Chemical substance In organic chemistry, there can be more than one chemical compound with the same composition and molecular weight. Generally, these are called isomers. Isomers usually have substantially different chemical properties, and often may be isolated without spontaneously interconverting. A common example is glucose vs. fructose. The former is an aldehyde, the latter is a ketone. Their interconversion requires either enzymatic or acid-base catalysis. However, tautomers are an exception: the isomerization occurs spontaneously in ordinary conditions, such that a pure substance cannot be isolated into its tautomers, even if these can be identified spectroscopically or even isolated in special conditions. A
NASA Star and Exoplanet Database public data to support the search for and characterization of extra-solar planets (exoplanets) and their host stars. The data include published light curves, images, spectra and parameters, and time-series data from surveys that aim to discover transiting exoplanets. All data are validated by the NStED science staff and traced to their sources. NStED is the U.S. data portal for the CoRoT mission. As of December 2011, SDtED is no longer in operation. Most data and services have been transferred to the NASA Exoplanet Archive. Data are searchable either for an individual star or by stellar and planetary properties. NStED offers