An X-ray investigation of certain long-chain compounds

Abstract

The substances which are investigated in this paper have the following chemical formula: CH 3 . (CH 2 ) m A or CH 3 (CH 2) n CH ⋮ CH (CH 2 ) p A. These molecules consist of two parts. One which is called the chain or hydrocarbon-chain contains a relatively large number of CH 2 groups. All these groups are chemically identical ( n -compounds) except those near the unsaturated bond or near the ends of the chain. The other part “A” is a comparatively small radical such as — CH 3 or — COOH or —CH . Br . COOH and is called the end group. Substances with hydrocarbon chains occur very frequently in the organic world. An X-ray investigation of a few typical representatives is likely to supply the key for the crystal structure of a large number of chemically similar substances. Such an investigation is not only interesting from the point of view of stereo-chemistry but also in connection with monomolecular films. Considerable work has been done in recent years on very thin films which these long-chain compounds form on a water surface. Langmuir (1) and later Adam (2) have measured the area occupied by a single molecule in such a film. A corresponding area has been obtained from measurements on a solid crystal by means of X-rays. A comparison of the two data leads to several interesting conclusions. This work was started more than three years ago. It is far from being complete now, but it has reached a stage where a publication does not seem to be premature.