Symmetry Properties Of Molecules Research Articles

An Inquiry-Based Learning Approach to the Introduction of the Improper Rotation–Reflection Operation, Sn

Symmetry properties of molecules are generally introduced in second-year or third-year-level inorganic or physical chemistry courses. Students generally adapt readily to understanding and applying the operations of rotation (Cn), reflection (σ), and inversion (i). However, the two-step operation of improper rotation–reflection (Sn) often provides a greater challenge for students. Sn operations can be difficult to identify and visualize, and the reason their inclusion in the different types of symmetry operations is not always clear or explained. In this contribution, an inquiry-based learning exercise is used to introduce students to the Sn operation: The results of all symmetry operations are first listed by simple permutations of atoms, and then students search for operations to bring about these permutations.

On symmetry properties of molecules

It is well known to associate an Euclidean graph to a molecule. Balasubramanian computed the Euclidean graphs and their automorphism groups for benzene, eclipsed and staggered forms of ethane and eclipsed and staggered forms of ferrocene [see Chem. Phys. Lett. 232 (1995), 415]. In this Letter, we proved an algorithm, which is useful for finding symmetry of molecules. Using this algorithm, a new simple method is described, by means of which it is possible to calculate the automorphism group of weighted graphs. We apply this method to compute the symmetry of the smallest fullerene C 20. Finally, an upper bound for the order of automorphism group of weighted graphs is obtained.

Vibration rotation Raman spectroscopy of gas media

A method using the symmetry properties of molecules has been developed for describing high resolution Raman spectra. This method can be applied to spontaneous Raman scattering and to nonlinear Raman scattering or resonance Raman spectroscopy. A high sensitivity laser Raman spectrometer has been constructed and some weak vibration rotation bands of diatomic molecules have been observed. The polarizability functions of N 2 and O 2 are determined. The laser spectrometer has been used for gas diagnostics.

Chemical combinatorics. Part 3.—Stereochemical invariance law and the statistical mechanics of flexible molecules

The replacement of three-dimensional molecular models by one-dimensional molecular graphs is a simplifying feature of many physical and chemical theories, particularly for mixtures. For this to be a sound procedure in statistical mechanics, one requires an explicit invariance law relating symmetry properties of molecules in three-, two- and one-dimensional states. This law is here derived. Although it is simple, it reveals a surprising property of Euclidian spaces and their subspaces. The law articulates the statistical mechanical treatment of systems of molecules which are flexible by virtue of bond rotation, in a manner complementary to the treatment of fluids with interparticle forces by the theory of irreducible cluster graphs. The law can be generalised to rigid bond systems, but with some loss of generality. It completes the rigorous analysis of the statistical basis of gelation, which is important for the understanding of living systems.