July 30, 1931

Dr. Arthur B. Lamb,

Chemical Laboratory of Harvard University

12 Oxford Street

Cambridge, Mass.

Dear Professor Lamb:

I believe that Dr Huggins’ note is not suitable for publication in the Journal, inasmuch as there is very little evidence supporting the structures he suggests, and a strong theoretical argument against them. Hence I suggest that the note be returned him with a copy of my remarks. You need not keep my identity secret – it would be difficult to do anyway, since the note and letter from you were sent to me by Dr. Huggins himself, who had received them through the mail.

1. The evidence supporting the structure with three double bonds is that it has the proper symmetry. But ^:O: _:O::N:O:^- has the correct symmetry also, when the quantum mechanical electron distribution is examined, for the single-bond axis is a cylindrical symmetry axis. Moreover, the structure ^:O: _:O::N::O:^- with the double bond jumping from one oxygen to another has the correct symmetry, has also an ionic structure.

2. The quantum mechanics requires that only four electron pairs occupy the L shell. Hence although P and Cl and other heavier atoms may form more than four bonds, C, N, O may not, unless the much weaker eigenfunctions in outer shells are brought into play. This result, that atoms in the first row of the periodic system can form not more than four electron pair bonds, is a useful and important rule with no exceptions that I know of, and in my opinion electronic structures which are in disagreement with it are not acceptable.

3. This argument also can be used against the suggested structures for the nitro and carboxyl groups. The symmetry and the small proton-attraction are equally well explained by a structure containing one single bond and one double bond, the two changing places rapidly in accordance with the resonance phenomenon.

I shall be pleased to review the Strukturbericht. Would you let me know also at what price the book is sold?

Very truly yours,

Linus Pauling

LP:L