István Hargittai

Molecular geometry of bis (N-chloromethyl)nitramine from gas electron diffraction

Abstract The molecular structure of bis ( N -chloromethyl) nitramine has been determined by gas electron diffraction. The bond lengths ( r g ), bond angles and angles of torsion (φ) with estimated total errors in parentheses are as follows: Nue5fbO 1.216(3) A Nue5f8N 1.422(5) A Cue5f8N 1.443(4) A Clue5f8C 1.803(4) A Cue5f8H 1.109(9) A ONO 128.0(14)° CNN 116.3(4)° CNC 124.8(9)° ClCN 111.6(5)° HCN 110.3(9)° φ CN 78.9(7)° φ NN 2.6(15)° The amine nitrogen has an essentially planar bond geometry. This molecule has practically C 2 symmetry. The two Clue5f8C bonds point to opposite sides of the planar C 2 NNO 2 skeleton.

Gas-Phase Electron Diffraction for Molecular Structure Determination

Gas-phase electron diffraction is a unique source of structural information on free molecules. The present introduction gives a brief overview of the technique.

Structural Investigation of Molecules of Energetic Materials in the Gas Phase

Recently, Gilardi and Karle (1991) published a review on structural investigations of energetic materials in the crystalline state. The purpose of the study was to promote the understanding of the relationship between structure and function and to facilitate the synthesis of new materials. This study was based on the Cambridge Structural Database (Allen et al., 1983) and also on the Energetic Materials Structural Database of the (U.S.) Naval Research Laboratory (NRL) with over 300 relevant structures (Gilardi et al., 1992).

Linear, Bent, and Quasilinear Molecules

There are unambiguously linear and unambiguously bent molecules, and in between, there are also molecules that possess a flat potential energy minimum in the vicinity of the linear configuration and can be best described as quasilinear. All three structure types can be found among the alkaline earth dihalides as concluded both from quantum chemical calculations and experimental joint electron diffraction/vibrational spectroscopic analyses. The consequences of large-amplitude motion may be substantial on the experimentally determined bond lengths which are thus expected to be larger than the equilibrium bond lengths. Experimental bond lengths of increased accuracy have been compared recently with computed bond lengths for floppy metal halide molecules and the computed values seem to be too large.

Symmetry breaking symmetry

Scarcely any term connects art and science more closely than symmetry. This was already a theme in ancient times, as is found in Vitruvius, for example. On the beach of an unknown island, a shipwrecked traveler finds neatly arranged geometric figures. Can he conclude from this that there is an intelligent creator (perhaps even a god)?

Symmetry and Structure

Symmetry considerations are all-important in studying structures. This compilation provides examples in diverse areas of structural science.1 The examples include molecular symmetry, buckminsterfullerene, the Jahn-Teller effect, chirality and dissymmetry, the double helix and other biological macromolecules, molecular packing in crystals, and quasicrystals