Structure cristalline de la chloroacétamide

The generation of possible crystal structures of primary amides

Procedures are outlined for generation of crystal structures of primary amide molecules by constructing the possible ways in which the molecules may pack. For each given one- or two-dimensional hydrogen-bonded array, ensembles of three-dimensional crystal structures are generated by considering the possible ways in which the arrays may be juxtaposed. Observed and generated hypothetical molecular arrangements are analysed to highlight both favourable and unfavourable features, par­ticularly in terms of close packing principles, the size and shape of the molecule, van der Waals and Coulomb interactions and N-H ∙ ∙ ∙ O bonding geometry.

Diamagnetic anisotropy of some organic molecules

The diamagnetic anisotropies of crystals of aromatic and aliphatic compounds, mostly of known structure, have been measured, and the principal molecular susceptibilities deduced from these and the molecular orientations. In a few cases where the absolute susceptibility is not known with certainty, the molecular anisotropy may, nevertheless, be calculated with a good degree of accuracy. The molecular susceptibilities and anisotropy are related to the molecular shape and constitution, and to the bond character; and in the case of aromatic compounds they are strongly influenced by substitution, which, in general, markedly decreases the anisotropy. This decrease varies not only with the nature of the substituents (heavy atom, compact group or aliphatic chain) but with their positions on the nucleus. This may give some information concerning the effect of substitution on conjugation, especially when correlated with changes in bond lengths and angles.