29 November 1955

Mr. Hansa Raj Mehta

Central Glass and Ceramic Research Institute

Jadavpur, Calcutta 32

India

Dear Mr. Mehta:

I have read the manuscript that you prepared, and which was sent to me by Dr. Dutta, with much interest.

I have not been able to find anything in your manuscript that changes my opinion about the three-electron bond. This opinion is discussed in detail in my original paper on the three-electron bond, which was published in the Journal of the American Chemical Society, 53, 3325 (1931), and is also discussed in the corresponding chapter in my book. There is a sound quantum mechanical basis for the three-electron bond. It is known that a three-electron bond can be formed between two atoms by use of one orbital for each of the two atoms and of three electrons, and also that the energy of a three-electron bond is only about 60 percent as great as that of an electron pair bond. It is for this reason that the three-electron bond occurs so rarely. For example, a molecule for which a structure might be drawn involving two three-electron bonds should instead, in case that orbitals are available, be assigned a structure with a single bond and a double bond. A single bond and a double bond have about three times as much energy as a single bond alone, whereas two three-electron bonds have only 1.2 times the energy of a single bond. It is true that the single bond and the double bond require six atomic orbitals, whereas the two three-electron bonds require only four orbitals, and a molecule might be discovered in which only four orbitals are available. Nevertheless, this is a rare situation. For example, the structure that you have shown for the nitro group and the ozone molecule, involving two three-electron bonds, is much less stable than a structure in which one single bond and one double bond are shown, with, of course, resonance between the single bond and the double bond.

Now let us discuss the structure that you assign to naphthalene. In this structure there are ten three-electron bonds between carbon atoms, and one single bond. The conventional structures for naphthalene involve five double bonds and six single bonds. If you consider the energy of three-electron bonds, single bonds, and double bonds, you will find that your naphthalene structure is very unstable, relative to the others.

On the second page of your manuscript you give a long discussion of electronic structure in relation to the configuration of the nuclei of naphthalene. This discussion does not have significance because in fact electronic resonance occurs completely in the period of time required/ motion of the nuclei, as explained in the last chapter of my book.

The theory of the structure of aromatic and conjugated molecules has been pretty thoroughly developed by use of semi-empirical quantum mechanical methods, and the agreement between the results of calculations made by different methods (all of them being approximations to the solution of the Schrodinger equation for the molecule) is so good that there remains really no question about the electronic structure of these molecules. I do not think that there is any justification for attempting to introduce three-electron bonds in a discussion of their structure.

Perhaps I should mention one other point. In your paper you suggest a structure for nascent hydrogen. The idea that there exists a special form of hydrogen, nascent hydrogen, has been given up.

I should be pleased to have you write to me about any other ideas that you have.

Sincerely yours,

Linus Pauling:W

cc: Dr. Dutta