Adduct formation

Mobile phase additives and impurities in the sample solution can add to the complexity of mass spectrum in LC/MS. Noncovalent complexes such as protonated dimeric ions [2M + H ] are common. Other common adduct ions include complex cations ([M -i- [M -i- Na ], [M -i- K ], etc.), solvent adduct 

In Cl plasma, all the ions are liable to associate with polar molecules to form adducts, a kind of gas-phase solvation. The process is favoured by the possible formation of hydrogen bonds. For the adduct to be stable, the excess energy must be eliminated, a process which requires a collision with a third partner. The reaction rate equation observed in the formation of these adducts is indeed third order. Ions resulting from the association of a reagent gas molecule G with a protonated molecular ion MH+ or with a fragment ion F+, of aprotonated molecular ion MH+ with a neutral molecule, and so on, are often found in Cl spectra. Every ion in the plasma may become associated with either a sample molecule or a reagent gas molecule. Some of these ions are useful in the confirmation of the molecular mass, such as 

These associations are often useful to identify a mixture or to determine the molecular masses of the constituents of the mixture. In fact, a mixture of two species M and N can give rise to associations such as (MH + N)+, (F + N)+ with (F + M)+, and so on. Adducts resulting from neutral species obtained by neutralization of fragments, or by a neutral loss during a fragmentation, are always at much too low concentrations to be observed. 

It is always useful to examine the peaks appearing beyond the ions of the molecular species of a substance thought to be pure. If some peaks cannot be explained by reasonable associations, a mixture must be suspected. 

The first spectrum contains the peaks of various adducts of the molecular ion of a pure compound. The second spectrum is that of a substance that is initially pure, as shown by other analysis, but appears as a mixture in the gas phase as it loses either hydrogen cyanide or water. 

In most complexes, the charge transfer band is well separated from the MC band, so that it is easy to obtain excited states of different nature by exciting with radiation of suitable wavelengths. Co(phen)] and Co(bpy) [146] do not present charge transfer absorption bands (LMCT or MLCT) in the visible but only a weak MC band and n-n transitions in the UV. 

Co(phen) and Co(DIP) have been reported to cleave DNA upon irradiation with UV light (k 320 nm) [117,147]. As no mechanistic studies were performed, the different reactions leading to strand scissions are not known. Photoreduction of the Co(III) species could constitute the initial step of the reaction pathway. 

The same stereospecific interaction found with Ru(phen)3 or Ru(DIP)3 enantiomers with DNA of different helicities, has been observed in the photocleavage reactions by the corresponding Co (III) enantiomers, as indicated by the specific cleavage of left-handed DNA by /l-Co(DIP)t [148]. The use of 

CofNHs) also photo-cleaves DNA [117], but in this case, formation of Co (II) and oxidised ligand from the LMCT state could represent an alternative pathway to a direct oxidation, leading to strand scission. 

It has also been reported that Co(III)-bleomycin (or synthetic analogues) cleave DNA when illuminated with UV [151 153]. 

Rate constants for exchange of axial water molecules in the tetra-y -carboxylato-rhodium(ii) complex (2) by nucleophiles L (pyridine, picolinic acid, niacin, or isonicotinic acid) have been determined using T-jump. The rate-determining step 

Longato, F. Morandini, and S. Bresadola, Inorg. Chim. Acta, 1978, 26, 157. 

Square-pyramidal metal carbonyls [M(CO)s] (M = Cr, Mo, or W) are generated on u.v. photolysis of metal hexacarbonyls and related compounds and appear as intermediates in photochemical replacement reactions of the six-co-ordinate species. The reaction step relevant in this context is an internal rearrangement of the square-pyramidal [M(CO)6] via a trigonal-bipyramidal intermediate, and back to the square-pyramidal ground state. This spy - tbp spy process represents an inverse Berry mechanism and also accounts for many other aspects of the photochemistry of these compounds.  

Intramolecular rearrangement in five-co-ordinate cobalt(i) and rhodium(i) complexes of the type [ML4((CN)2C—C(CN)2 ]+, where L represents various cyano-substituted organic ligands, are shown to be due to Berry pseudorotation, to rotation around the tetracyanoethylene double bond, and to catalysis by anions due to formation of ion pairs. 

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Brodbelt J, Liou C-C and Donovan T 1991 Selective adduct formation by dimethyl ether chemical ionization is a quadrupole ion trap mass spectrometer and a conventional ion source Ana/. Chem. 63 1205-9... 

The monomers are electron pair acceptors, and donor molecules are often able to split the dimeric halide molecules to form adducts thus, whilst the dimeric halides persist in solvents such as benzene, donor solvents such as pyridine and ether appear to contain monomers since adduct formation occurs. Aluminium halides, with the one exception of the fluoride, resemble the corresponding boron halides in that they are readily hydrolysed by water. 

In each case the configuration around the boron changes from trigonal planar to tetrahedral on adduct formation. Because of this ability to form additional compounds, boron trifluoride is an important catalyst and is used in many organic reactions, notably polymerisation, esterification, and Friedel-Crafts acylation and alkylations. 

Hartshorn and Thompson have also found evidence for adduct formation with o-xylene, n.m.r. investigations of the reaction solution revealing peaks in... 

Activated tertiary amines such as triethanolamine (TEA) and methyl diethanolamine (MDEA) have gained wide acceptance for CO2 removal. These materials require very low regeneration energy because of weak CO2 amine adduct formation, and do not form carbamates or other corrosive compounds (53). Hybrid CO2 removal systems, such as MDEA —sulfolane—water and DIPA—sulfolane—water, where DIPA is diisopropylamine, are aqueous alkaline solutions in a nonaqueous solvent, and are normally used in tandem with other systems for residual clean-up. Extensive data on the solubiUty of acid gases in amine solutions are available (55,56). 

The rather low values for the methylene groups of barbituric acid and its 2-thio derivative indicated a particularly easy adduct formation (84) which proceeds in water in excellent yield. 

The dimensionless acceptor number, AN, ranked the acidity of a solvent and was defined for an acidic solvent A as the relative P NMR downfield shift (A3) induced in triethyl phosphine when dissolved in pure A. A value of 0 was assigned to the shift produced by the neutral solvent hexane, and a value of 100 to the shift produced by SbClj. Gutmann suggested that the enthalpy of acid-base adduct formation be written as ... 

I 97. Efarris, C. C. (1989). Interindividual variation. among humans in carcinogen metabolism, DNA adduct formation and DNA repair. Carcinogenesis 10, 1563-1566. 

Drago and co-workers have correlated a large body of enthalpies of adduct formation in Lewis acid-base systems, including some solvents as reactants, with this four-parameter equation ... 

Cyclooctanone, condensation with diethyl carbonate, 47, 20 Cyclopentadiene, adduct formation with 1,2,3-benzothiadiazole 1,1-diox-ide, 47, 8... 

In addition to systems of the above type, i.e. involving adduct formation, various other types of synergistic extraction systems are recognised and have been reviewed.4 An example is the synergistic influence of zinc in the extraction and A AS determination of trace cadmium in water.5... 

Adduct formation by IrCl(CO)(PPh3)2 and similar compounds results in a shift in the IR carbonyl stretching frequency (Table 2.8). 

There is significant metal-metal bonding in the platinum compound, whose geometry involves a square of platinum atoms another important difference is that the coordination geometry is square planar in palladium acetate but octahedral in the platinum analogue. Different oligomers exist in solution, broken down by adduct formation. Palladium(II) acetate may be obtained as brown crystals from the following reaction [65] ... 

Cyclopentadienyl)gold is a very unstable, even explosive, yellow solid stabilized by adduct formation with tertiary phosphines. 

The key step in the radical chain decomposition of alkanesulfonyl halides as well as in the adduct formation of sulfonyl halides with alkenes (vide infra) is equation 8 in which the R radical abstracts an X atom from the sulfonyl halide to regenerate a sulfonyl radical. 

Attempts to isolate dimethylsulfoxide adducts failed, although spectral evidence suggests adduct formation in solution. Hoyer et al. 

PMc3 to give the complex salts 21 as shown in Scheme 12. Compounds of type 20 and 21 have successfully been tested for their catalytic efficiency. However, it was observed that fBuaPNSiMea failed to show similar adduct formation and this failure was attributed to steric crowding. 

Fig. 4. Changes of the structural parameters resulting from adduct formation...

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