Experimental evidence for the amino-group non-planarity in nitroanilines: neutron diffraction study of 2-methyl-5-nitroaniline at 100 K

An appreciable degree of pyramidalization of the amine N atom is observed i n the title compound. The existence of polar chains, induced by N-H ... O s ynthons, is confirmed. C-H ... O interactions, not noted in a previous X-ra y study, were found to stabilize further the known head-to-tail assembling of the chains. The structure can be described as non-polar (101) layers, em bodying chains interlinked by centrosymmetric dimers, connected by C(aryl)- H ...pi interactions. The latter are not present in m-nitroaniline, 2-methy l-4-nitroaniline and other related compounds with chains built from similar N-H ... O synthons and assembled head-to-head. This finding implies that a n obvious relationship between molecular recognition patterns and crystal s tructures should not be assumed.