The Molecular Structure of Organic Compounds

1965 the Chemical Abstracts Service began assigning a registry number to each new substance reported. The total number of classified chemical compounds has now passed 25 million, and about 95% of these substances are organic. About 4,000 new substances are registered each day. 

2 Given Lewis diagrams, ball-and-stick models, or space-filling models of two or more organic molecules with the same molecular formula, distinguish between isomers and different orientations of the same 

Element Number of Bonds Molecular Bond Geometry  

Carbon 4 1 Tetrahedral 109.5° angles / Trigonal Planar 120° angles Linear 180° angle —C= Linear 180° angle 

Nitrogen 3 A Trigonal pyramidal structure Ns / Angular structure N= 

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It is important to note that the molecular structure of organic compounds has a determined effect on the oxidation rate constants. For example, if a compound is "saturated" with four chlorine atoms per carbon atom such as tetrachloroalkane, its reactivity rate with hydroxyl radicals is expected to be significantly lower than that of an "unsaturated" compound with only two or three chlorine atoms such as di- and trichloroalkanes. 

Gavezzotti, A. (1994b). PROMET3. A program for the generation of possible crystal structures from the molecular structure of organic compounds. University of Milano, available upon request. [183, 186]... 

A. Gavezzotti, PROMET "A Program for the Generation of Possible Crystal Structures from the Molecular Structure of Organic Compounds , A. Gavezzotti, J. Am. Chem. Soc. 1991, 113, 4622. 

If the objective is identification (qualitative analysis), it suffices to compare the spectrum of the analyte with that of a standard, both recorded in the same solvent and at an identical pH. This is not the main application of UV-Vis spectrophotometry as the best results in this context are provided by spectroscopic methods considered more effective for the study of the molecular structure of organic compounds (infrared, nuclear magnetic resonance, mass spectrometry, and X-ray diffraction). However, UV-Vis spectrophotometry is a source of relevant supplementary information that helps in the elucidation of molecular structures of drugs, impurities, metabolites, intermediate compounds of degradation, etc. 

More recently especially Brown and Shaw [63], Dave and Patel [64]. Gray [65, 66], de Jeu et al. [67], Kast [68] and Wiegand [69] have done much work in the field of liquid crystalline phases and have investigated the relationship between the molecular structure of organic compounds and the occurrence of anisotropic mesophases. Survey reports concerning this theme were given especially by L. Creagh [70] and R. Steinstrasser and Pohl [71]. Kast [72] listed all compounds known up to 1959 with liquid crystalline properties. 

As mentioned earlier, NMR is a very valuable method for obtaining information regarding the molecular structure of organic compounds with any number of protons. The electronic environment, as well as near neighbours and stereochemistry, can be determined by analysing the chemical shifts and spin-spin couplings of protons. The relative number of protons can be determined by direct integration of the areas under the peaks (multiplets), as the number of protons is directly proportional to the area under the peaks produced by those protons. To obtain... 

Mass spectrometry and DD. In mass spectrometry (MS), decomposition consists in fragmentation and ionization of molecules under the action of electron flux. The same process of fragmentation and ionization of multielement phases takes place also in the case of DD. This process runs in solutions of acids when a solid substance is subjected to the action of the proton flux (both protons and electrons are the elementary particles). The role of vacuum in MS is similar to the role of pure solvent in DD. These are the media that contain fragments of molecules and phases prepared for separation. And finally, similar to reconstruction of the molecular structure of organic compounds from fragments in MS, stoichiometric formulas of inorganic compoimds are found from stoichiograms in DD. 

Beyond the considerations of the molecular structure of organic compounds, synthesis has played a vital role in much more fundamental theoretical... 

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