Molecular formulas, using mass spectroscopy

Mass spectrometry (MS) provides the molecular weight and valuable information about the molecular formula, using a very small sample. High-resolution mass spectrometry (HRMS) can provide an accurate molecular formula, even for an impure sample. The mass spectrum also provides structural information that can confirm a structure derived from NMR and IR spectroscopy. 

Nuclear Magnetic Resonance spectrometry is used for many types of analytical work but is key in the elucidation of structures of chemical compounds. When used in conjunction with mass spectrometry and infrared spectroscopy, the three techniques make it possible to determine the complete structures of novel compounds. Mass spectrometry is used to determine the size of a molecule and its molecular formula and infrared spectroscopy help identify the functional groups present in a molecule. NMR spectroscopy is used to determine the carbon-hydrogen framework of a molecule and works with even the most complex molecules. NMR is now being used to elucidate complicated protein structures ... 

Hufford et al [57] used proton and 13C NMR spectrometric data to establish the novel sulfur-containing microbial metabolite of primaquine. Microbial metabolic studies of primaquine using Streptomyces roseochromogenus produced an A-acety-lated metabolite and a methylene-linked dimeric product, both of which have been previously reported, and a novel sulfur-containing microbial metabolite. The structure of the metabolite as an S-linked dimer was proposed on the basis of spectral and chemical data. The molecular formula C34H44N604S was established from field-desorption mass spectroscopy and analytical data. The 1H- and 13C NMR spectra data established that the novel metabolite was a symmetrical substituted dimer of primaquine A-acetate with a sulfur atom linking the two units at carbon 5. The metabolite is a mixture of stereoisomers, which can equilibrate in solution. This observation was confirmed by microbial synthesis of the metabolite from optically active primaquine. 

Mass spectrometry and IR spectroscopy give valuable but limited information on the identity of an unknown. Although the mass spectral and IR data reveal that X has a molecular formula of C4Hg02 and contains a carbonyl group, more data are needed to determine its complete structure. In Chapter 14, we will learn how other spectroscopic data can be used for that purpose. 

In this scheme, the most computationally time-consuming procedure is the connection of the atoms or substructures to generate structure candidates. We illustrate this scheme via elucidation of the structure of gib-berellic acid (GBA). The molecular formula of gibberellic acid was determined as C19H22O5 from mass spectroscopy. By using a C distortionless... 

Today, a number of different instrumental techniques are used to identify organic compounds. These techniques can be performed quickly on small amounts of a compound and can provide much more information about the compound s structure than simple chemical tests can provide. We have already discussed one such technique ultraviolet/visible (UVA/is) spectroscopy, which provides information about organic compounds with conjugated double bonds. In this chapter, we will look at two more instrumental techniques mass spectrometry and infrared (IR) spectroscopy. Mass spectrometry allows us to determine the molecular mass and the molecular formula of a compound, as well as certain structural features of the compound. Infrared spectroscopy allows us to determine the kinds of functional groups a compound has. In the next chapter, we will look at nuclear magnetic resonance (NMR) spectroscopy, which provides information about the carbon-hydrogen framework of a compound. Of these instrumental techniques, mass spectrometry is the only one that does not involve electromagnetic radiation. Thus, it is called spectrometry, whereas the others are called spectroscopy. 

Solution Mass spectroscopy is a technique used to deter-mine the molecular weight, formula and structure of a compound. It differs from infrared, raman, ultraviolet and nuclear magnetic resonance spectroscopy in that it is a destructive spectroscopy the sample is fragmented by the technique and cannot be recovered in its original form. Mass spectroscopy involves the bombardment of a sample with an electron beam of a particular energy. If the sample is subjected to a low energy electron beam (about 10 eV-electron volts) the molecule will lose an electron to... 

The kind of information available from mass spectroscopy falls into two categories. First, the m/z value for the molecular ion provides information useful in calculating the molecular formula of the molecule. Second, the lower molecular weight fragments that ap >eur in the mass spectrum contain clues concerning structural features of the molecule in question. Be sure that you understand how to extract these kinds of information from muss spectral data. 

The spectra should also be useful to teachers who are not trying to teach all the areas of spectroscopy covered here. In many cases, the mass spectrum can be replaced by a molecular formula, though this substantially increases the difficulty of a few problems. Many C problems can be solved without H, and vice versa, though this will make a few problems too difficult for beginners. 

In the beginning of this chapter, we defined spectroscopy as the study of the interaction between matter and electromagnetic radiation. In contrast, mass spectrometry is the study of the interaction between matter and an energy source other than electromagnetic radiation. Mass spectrometry is used primarily to determine the molecular weight and molecular formula of a compound. 

In Chapter 14 you will team about mass spectrometry, infrared spectroscopy, and UVA is spectroscopy, three instrumental techniques that chemists use to analyze compounds. Mass spectrometry is used to find the molecular mass and the molecular formula of an organic compound it is also used to identify certain structural features of the compound by identifying the fragments produced when the molecule breaks apart. Infrared (IR) spectroscopy allows us to identify the kinds of bonds and therefore the kinds of functional groups in an organic compound. Ultraviolet and visible (UVA is) spectroscopy provides information about compounds that have conjugated double bonds. 

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