Mass molecular structures

The hardening of a phenolic resin can be seen as the transformation of molecules of different sizes via chains lengthening, branching, and crosslinking to a three-dimensional network with theoretically an endlessly high molar mass. The hardening rate depends on various parameters, such as molar mass, molecular structure of the resin, the portions of various structural elements as well as possible catalysts and additives. 

Characterization techniques were used to determine molecular mass, molecular structure, morphology, thermal as well as mechanical properties. Various techniques commonly used for characterization of PHB include FTIR,NMR, DSC,TGA, GPC, and AFM. 

Correlation of Mass Spectra with Molecular Structure 7.123... 

Some mild methods of ionization (e.g., chemical ionization. Cl fast-atom bombardment, FAB electrospray, ES) provide molecular or quasi-molecular ions with so little excess of energy that little or no fragmentation takes place. Thus, there are few, if any, normal fragment ions, and metastable ions are virtually nonexistent. Although these mild ionization techniques are ideal for yielding molecular mass information, they are almost useless for providing details of molecular structure, a decided disadvantage. 

Metastable ions yield valuable information on fragmentation in mass spectrometry, providing insight into molecular structure. In electron ionization, metastable ions appear naturally along with the much more abundant normal ions. Abundances of metastable ions can be enhanced by collisionally induced decomposition. 

The steps (reactions) by which normal ions fragment are important pieces of information that are lacking in a normal mass spectrum. These fragmentation reactions can be deduced by observations on metastable ions to obtain important data on molecular structure, the complexities of mixtures, and the presence of trace impurities. 

The importance of linked scanning of metastable ions or of ions formed by induced decomposition is discussed in this chapter and in Chapter 34. Briefly, linked scanning provides information on which ions give which others in a normal mass spectrum. With this sort of information, it becomes possible to examine a complex mixture of substances without prior separation of its components. It is possible to look highly specifically for trace components in mixtures under circumstances in which other techniques could not succeed. Finally, it is possible to gain information on the molecular structures of unknown compounds, as in peptide and protein sequencing (see Chapter 40). 

Typical MS/MS configuration. Ions produced from a source (e.g., dynamic FAB) are analyzed by MS(1). Molecular ions (M or [M + H]+ or [M - H]", etc.) are selected in MS(1) and passed through a collision cell (CC), where they are activated by collision with a neutral gas. The activation causes some of the molecular ions to break up, and the resulting fragment ions provide evidence of the original molecular structure. The spectrum of fragment ions is mass analyzed in the second mass spectrometer, MS(2). 

By measuring a mass spectrum of normal ions and then finding the links between ions from the metastable ions, it becomes easier to deduce the molecular structure of the substance that was ionized originally. 

Molecular ion. An ion formed by the removal (positive ions) or addition (negative ions) of one or more electrons from a molecule without fragmentation of the molecular structure. The mass of this ion corresponds to the sum of the masses of the most abundant naturally occurring isotopes of the various atoms that make up the molecule (with a correction for the masses of the electrons lost or gained). For example, the mass of the molecular ion of the ethyl bromide CzHjBr will be 2 x 12 plus 5 x 1.0078246 plus 78.91839 minus the mass of the electron (m ). This is equal to 107.95751p -m, the unit of atomic mass based on the standard that the mass of the isotope = 12.000000 exactly. 

Coumarin, 3,4-dihydro-4-phenyl-synthesis, 3, 848 Coumarin, 6,7-dihydroxy-molecular structure, 3, 622 Coumarin, 7,8-dihydroxy-molecular structure, 3, 622 Coumarin, 6,7-dimethoxy-mass spectra, 3, 610... 

Coumarin, 6-ethoxycarbonyl-4,5,7-trihydroxy-synthesis, 3, 805-806 Coumarin, 3-hydroxy-Mannich reaction, 3, 680 mass spectra, 3, 609 Coumarin, 4-hydroxy-alkylation, 3, 692 azo dyes from, I, 331 electrophilic substitution, 2, 30 IR spectra, 3, 596 Mannich reaction, 3, 680 mass spectra, 2, 23 3, 609 molecular structure, 3, 622 reactions... 

Selenophene, 2-methylmercapto-conformation, 4, 944 Selenophene, 2-nitro-mercuration, 4, 946 Selenophene, 2-phenyl-irradiation, 4, 42, 946 mass spectra, 4, 942 Selenophene, 3-phenyl-mass spectra, 4, 942 Selenophene, tetrachloro-applications, 4, 971 reactions, 4, 955 synthesis, 4, 963 Selenophene, tetrahydro-conformation, 4, 34, 944 IR spectra, 4, 942 mass spectra, 4, 24, 943 molecular structure, 4, 938 NMR, 4, 10, 13 reactions, 4, 88, 958 ring strain, 4, 28 synthesis, 4, 118, 962, 968 Selenophene, tetraphenyl-synthesis, 4, 118, 962, 964 Selenophene, 2-thienyl-... 

Heat Capacity, C° Heat capacity is defined as the amount of energy required to change the temperature of a unit mass or mole one degree typical units are J/kg-K or J/kmol-K. There are many sources of ideal gas heat capacities in the hterature e.g., Daubert et al.,"" Daubert and Danner,JANAF thermochemical tables,TRC thermodynamic tables,and Stull et al. If C" values are not in the preceding sources, there are several estimation techniques that require only the molecular structure. The methods of Thinh et al. and Benson et al. " are the most accurate but are also somewhat complicated to use. The equation of Harrison and Seaton " for C" between 300 and 1500 K is almost as accurate and easy to use ... 

Fullerenes are described in detail in Chapter 2 and therefore only a brief outline of their structure is presented here to provide a comparison with the other forms of carbon. The C o molecule, Buckminsterfullerene, was discovered in the mass spectrum of laser-ablated graphite in 1985 [37] and crystals of C o were fust isolated from soot formed from graphite arc electrodes in 1990 [38]. Although these events are relatively recent, the C o molecule has become one of the most widely-recognised molecular structures in science and in 1996 the codiscoverers Curl, Kroto and Smalley were awarded the Nobel prize for chemistry. Part of the appeal of this molecule lies in its beautiful icosahedral symmetry - a truncated icosahedron, or a molecular soccer ball, Fig. 4A. 

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