Parent ions

The base peak in the mass spectrum of the LM free metal-ligand ion and the fragmentation patterns of this parent ion are of particuliar significance since they illustrate the effect of coordination upon the properties of the thiazole ligand. The free thiazole fragments upon electron impact by two major routes (Scheme 86 also cf. Section II. 6). 

Several relationships aid in deducing the empirical formula of the parent ion (and also molecular fragments). From the empirical formula hypothetical molecular structures can be proposed, using the entries in the formula indices of Beilstein and Chemical Abstracts. 

Natural Isotopic Abundances. The relative abundances of natural isotopes produce peaks one or more mass units larger than the parent ion (Table 7.75a). For a compound C H O N, a formula allows one to calculate the percent of the heavy isotope contributions from a monoisotopic peak, Pto the Pm + 1 peak ... 

Fixed-product ion scans (sector instruments). High-voltage scan or linked scan at constant B /E. Both techniques give a spectrum of all precursor (parent) ions that fragment to yield a preselected product (daughter) ion. 

Constant neutral loss (or fixed neutral fragment) scans. The linked scan at constant B[1 -(E/Eg)] /E gives a spectrum of all product (daughter) ions that have been formed by loss of a preselected neutral fragment from any precursor (parent) ions. 

Daughter ion. An electrically charged product of a reaction of a particular parent ion. In general, such ions have a direct relationship to a particular precursor ion and, indeed, may relate to a... 

Parent ion. An electrically charged molecular moiety that may dissociate to form fragments, of which one or more may be electrically charged, and one or more are neutral species. A parent ion can be a molecular ion or an electrically charged fragment of a molecular ion. 

Rearrangement ion. An electrically charged dissociation product, of a molecular or parent ion, in which atoms or groups of atoms have transferred from one portion of the molecule or molecular moiety to another during the fragmentation process. 

The combined techniques of gas chromatography/mass spectrometry (gc/ms) are highly effective in identifying the composition of various gc peaks. The individual peaks enter a mass spectrometer in which they are analyzed for parent ion and fragmentation patterns, and the individual components of certain resoles are completely resolved. 

The most common modes of operation for ms/ms systems include daughter scan, parent ion scan, neutral loss scan, and selected reaction monitoring. The mode chosen depends on the information required. Stmctural identification is generally obtained using daughter or parent ion scan. The mass analyzers commonly used in tandem systems include quadmpole, magnetic-sector, electric-sector, time-of-flight, and ion cyclotron resonance. Some instmments add a third analyzer such as the triple quadmpole ms (27). 

In specialized cases, a treatment known as canonization sometimes is tried to improve the amount of molecular (chemical) information made available. If Ag or Na are deliberately introduced into the sample, they will ofren combine with the molecular species present to create Ag or Na molecular ions. These ions are more stable to fragmentation than the bare molecular ions, and can therefore be observed more easily in the mass spectrum. The identification of parent ion peaks in this manner aids in detailed chemical identification. 

Low ionizing potentials or soft ionization methods are necessary to observe the parent ions in the mass spectra of many S-N compounds because of their facile thermal decomposition. Mass spectrometry has been used to investigate the thermal breakdown of S4N4 in connection with the formation of the polymer (SN). On the basis of the appearance potentials of various S Ny fragments, two important steps were identified ... 

The mass spectra of alcohols often completely lack a peak corresponding to the parent ion. This is due to extremely rapid loss of neutral fragments following initial ionization. For example, the mass spectrum of 2-methyl-2-butanol lacks a parent peak and contains strong peaks at M-15 (loss of CH3O and M-18 (loss of H2O). 

Problem 12.4 1 List the masses of the parent ion and of several fragments you might expect to find in the mass spectrum of the following molecule ... 

Besides a parent ion, the mass spectra of benzo- and dibenzothiepins show the corresponding naphthalene or phenanthrene radical cations as the base peak.2-16 The mass spectra of 1-benzo-thiepin 1-oxides and 1,1-dioxides show the same naphthalene radical cation, formed by loss of sulfur monoxide or sulfur dioxide, respectively.14 In contrast, in the mass spectrum of 2,7-di-terf-butylthiepin peaks resulting from the loss of sulfur are not found.17... 

M represents the mass of the fragment and parent ions and eV is the accelerating voltage. 

Parent ion/precursor ion An ion that undergoes fragmentation to produce a daughter ion and a neutral product. 

Product ion/daughter ion An ion related to a precursor or parent ion by a process such as fragmentation. For example, a parent ion fragments to produce a daughter ion. 

It gives the parent ion in the mass spectrum and has a simple IR spectrum (i (Ru=0) 1040 cm-1 and (i/(Ru—F) 720 cm-1) similar to that of the vapour (1060, 710, 675 cm-1), implying a monomeric structure. Chlorides RuOC12 and Ru2OC1x (x = 5,6) have been claimed various oxo complexes Ru2OX o are well defined. 

Inghram and Corner showed that the mass spectra of molecules were much simpler using a field ionization source than with an electron bombardment ion source. Mainly parent ions are formed, unlike under electron impact which gives rise to considerable fragmentation. The simplicity of the mass spectra offers obvious applications in analysis of complex organic mixtures and their use is likely to become widespread... 

In this context it should be mentioned that some fragmentation data for compounds 127-13152 and 132-14353 have also been given. Compounds 127-131 do not exhibit peaks for the parent ions at all. Their base peaks are m/z 93 (anilinium ion, compounds 127-129) and m/z 172 ([M - R] +, compounds 130-131). 

We also observe other effects of translational energy in methane which are similar to those found in hydrogen. There is an abstraction reaction for parent ions which also produces a hydronated methane. In studying the reaction... 

Mass spectrometric studies yield principally three types of information useful to the radiation chemist the major primary ions one should be concerned with, their reactions with neutral molecules, and thermodynamic information which allows one to eliminate certain reactions on the basis of endothermicity. In addition, attempts at theoretical interpretations of mass spectral fragmentation patterns permit estimates of unimolecular dissociation constants for excited parent ions. 

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