Molecular formula, determination by mass

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 ... 

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 previously determined (38) molecular formula was corrected to C16H22N4O3 by quantitative elemental analysis and a molecular weight determination by mass spectrometry. 

A compound with the molecular formula C7///JNO3, determined by mass spectrometry, was isolated from the plant Petiveria alliacea (Phytolaccaceae). What is its structure given the set of NMR results 52 ... 

The molecular formula of a compound shows the actual number of each kind of atom present in a molecule of the compound. To work out the molecular formula of a compound, we need to know both the empirical formula and the relative molecular mass of the compound. The latter can be determined by mass spectrometry (see p. 73). 

The chemical makeup of a substance is described by its percent composition—the percentage of the substance s mass due to each of its constituent elements. Elemental analysis is used to calculate a substance s empirical formula, which gives the smallest whole-number ratio of atoms of the elements in the compound. To determine the molecular formula, which may be a simple multiple of the empirical formula, it s also necessary to know the substance s molecular mass. Molecular masses are usually determined by mass spectrometry. 

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). 

An organic compound was prepared containing at least one and no more than two sulfur atoms per molecule. The compound had C and H, no N, but O could have been present. The molecular mass of the predominant nuclidic species was 110.020 u, as determined by mass spectrometry. What is the molecular formula of the compound ... 

Rationalization of known compounds provides a level of usefulness that justifies the rule. But the rule also permits observed molecular stoichiometries of newly synthesized compounds to be translated into acluster shape. For example, [Al Bu ]2-has eve = 50 or sep =13 consistent with n = 12 and a deltahedral structure. The compound has been synthesized and an X-ray diffraction study reveals an icosahe-dral shape. The ability to suggest reasonable structures based on knowledge of a molecular formula generated by a technique like mass spectrometry accelerated the development of cluster chemistry simply because rapid spectroscopic methods can be more productively applied. Although efficient X-ray crystallographic structure determination reduces its importance for compounds that can be isolated in pure crystalline forms, transient intermediates detected in a reaction mixture can now be given reasonable structures. 

A substance with the molecular formula CnH2o04, as determined by mass spectrometry, was isolated from the light petroleum extract of the Chilean medicinal plant Centaurea chilensis (Compositae) 8 mg were available for the set of NMR experiments 45. Beyond the shift range shown in (c), the C NMR spectrum shows the signals of quaternary C atoms at 170.1,169.2,149.8,142.9 and 137.5 ppm. A CH COLOC plot was not recorded owing to shortage of material and time. It was nonetheless possible to identify the natural product which was already known. What is its structure ... 

The molecular formula of villalstonine, earlier presumed to be C40H50N4O4, was subsequently corrected to C41H48N4O4 on the basis of the molecular weight (660) determined by mass spectrometry (28). 

At one time, the molecular weight of a compound was determined by its vapor density or its freezing-point depression, and molecular formulas were determined by elemental analysis, a technique that determined the relative proportions of the elements present in the compound. These were long and tedious techniques that required relatively large amounts of a very pure sample. Today, molecular weights and molecular formulas can be rapidly determined by mass spectrometry from a very small amount of a sample. 

The coupled NMR spectrum (Fig. 6b) and the DEPT subspectra (Fig. 8c, d) for unequivocal detection of CFf multiplicities (C, CH, CH2, CH ) show that acanthifo-lin contains six non-protonated (Ce), four CH (C4//4), three CH2 (CsHe) and four CHs carbon atoms (04 12). These fragments ( Ce + C4H4 + C He + C Hn ) sum up to the CFf partial elementary composition CnH22 (Table 9, p. 164) in accordance with the molecular formula CnH220i, determined by mass spectrometry. In conclusion, no OFf group is present in the molecule. 

The exact molecular weight of pimaricin 73 (Scheme 73) (as the iV-acetyl derivative) was determined by mass spectrometry of its tri-methylsilyl derivative, which was sufficiently volatile and thermally stable. A revised structure for the antibiotic is based on such studies (107). The mass spectra of 0-trimethylsilyl pimaricin and several of its derivatives correspond to a molecular formula of C88H47N07 for pi-... 

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. 

I One of the first steps in determining molecular structure is establishing the molecular formula. In the past, this task was most commonly done by elemental analysis, combustion analysis to determine percent composition, molecular weight determination, and so forth. More commonly today, molecular weight and molecular formula are determined by mass spectrometry (Chapter 14). In the examples that follow, we assume that the molecular formula of any unknown compound has already been determined, and we proceed from that point using spectral analysis to determine a structural formula. 

The determination of molecular formulas via accurate mass measurements relies on isotopic masses accurate to at least 1 in 10 [10]. Elemental trace analysis is required for the detection of radioactive nuclides in the environment, of transition metals such as Pt in exhaust fumes from automobiles [11], and in the quality control of low-sulfur fuels for the same. All electronic devices demand for high-purity semiconductors and the properties of alloys are critically influenced by trace elements [12]. Age determinations from isotope ratios are applied in archeology, paleontology, and geology [4,13,14]. More recently, elemental MS and biomedical MS are jointly employed to unveil the presence and preferably location of metals in proteins or DNA as well as their lateral distribution in tissues [15-18], a field of research basically going back to seminal work by Houk in 1980... 

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