Excess energies of the electron-impact induced dissociation of several oxygen-containing compounds have been estimated by measuring the translational energies of the fragment ions. The heats of formation of CH30, CzH50, CH3C0, HCO, COOH, and their positive ions have been determined. The forrnyl radical has a heat of formation of 8 f . 3 kcal/mole. Ions of composition CH30+ and C2H50+ from these compounds always have the hydroxy carbinyl structure at threshold energies. The method is shown to be competitive with the best methods of chemical kinetics for determining bond dissociation energies.
SynopsisThe new technique of differential viscometry measures directly the specific viscosity of a solution by subtracting the contribution of solvent in a balanced capillary bridge. The present work adapts the differential viscometry principle to the design of a viscosity detector for use in size-exclusion chromatography. It is shown that the resulting viscosity detector possesses excellent sensitivity and baseline stability with a minimum detectable specific viscosity of 2.7x The viscosity detector can be operated together with a refractive index detector to determine the intrinsic viscosity of polymer solute fractions as they elute from the SEC column.The bandspreading of the viscosity detector is compared to the refractive index detector by measuring the peak width of a compound having a single discrete molecular weight. The peak width at half-height was 0.29 mL for the viscosity detector and 0.25 mL for the refractive index detector.
SynopsisA new type of solution viscometer is described that measures the specific viscosity directly. This is accomplished with a balanced network of four capillaries arranged in a manner analogous to a Wheatstone bridge. A differential pressure transducer measures the increase in pressure across the bridge when a solution is injected into one of the capillaries while solvent flows continuously in the other three capillaries. The differential pressure is proportional to the specific viscosity of the solution. The differential viscometer is about 10 times more sensitive than a conventional glass tube viscometer, permitting precise measurements of specific viscosities of 0.01 or less. The measurements are also inherently fast, averaging about 3 min per sample. Precision is about 1% RSD. Accuracy was investigated by running standard solutions of sucrose in water, polystyrenes in toluene, and polyethylenes in decalin. The agreement was within 2-3% of the standard values in most cases.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.