Formula determination

Amongst products isolated from Heliotropium spathulatum (Boraginaceae) were 9 mg of a new alkaloid which gave a positive Ehrlich reaction with p-dimethylaminobenzaldehyde The molecular formula determined by mass spectrometry is CisH2sNOs. What is the structure of the alkaloid given the set of NMR results 54 Reference is useful in providing the solution to this problem. Conditions CDCI3, 9 mg per 0.3 ml, 25 °C, 400 MHz ( //), 100 MHz ( C). (a) HH COSY plot ... 

To determine the molar mass of a substance, we need its chemical formula and elemental molar masses. From the chemical formula, determine the number of moles of each element contained in one mole of the substance. Multiply each elemental molar mass by the number of moles of that element, and add. 

The chemical formula of a compound contains essential information about its composition. The formula identifies which elements are present, and it states the number of atoms of each kind present in one unit of the compound. We need the chemical formula of a substance to calculate its molar mass. In fact, almost all chemical calculations require the correct chemical formula. How are chemical formulas determined in the first place ... 

P.C. Jurs, B.R. Kowalski and T.L. Isenhour, Computerized learning machines applied to chemical problems. Molecular formula determination from low resolution mass spectrometry. Anal. Chem., 41 (1969)21-27. 

The most important advantages of MIP-AES as an analytical technique for GC detection of metals and metalloids are indicated in Table 7.32. MIP-AES is one of the most powerful analytical tools for selective detection in GC, and is potentially quantitative [331]. Elemental figures of merit for GC-MIP detection have been reported [332]. Microwave-induced plasmas have found much greater use in GC than in HPLC interfacing. Reviews on empirical and molecular formula determination by GC-MIP have been published [332,333]. 

Empirical formula determination dependent on elemental response factors... 

Using the approximate formula weight of the simplest formula, determine the true molecular formula and the exact molecular weight. 

The ordered listing of the chemical compounds in Table A2 is the same as that in the JANAF tables and is alphabetical according to the chemical formula with the lowest order letter in the formula determining the position. The thermochemical tables have the following order ... 

X-Ray analysis of the cytisine alkaloid dehydroalbine did not confirm the structural formula determined earlier, and the compound was renamed de-... 

Determination of vitamin A and E in infant milk-based formulae Determination of carotenoids in pumpkins... 

Accurate mass determination using techniques such as peak matching is a reliable way to obtain the empirical formula. Knowledge of the accurate mass to four or five decimal places (see Table 16.1) allows the elemental composition of the compound to be obtained. Before the use of computer algorithms, empirical formula determination was made with the help of Beynon tables. Currently, data systems propose the most probable empirical composition for a given mass. The types of elements suspected to be in the compound can be input into the algorithm to reduce calculation time. 

For the following structural formulas, determine which represent the same compound and which do not. 

If the demand for capacity exceeds the spare capacity available, actual available capacity is to be distributed according to a formula determined by the operator.20 However, the owners enjoy certain preferential rights when capacity is scarce. An owner has relative priority for its needs up to twice its equity interest in the network.21... 

This formula determines the sign of the dipole moment. According to the present assumptions, the sign of the adsorption dipole would be determined by the difference of the work function of the metal and the Mulliken electronegativity of the atom to be adsorbed. 

In recent years the application of electrospray ionization (ESI) mass spectrometry, quadrupole time-of-flight (QqTOF) mass spectrometry, and Fourier transform ion cyclotron resonance (FT-ICR) are used for further structural characterization of DOM (Kujawinski et al., 2002 Kim et al., 2003 Stenson et al., 2003 Koch et al., 2005 Tremblay et al., 2007 Reemtsma et al., 2008). MS/MS capabilities provide the screening for selected ions, and FT-ICR allows exact molecular formula determination for selected peaks. In addition, SEC can be coupled to ESI and FTICR-MS to study different DOM fractions. Homologous series of structures can be revealed, and many pairs of peaks differ by the exact masses of -H2, -O, or -CH2. Several thousand molecular formulas in the mass range of up to more than 600 Da can be identified and reproduced in element ratio plots (O/C versus H/C plots). Limitations of ESI used by SEC-MS are shown by These and Reemtsma (2003). 

The above formulae determine the elongational viscosity coefficient... 

Taylor (10) also showed that high resolution was possible with FAB and that it could be applied to ions as large as these vitamins. However, higher resolution at high masses becomes essential, not for empirical formula determination (which for metal containing systems is often done better by a fit to the isotopic abundance patterns), but simply to be sure of resolving nominal masses as the molecules studied get heavier. 

M. Krachler, T. Prohaska, G. Koellensperger, E. Rossipal, G. Stingeder, Concentrations of selected trace elements in human milk and in infant formulas determined by magnetic sector held inductively coupled plasmaDmass spectrometry, Biol. Trace Elem. Res., 76(2) (2000), 97D112. 

For each of the following molecular formulas, determine the number of elements of unsaturation, and draw three examples. 

Dry air at 80°F (300 K) and 150 psia (1034 kPa) flows at the rate of 500 ft3/min (0.24 m3/s) through a 4-in schedule 40 pipe from the discharge of an air compressor. What is the flow rate in pounds per hour and the air velocity in feet per second Using the Fanning formula, determine the pressure loss if the total equivalent length of the pipe is 500 ft (153 m). 

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