Molecular cation

Some of the target molecules gain so much excess internal energy in a short space of time that they lose an electron and become ions. These are the molecular cation-radicals found in mass spectrometry by the direct absorption of radiation. However, these initial ions may react with accompanying neutral molecules, as in chemical ionization, to produce protonated molecules. 

Low molecular cationic polymers or alum can also be used to flocculate pitch, ie, bind up the pitch so that it is retained in the sheet, to minimize pitch deposition on machine surfaces and fabrics (35,36). Alum is used commonly in newsprint operations (34). The addition of a nonionic surfactant with a hydrocarbon solvent to the wet end has shown some utility in preventing deposits of adhesive recycled furnish contaminants from forming on the paper... 

Tlie molecular cation radical of 2-(3,5-di-f-butyl-4-oxopheiiyl)-l,3-dithiolaiie (59), which was generated by the electron impact method, split into ethylene and the cation radical of the corresponding dithiirane 60 (79DOK1030). 

Macropolycyclic ligands, 2,942 classification, 2,917 metal complexes binding sites, 2, 922 cavity size, 2,924 chirality, 2, 924 conformation, 2,923 dimensionality, 2, 924 electronic effects, 2, 922 shaping groups, 2,923 structural effects, 2,922 molecular cation complexes, 2,947 molecular neutral complexes, 2,952 multidentate, 2,915-953 nomenclature, 2,920 Macro tetrolide actins metal complexes, 2,973 Macrotricycles anionic complexes, 2,951 cylindrical... 

To summarise, a fractionation step allows the isolation of the compounds of interest from the other molecular constituents, particularly from the fatty acids that are well-ionised. To compensate for the low ionisation yield of some compounds, such as TAGs, the solutions may be doped with a cation. Samples are then directly infused into the ion electrospray source of the mass spectrometer. A first spectrum provides an overview of the main molecular compounds present in the solution based on the peaks related to molecular cations. The MS/MS experiment is then performed to elucidate the structure of each high molecular compound. Table 4.2 shows the different methods of sample preparation and analysis of nonvolatile compounds as esters and TAGs from reference beeswax, animal fats and archaeological samples. 

Fig. 5 (a) Structure directing agent (SDA) in the synthesis of zeolite ITQ-3 N quaternary nitrogen A-I carbon atoms of SDA, l,3,3,6,6-pentamethyl-6-azonium-bicyclo[3.2.1]octane some 13C line assignments were not unequivocally possible, so these are left open the orientation of the dipole moment was calculated with a semiempirical AM-1 simulation with the origin at the center of gravity of the molecular cation (b) 13C H 27A1 REAPDOR experiment on synthetic zeolite ITQ-3. Adapted from [204]... 

What shape would an early transition-metal hydride adopt if the ionic component were reduced Structural analysis of the cation HfH3+ (which is isovalent with LaH3) provides insight. The molecular cation exhibits bond angles (98.1°) that are nearly 10° less than those of LaH3, even though the Hf—H bond ionicity (lOOcHf2 = 36.35%) still deviates appreciably from the covalent limit. 

Figure 13.19 summarizes the reaction mechanism starting from Sn(OH) + or Sn(OH)e in acidic media in alkaline media. As in the case of Pd, Sn02 oxide is spontaneously formed by dehydration due to an internal oxolation reaction promoted by a strong polarization of the O-H bond of the hydroxide. Thermodynamically stable species with respect to pH are presented in Fig. 13.20. Various molecular cationic species with different hydroxylated levels are possible in an acidic medium, whereas only Sn(OH)g is expected for a basic pH.

In the second case the covalent =Si-0-M bond should be substituted by an ionic-type [=Si-0] M bond. Under these conditions, the support will play the role of an heterogeneous non-coordinating anion, which should stabilize the floating molecular cation above the surface. 

MNDO calculation of AH for 3-amino-1,2,4-dithiazole-5-thione indicated that, of its possible isomeric forms (7), (8), and (9) (R = H), (7) is the most favorable. This structure had been found experimentally in the crystal and in solution but the differences are small and structures (8) and (9) may also take part in reactions. In fact, methylation of (7 R = H) gives (9 R = Me) shown by MNDO calculation to possess the lowest AHf <82JCR(S)65>. The MNDO method was used to calculate the structure and energy of 3-amino-1,2,4-dithiazole-5-one, its molecular cation and also its fragmentation ions <82MI 4i3-oi>. 

They have bactericidal activity against gram negative bacteria only and are low molecular cationic polypeptide antibiotics. 

Considerable attention has been devoted to the study of intercalation compounds of the dichalcogenides (Whittingham, 1978 Subba Rao Shafer, 1979). Intercalation compounds of dichalcogenides can be divided into three categories (a) compounds with Lewis base type molecules such as ammonia, n-alkylamines, pyridines etc. (b) compounds with metal cations or molecular cations, Li, Na, K, etc., or [(C5H5)2Co]" and (c) compounds containing both cations and neutral polar (solvated) molecules in the van der Waals gap. 

Bracketed number would be the molecular cation if mass spectrometry is used for quantification... 

In Ag[cis-Pt(NH3)2(l-methylthymine)2]2N03 5H20, the molecular cation (10) consisted of two units connected by a silver cation via the exocyclic 0-4 atoms. The Ag—O bond distances were in the range 235.3-256.3 pm.97... 

For [(NH3)8Pt4(l-methyluracil)4Ag]5+ (II), the molecular cation showed crystallographic centrosymmetry with Ag being at the inversion centre. The silver atom thus had square planar coordination with four 0-2 oxygens of 1-methyluracil ligands, two from each platinum dimer. The Ag—O bond distances in this case were 243 and 235 pm, and the Pt—Ag separation was 278.7 pm. 

Historically, the concept of coordination chemistry was associated with complexation of a metal cation (Lewis acid) by a ligand behaving as a Lewis base. Such was traditionally the case for macrocyclic molecules as ligands. In the early 1970s, however, the concept of coordination chemistry was extended in the area of macrocyclic chemistry to include molecular cations, neutral molecules and anions as substrates. Complexes of all of these species are to be included in the scope of this chapter section. Examples of the types of substrates are discussed below. 

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