Determining Molecular Formulas

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 ... 

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]. 

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). 

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

The Structural identification of (-)-6a-hydroxylupanine was based on the analysis of its spectral data and is in full agreement with the C15H24N2O4 molecular formula determined by HRMS [219]. The mass fragments at m/z 247 [M-OH] and m/z 246 [M-H20] suggested the presence of a hydroxyl substituent, further confirmed by an IR absorption band at 3400 cm". Further analysis of the IR spectrum also provided evidence for the quinolizidine nucleus (2860, 2810 and 2750 cm, tram Bohlmann absorption bands) and the oxo substituent (1640 cm, lactam group). 

The (+)-13a-hydroxyaphyllidine structure was proposed on the basis of the C15H22N2O2 molecular formula determined by HRMS, IR absorptions at 3270, 1635 and 1560 cm (suggesting the presence of hydroxyl, lactam and ethylene functions), and also of the UV spectrum which indicates a vinyl amide group (A ax 239 nm). The position of the hydroxyl group was assessed by comparison of the C NMR data of (+)-13a-hydroxyaphyllidine and aphyllidine, which showed similar resonances for the carbon atoms of rings A, B, and C, and also by... 

The starting point for mass spectrometric characterizations is often the determination of the molecular weight. If the impurity arose after exposure to oxygen and a mass shift of 16 is observed between the drug substance and the impurity, it can be concluded that the impurity is oxidized drug substance. High mass accuracy mass spectrometry may also be used for molecular formula determination. 

This rapid molecular formula determination may also be applied to complex mixtures such as those which arise from combinatorial chemistry.To demonstrate the performance of this method in this respect, a split-mix compound collection of 140 different pyrrole amides consisting of 10 subcollections of 14 compounds each was synthesized on Rink-amide-AM-resin. 

Ring formation in hydrocarbons can account for unsaturation. As the carbon-carbon single bond is formed, two hydrogens are lost. In other words, when an alkane gives rise to a cycloalkane, two hydrogens are lost from the original molecular formula determine how many... 

Fortunately, some of the weaknesses may be overridden by using better hardware. Thus, higher mass resolution helps in molecular formula determination (Sections 8.7 and 8.8). Additional spectroscopic analyses (e.g. AAS, AES) provide additional information for element composition determination if available, e.g. the empirical formula (cf. Definition 1.25). Under such circumstances the molecular formula determination is unambiguous in many cases. 

In agreement with our previous considerations of MMD, an unambiguous determination of molecular formula is ensured for a precision of d > 5 decimal places for 4. For 11 there are cases in our sample where molecular formula determination is ambiguous even for 6 decimal places. In the extreme case there are 153 possible molecular formulas within this interval, although the 3rd quartile (Table 8.19) indicates that the majority of formulas can be unambiguously determined at 6 decimal place precision. 

Based on the molecular formula, determine whether the noncyclical hydrocarbons are alkanes, alkenes, or alkynes. 

Based on the molecular formula, determine whether each compound is an alkane, alkene, or alkyne. (Assume that all the compotmds are noncyclic and do not contain more than one multiple bond.) (a) C4H6 (b) C6H14 (c) CsHu (d) C11H22 36. Based on the molecular formula, determine whether each compoimd is an alkane, alkene, or alkyne. (Assume that all the compoimds are noncyclic and do not contain more than one multiple bond.) (a) C3H6 (b) CeHio (0 C3H8 (d) C5H10... 

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