Via Chemical Abstracts it is easy to get an overview of all 352 scientific articles that were published by Backer. Publication of the big majority of the articles took place in Receuil des Travaux Chimiques des Pays-Bas (et de la Belgique) usually briefly designated with Recueil. It is clear that there were several research topics in which he was interested for quite some years. Besides that his wide interest in research topics stood out. Even though Backer was a synthetic chemist, he was not afraid of applying physical chemistry techniques. This is a remarkable fact, especially in the first half of the twentieth century. He measured acid dissociation constants and kinetic parameters, applied Hammett substituents constants and incorporated crystallography in his research as early as 1931. Furthermore, he had a clear interest in pharmaceuticals (e.g. steroids and vitamins) and in molecules with extraordinary structures such as globular shapes. During his career he had a special interest in organic sulfur chemistry like sulfones, sulfinic acids, sulfenyls, sulfur-containing heterocycles, and especially carbonic acids modified with sulfur or selenium atoms. Between 1948 and 1954 he published over 44 articles in Recueil with the title “Properties of the Sulfonyl Group”. But also before he reported a series of systematic studies into the chemistry of sulfonyl compounds, under which the addition of sulfur dioxide to butadiene and related structures. This interest was clearly passed on to the next generations of researchers in Groningen: the synthetic chemists Strating, Zwanenburg, Van Leusen and the physical-organic chemist Engberts. Early in his career he was in particular interested in nitroso compounds, which was an interest that lasted until he retired. One of the highlights was the work of Thymen de Boer in 1954 affording a more efficient preparation of diazomethane. This important building block was prepared in high yield by decomposition of p-tolylsufonylmethylnitrosamide under basic conditions, which is nowadays still in use.
The work of Backer was further renowned by its thoroughness and reliability. After his death many of Backers publications were cited multiple times.