23 September 1953

Dr. J. Jennen

Gevaert Photo-Producten

Mortsel, Antwerp

Belgium

Dear Dr. Jennen:

I am sorry to say, in answer to your letter of 7 September, that I do not have any reprints left of my 1939 article in the Proceedings of the National Academy of Sciences.

I doubt that the conclusion reached by Bates and Hobbs, in their 1951 paper in the Journal of the American Chemical Society, is justified. I may point out that their own conclusion, as stated in italics, is not unambiguous! they say "either because of its absence or of contributions from a compensating polar structure, the usual polar resonance form written for the amides makes a very small or negligible contribution to the structure of the amide group." I judge that their use of the words "or of contributions from a compensating polar structure" means that they are discussing in fact only the electric dipole moment of the amide group, and not the structure, and that the foregoing statement made by them means that the observed dipole moment agrees with a moment calculated by them with neglect of the usual polar resonance form either because the usual polar resonance form does not make a contribution to the dipole moment or because there is some compensating effect that accidentally causes them to find agreement. In any case, I am sure that their work does not justify one to say that the usual polar resonance form is unimportant. Other evidence, far more reliable, indicates clearly that this structure makes a large contribution, and, in fact, that the contribution can be estimated to be about 40 percent in case that the amide group is forming hydrogen bonds, and somewhat smaller, perhaps 30 percent, if it is not forming hydrogen bonds.

Sincerely yours,

Linus Pauling:W