 

 compact virus particle. One might think of it as being composed of chopped- 



