Isomers by mass and molecular formula

A hydrocarbon is 90% carbon by mass and 10% hydrogen by mass and has a molar mass of 40 g-mol It decolorizes bromine water, and 1.46 g of the hydrocarbon reacts with 1.60 L of hydrogen (measured at STP) in the presence of a nickel catalyst. Write the molecular formula of the hydrocarbon and the structural formulas of two possible isomers. 

By far, mass spectrometry (MS) is the most popular detection technique for performing chromatographic studies of essential oils. The use of retention indices, in conjunction with GC/MS studies, is well established. Many laboratories use such procedures in their routine analyses to confirm the identities of unknown components. The identification of components is usually performed by comparing the mass spectra with an MS library. However, a feature of MS for essential oils is that mass spectra are not particularly unique in many cases because of the large numbers of isomers of the same molecular formula, but with different structures, that could exist. Therefore their mass spectra are similar and... 

For nonpolar substances with the same molar mass, the strength of the dispersion forces is influenced by molecular shape. Shapes that allow more points of contact have more area over which electron clouds can be distorted, so stronger attractions result. Consider the two five-carbon alkanes, pentane (also called n-pentane) and 2,2-dimethylpropane (also called neopentane). These isomers have the same molecular formula (C5H,2) but different shapes. n-Pentane is shaped like a cylinder, whereas neopentane has a more compact, spherical shape, as shown in Figure 12.16. Thus, two n-pentane molecules make more contact than do two neopentane molecules. Greater contact allows the dispersion forces to act at more points, so n-pentane has a higher boiling point. Figure 12.17 summarizes how to analyze the intermolecular forces in a sample. 

The molecular formulas of PMs (Table 9.5) obtained by high-resolution mass spectrometry in collaboration with Prof. Y. Kishi, Harvard University, indicate that PMs are formed by the condensation of three molecules of PS and two molecules of methylamine, with the removal of four water molecules. No study has been made on their conformational isomers. 

The substances are ordered by molecular formula in a modified Hill order, in which all substances not containing C (carbon) inorganic substances) are listed alphabetically before those that do contain C organic substances). The relative molar mass (molecular weight) M based on the lUPAC table of standard atomic weights (2005) and the primary names of all the isomers (substances having the same molecular formula) are also given (pp. 4-2 to 4-10). 

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