Nuclear Magnetic Resonance, correlated spectroscopy

Liao. M.-Y. Harbison, G.S. Two-dimensional nuclear magnetic resonance correlation spectroscopy at zero field. J. Chem. Phys. 1999. 111. 3077-3082. 

Crosslinked polymer networks formed from multifunctional acrylates are completely insoluble. Consequently, solid-state nuclear magnetic resonance (NMR) spectroscopy becomes an attractive method to determine the degree of crosslinking of such polymers (1-4). Solid-state NMR spectroscopy has been used to study the homopolymerization kinetics of various diacrylates and to distinguish between constrained and unconstrained, or unreacted double bonds in polymers (5,6). Solid-state NMR techniques can also be used to determine the domain sizes of different polymer phases and to determine the presence of microgels within a poly multiacrylate sample (7). The results of solid-state NMR experiments have also been correlated to dynamic mechanical analysis measurements of the glass transition (1,8,9) of various polydiacrylates. 

Nuclear magnetic resonance (NMR) spectroscopy is routinely applied to small carbohydrate molecules. NMR spectroscopy is based on the principle that radiofrequencies are absorbed by hydrogen and carbon atoms ( H and 13C) spinning in one of two directions (spin quantum number +1 /2) in a magnetic field. In liquids, absorption is recorded as sharp peaks. The frequency displacement (chemical shift) is a function of the H and 1SC surroundings. +A is proportional to the number of photons absorbed between these two quantum states, correlating well with anomeric and... 

In the past decades, nuclear magnetic resonance (NMR) spectroscopy has been used extensively to study various aspects of polymer chemistry and engineering. Fig. 1 shows the relationship among polymerization conditions, polymer structure, and the material s physical structure and end uses. Solution, solid state, and imaging NMR techniques contribute to imderstanding the physical and chemical aspects of the route from raw materials to final product. Solution NMR provides information about all aspects of the polymerization reactions and the final structure of the synthesized polymer. This information can be correlated with the material s final properties and provide feedback to control the initial polymerization process so that the fraction of structures responsible for desirable properties can be controlled in a systematic way. 

For some liquid feedstocks such as naphthas, the componential composition is often obtained by gas chromatography (GC) and/or mass spectrometry (MS). For gas oils or heavier feedstocks, it is impossible to obtain the desired analysis. Paraffins, olefins, naphthenes, aromatics (PONA) grouping is sometimes used as a means of feed characterization. For gas oils. Bureau of Mines Correlation Index (BMCI) has been used as a parameter for feed characterization. Since the 1980s, nuclear magnetic resonance (NMR) spectroscopy has been used to characterize heavy feedstocks. 

Nuclear magnetic resonance (NMR) spectroscopy has great relevance in the area of investigation of molecular structures. Many studies using NMR spectroscopy and microscopy have been reported in elastomer based systems. Due to the possibihty of reuse of samples after the analysis (NMR is nondestructive) NMR attracts many material scientists to select this technique for characterization. In the case of polymers NMR is specifically useful in finding out the crosslink density. Since the crosslink density is related to the size of pores or cavities inside solid polymers, this method points towards the structural elucidation of polymers. From the parameters such as magnetic relaxation and the dipolar correlation effect obtained from the NMR spectrum, crosslink density can be calculated. In addition to the crosslink density, the behaviour of small particles inside the polymer matrices can also be... 

The application of ultraviolet (UV) spectroscopy in the elucidation of the structure of terpenes and other natural products was extensively used by R.B. Woodward in the early forties of the last century. On the basis of his large collection of empirical data, he developed a series of rules (later called the Woodward rules), which could be applied to nding out the structures of new natural substances by correlations between the position of UV maximum absorption and the substitution pattern of a diene or an a,p-unsaturated ketone (Woodward, 1941). He was awarded the Nobel Prize in Chemistry in 1965. However, it was not until the introduction of chromatographic separation methods and nuclear magnetic resonance (NMI spectroscopy into organic chemistry that a lot of further structures of terpenes were elucidated. The almost exponential growth in our knowledge in that eld and other essential oil constituents is essentially due to the considerable advances in analytical methods in the course of the last half century. 

Nuclear magnetic resonance (NMR) spectroscopy is the most informative analytical technique and is widely applied in combinatorial chemistry. However, an automated interpretation of the NMR spectral results is difficult (3,4). Usually the interpretation can be supported by use of spectrum calculation (5-18) and structure generator programs (8,12,18-21). Automated structure validation methods rely on NMR signal comparison using substructure/ subspectra correlated databases or shift prediction methods (8,15,22,23). We have recently introduced a novel NMR method called AutoDROP (Automated Definition and Recognition of Patterns) to rapidly analyze compounds libraries (24-29). The method is based on experimental data obtained from the measured ID or 2D iH,i C correlated (HSQC) spectra. 

When simple Hquids like naphtha are cracked, it may be possible to determine the feed components by gas chromatography combined with mass spectrometry (gc/ms) (30). However, when gas oil is cracked, complete analysis of the feed may not be possible. Therefore, some simple definitions are used to characterize the feed. When available, paraffins, olefins, naphthenes, and aromatics (PONA) content serves as a key property. When PONA is not available, the Bureau of Mines Correlation Index (BMCI) is used. Other properties like specific gravity, ASTM distillation, viscosity, refractive index. Conradson Carbon, and Bromine Number are also used to characterize the feed. In recent years even nuclear magnetic resonance spectroscopy has been... 

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