Microwave spectroscopy, and

High accuracy molecular dimensions for the planar parent heterocycles in the gas phase have been obtained by microwave spectroscopy and are recorded in Table 2. These values have been corroborated for furan by a low-temperature X-ray crystallographic study... 

Dioxolane also pseudorotates essentially freely in the vapor phase. 2,2 -Bi-l,3-dioxolane (128) has been shown by X-ray crystallography to have a conformation midway between the half-chair and envelope forms. The related compound 2-oxo-l 3-dioxolane (129) shows a half-chair conformation. This result is confirmed by microwave spectroscopy and by NMR data. Analysis of the AA BB NMR spectra of the ring hydrogen atoms in some 1,3-dioxolane lerivatives is in agreement with a puckered ring. Some 2-alkoxy-l,3-dioxolanes (130) display anti and gauche forms about the exocyclic C(2)—O bond. 

The geometries of oxiranes have been determined mainly by X-ray diffraction on crystalline natural products, the oxirane ring being widespread in nature (Section 5.05.5.3). However, the detailed structure of the parent compound (Figure 1) has been secured by microwave spectroscopy and electron diffraction studies (64HC(l9-l)l). The strain in this... 

Experimental (Microwave Spectroscopy)" and Calculated Molecular Structures OF THE Parent 1, 2-Dithiete (241)"... 

The S-S bond between two divalent sulfur atoms plays an important role as the main stabilizer of the tertiary structure of many proteins. The simplest chemically stable compounds of this class are HSSH and CH3SSCH3. The structures of these two disulfanes have been established by microwave spectroscopy and electron diffraction experiments. 

Caminati, W., A. C. Fantoni, L. Schafer, K. Siam, and C. Van Alsenoy. 1986. Conformational and Structural Analysis of Methyl Hydrazinocarboxylate by Microwave Spectroscopy and Ab Initio Geometry Refinements. J. Am. Chem. Soc. 108,4364 1367. 

Nakata, M., H. Takeo, C. Matsumura, K. Yamanouchi, K. Kuchitsu, and T. Fukuyama. 1981. Structures of 1,2-Dimethylhydrazine Conformers as Determined by Microwave Spectroscopy and Gas Electron Diffraction. Chem. Phys. Letters 83, 246-249. 

Nakata, M., H. Takeo, C. Matsumura, K. Yamanouchi, K. Kuchitsu, andT. Fukuyama. 1981. Structures of 1,2-Dimethylhydrazine Conformers as Determined by Microwave Spectroscopy and Gas Electron Diffraction, Chem. Phys. Letters 83, 246-249. Norden, T. D., S. W. Staley, W. H. Taylor, and M. D. Harmony. 1986. On the Electronic Character of Methylenecyclopropene Microwave Spectrum, Structure, and Dipole Moment, J. Am. Chem. Soc. 108, 7912-7918. 

I was working at Bell Telephone Laboratories at that time. Much of the radar development came out of applied work in industrial laboratories, and so did microwave spectroscopy. I persuaded the Bell Laboratories to let me do microwave spectroscopy, and so it started at Bell Labs, but it also started at General Electric, where a friend of mine began it. He did a little bit of work, but then the General Electric people said, no, you must stop, it s not going to have any use for us, we have no applications. So this work had to stop at General Electric. At RCA, another important electrical company, a friend of mine started it there, and he worked on it for a while, and the company said, no, that s of no value to us, we won t pay you anything for it, you must stop. 

Bell Telephone Laboratories asked me to stop, because they said, look, there are some engineering things that we d like you to do that would be much more important to us. But I didn t want to do that, and I said, look, I really want to do some physics, and they let me do it. And I continued to do microwave spectroscopy, and pretty soon microwave spectroscopy was interesting enough to other physicists that I got a job at Columbia University. And so I moved to academia because industry wasn t all that interested in the field. 

The techniques available to achieve molecular structure determinations are limited. They include structural analysis with diffraction techniques—such as electron, neutron, and x-ray diffraction—and various absorption and emission techniques of electromagnetic radiation—such as microwave spectroscopy and nuclear magnetic resonance (NMR). For molecules with unpaired spins a companion technique of electron spin resonance spectroscopy (ESR) is highly informative. 

The accurate spatial location of these atoms generally needs a sophisticated approach, for example, the study of a complete deuterated set of isotopic derivatives in microwave spectroscopy or the use of neutron diffraction techniques. We shall see below that a set of CNDO/2 calculations combined with suitable experiments (microwave spectroscopy and/or electron diffraction) may help to solve the geometrical and conformational analysis of compounds containing many hydrogen atoms. 

The purpose of this brief survey was to demonstrate that, despite the criticisms which may be made of the use of any semi-empirical quantum technique for structural and conformational studies, the CNDO/2 and Extended CNDO/2 formalisms are definitely reliable tools for theoretical conformational analyses in inorganic and coordination chemistry. Moreover, if these tools are combined with the most suitable experimental techniques (i.e. microwave spectroscopy and electron diffraction) in that field, many problems of geometry and conformation can be solved in a way that neither of these approaches could have accomplished alone. 

H. Mpllendal, Structural and conformational properties of 1,1,1 trifluoro 2 propanol investi gated by microwave spectroscopy and quantum chemical calculations. J. Phys. Chem. A 109, 9488 9493 (2005). 

The above discussion will be familiar to all physical scientists, especially in the context of microwave spectroscopy and atomic vibrations. We should now consider what would happen if the mass m was in the middle of a long chain and the masses either side were free to move. As the mass moves, the force on the adjacent masses increases until cat = n/2. Following Tabor,6 we can make the approximation that at this point the adjacent masses move in turn and a wave propagates through the material. This gives the wave velocity, vw, as... 

Microwave Region Microwave spectroscopy and electron spin resonance (ESR) (due to absorption) are employed as analytical methods. 

Trioxolanes remain the most studied ring system by microwave spectroscopy and recently, 1,2,4-trithiolane also became the subject of attention. In all cases, isotopically labelled derivatives were made which have very different rotational constants. These aid assignment of structures and also provide useful tools for looking at the mechanism of the ozonolysis reaction. Rotational constants for the parent compounds and their calculated dipole moments are given in Table 3. 

TABLE 5. Comparison of the structural parameters of gaseous 1,2,4-trioxolane determined by microwave spectroscopy and electron diffraction ... 

In CHEC(1984) <1984CHEC(2)1> electron diffraction, microwave spectroscopy, and X-ray analysis of pyridazine and simple derivatives were included. All data are consistent with a planar structure and significant N-N single bond character. CHEC-II(1996) <1996CHEC-II(6)1> contained some additional structural parameters derived from X-ray... 

Equilibrium geometries for upwards of four thousand small molecules have been determined experimentally in the gas phase, primarily by microwave spectroscopy and electron diffraction. In the best cases, the experimental techniques are able to provide bond lengths and angles to within a few thousandths of an A and a few tenths of a degree, respectively. For larger systems, lack of data usually prohibits complete stmcture determination, and some geometrical variables may have been assumed in the reported stmcture. 

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