September 14, 1939

Professor Arthur B. Lamb, Editor

Journal of the American Chemical Society

Chemical Laboratory of Harvard University

12 Oxford Street

Cambridge, Massachusetts

Dear Professor Lamb:

I have read Dr. Pirenne's remarks concerning his manuscript with interest, and I make the following comments.

Dr. Pirenne writes that no disagreement appeared to exist among the specialists at the Baltimore Meeting as to the main points of his paper, I have found on inquiry that the opinion of some of the specialists there was close to that which I hold (that Dr. Pirenne has pointed out the existence of a situation which is generally recognized, but has made no positive contribution toward its resolution), but that this was not brought out in discussion to save time, the symposium being far behind schedule because of the failure of speakers to stop at the warning signal.

The principal criticism cast at the electron-diffraction result for methyl chloride by Dr. Pirenne is that the correct C-H distance and bond angles and the Z-f factors and temperature factor should have been used in the calculations. Although it was obviously his way to show that these corrections might have made a significant change in the interpretation of the photographs, he did not calculate the corrected curves. I have now made the effort of examining curves calculated for C-H = 1.09 Å end angle H-C-Cl = 104°, 108°, and 112°, using the Z-f and temperature factors, and having found that the three curves are practically identical with one another and with the curve calculated by the method used by Sutton and Brockway in their original determination of the C-Cl distance as 1.77 Å. The revision in the calculation would not change the distance by as much as one percent.

This removes significance from all but one of Dr. Pirenne’s remarks about methyl chloride. His remaining remark is that Sutherland’s x-ray result differs from the electron-diffraction result; this was pointed out by Sutherland himself, and Pirenne has nothing now to say about the discrepancy.

It is possible that the calculation of a series of revised curves for methylene chloride would lead to change in the parameters for this molecule. Since Dr. Pirenne has calculated only one curve, without varying the Cl-C-Cl bond angle, he can not say whether or not the change would be appreciable. I have not gone to the labor of making these calculations.

Dr. Pirenne states on page 3 of his rebuttal that the conclusion reached in his manuscript is that some accepted electron-diffraction measurements need reconsideration. This is recognized by electron-diffraction workers- re-investigations by the improved methods now available have been published recently for several substances studied in the early electron-diffraction days, leading to small revision in the molecular parameters.

As mentioned by Referee II, all of the points made by Dr. Pirenne are well known and have been published before. The only novel feature of Dr. Pirennes’s manuscript is his unsupported contention that the revised methods of calculation might lead to very great changes in results for molecules such as methyl chloride and methylene chloride. This is not substantiated by the results of the execution of the program of calculation for methyl chloride suggested by Dr. Pirenne. I feel more strongly than before that Dr. Pirenne’s manuscript should not be accepted for publication in the Journal.

I wish to point out that Dr. Pirenne’s paper can not lead to a polemic (as he suggests in his rebuttal), because there is no argument about the validity of most of his remarks, but only about their novelty. The one doubtful remark which he makes, that the use of the revised method of calculation would lead to large changes in the electron-diffraction values of the molecular parameters of methyl chloride and methylene chloride, should not be allowed to give rise to a polemic, since it can be easily verified or disproved. I have now disproved the statement so far as it relates to methyl chloride.

I recommend again that the paper be not accepted for publication.

Yours Truly,

Linus Pauling