Solvent adduct

Analogous photoadditions have been observed on irradiation of pyrimidine and purine bases in ethers and amines. Irradiation of 1,3-dimethylur-acil (314) in tetrahydrofuran leads to the formation of 5- and 6-(tetrahydro-furan-2-yl)-5,6-dihydrouracils 315 and 316.261 Similarly, solvent adducts arising by way of initial hydrogen abstraction have been obtained on irradiation of pyrazine derivatives in diethyl ether or tetrahydrofuran.262 The... 

The determination of large values of the rate constant ratio ks/kpfrom the low yields of alkene product that forms by partitioning of carbocations in nucleophilic solvents. These rate constant ratios may then be combined with absolute rate constants for the overall decay of the carbocation to give absolute values of kp (s ).14 16 For example, the reaction of the l-(4-methylphenyl)ethyl carbocation in 50/50 (v/v) trifluoroethanol/water gives mainly the solvent adducts and a 0.07% yield of 4-methylstyrene from proton transfer to solvent, which corresponds to kjkp = 1400. This can be combined with ks = 6 x 109 s V4 to give kp = 4.2 x 106 s l (Table 1). 

The demonstration that formation of the nucleophile adduct R-Nu results in the same proportional decrease in the yields of the alkene and solvent adducts, so that the ratio of the yields of these reaction products is independent of [Nu-]. If the solvolysis and elimination reactions proceed by competing stepwise and concerted pathways, respectively, then the yield of R-OSolv will decrease with increasing trapping of the carbocation intermediate by added nucleophile, while the yield of alkene from elimination will remain constant, so that the ratio [R-OSolv]/[Alkene] will decrease as [Nu ] is increased. 

There are two lines of evidence that the reactions of simple tertiary derivatives such as [1]-C1 to give solvent adducts proceed through the corresponding tertiary carbocation intermediates (1) There is a large steric barrier to the... 

Values of the rate constant ratios ks/kp for partitioning of carbocations between nucleophilic addition of solvent and deprotonation. These rate constant ratios were determined by analysis of the yields of the solvent adduct and alkene that form by partitioning of the carbocation (equation ) ... 

The partitioning of simple tertiary carbocations, ring-substituted 1-phenylethyl carbocations, and cumyl carbocations between deprotonation and nucleophilic addition of solvent strongly favors formation of the solvent adduct. The more favorable partitioning of these carbocations to form the solvent adduct is due, in part, to the greater thermodynamic stability of the solvent... 

Direct interception of the initially formed bicyclic oxyallyl zwitterion derived from cyclohexadienones is difficult, due to its facile rearrangement to cyclopropyl ketone. One notable exception is the observation that 4-trichloromethyl-substituted dienone 94 gave solvent adduct 97 when irradiated in methanol, and both 97 and 98 upon irradiation in acidic methanol (Scheme 24)48. It was proposed that 97 arises either from a facile... 

The analogous 2,6-cycloheptadien-l-ones display zwitterion-derived reactivity as well52,53. For example, the parent compound 113, upon irradiation in either acetic acid or t-butanol, gave diastereomeric solvent adducts 114 and 115 (Scheme 28)52a. On the other hand, tetramethoxy derivatives 116 furnished rearranged products 117, which are equivalent to the cyclopropyl ketone 1,4-shift products seen with cyclohexadienones52b. 

It is generally accepted that photolysis of R3SnX (R = alkyl group X = halogen) results in the homolytic cleavage of the Sn—X bond. However, under certain conditions, for example in polar solvents such as EtOH which can act as a Lewis base, the photochemistry can switch to heterolytic cleavage of the Sn—X bond followed by formation of solvent adducts such as R3(X)Sn(Sol) (Sol = solvent)17. 

A az, s ) and solvent (k, s ) to a carbocation intermediate of solvolysis are first determined from the ratio of the yields the azide ion and solvent adducts (equation (1)). The value for may then be calculated from this product rate constant ratio M ), and az = 5 X 10 s for the diffusion limited... 

Protonated and cationized species are the most commonly detected ions using the ES process if a positive ionization mode is selected. Protonation is a result of the addition of proton(s) to a neutral molecule for every proton added, a net charge of +1 will result. Similarly, canonization is due to the addition of cation(s) to a neutral molecule. Detection of cationized ions can be useful in the determination of molecular mass of unknown analytes.If ESI is operated under negative ion mode, deprotonated ions will usually be the most dominant ions. Eor either operation mode, solvent adducts of the protonated/deprotonated ions are frequently detected in ESI/MS mass spectra. 

M. Fichtner, O. Fuhr, Synthesis and structures of magnesium alanate and two solvent adducts , J. Alloys Compd. 345 (2002) 286-296. 

A one-electron oxidation study of quercetin (see structure below) and quercetin derivatives (rutin) by DPBH, CAN, or dioxygen in protic and aprotic solvents has shown that quercetin radicals quickly disproportionate to generate quercetin and produce a quinone. This quinone adds water molecules and is then degraded. Oligomerization might be a minor route in media of low water content. Oxidation of quercetin-serum albumin complex retarded water to the quercetin quinone. The role of the quercetin 3-OH was established as follows (1) allows the formation of jo-quinonoid compounds, quickly converted into solvent adducts which still react with one-electron oxidants, and (2) in its deprotonated form stabilizes radicals, allowing autoxidation to proceed under mild conditions. 

Lepine, F., Milot, S., and Vincent, N. Formation of toxic PCB congeners and PCB-solvent adducts in a sunlight irradiated cyclohexane solution of Aroclor 1254, Bull. Environ. Contam. Toxicol, 48(1) 152-156, 1992. 

Bis-solvent adducts [Ni(cyclam)(solvent)2](C104)2 were also isolated in the solid state but in general they are unstable. 6... 

Rh(0H)3H20 (161, 236) and hexachlororhodate(III) have also been reported (19). The carboxylates are initially isolated as the solvent adduct, but heating under vacuum is adequate to prepare the anhydrous product. A variety of donors can occupy the terminal positions of the copper acetate type structure found in these rhodium dimers. No simple explanation of the bond order in these compounds seems adequate to describe the metal-metal attractive force in view of the number of electrons available and the prominent role of axial ligands in the total bonding scheme (200). 

Adducts of alkali metal salts prepared in anhydrous alcoholic media generally retain very little alcohol of solvation after being dried under vacuum at room temperature (see Table I). The unusual ability of adducts of D-glucitol to retain alcohol is probably due largely to the great ability of D-glucitol itself to retain solvent. Adducts of alkaline-earth metal salts, however, are more strongly solvated by alcohol than adducts of alkali metal salts. For example,21 lactose CaClj 4 MeOH is relatively stable at 60° at atmospheric pressure under vacuum (< 19 mm. of Hg), a molecule releases only two of the four molecules of methanol. From aqueous alcoholic media, adducts of alkaline-earth metal salts tend to crystallize as hydrates. 

When Complex 4 is dissolved in methanol the P-31 NMR spectrum of the resulting solution is a sharp doublet 8 = 17.1 ppm and Jp Rh = 153 Hz. Exposure of the solution to hydrogen leads to a quantitative change concomitant with hydrogenating the ligand. The new resonance at 8 = 43.0 ppm, and/P Rh 200 Hz is indicative of a solvent adduct 6 and no trace of the corresponding dihydride 7 is observed... 

Thuery, P., Nierlich, M., Bryan, J.C. et al. 1997. Crown ether conformations in 1,3-calix[4]arene bis(crown ether) Crystal structures of a cesium complex and solvent adducts and molecular dynamics simulations. J. Chem. Soc. Dalton Trans. 1997 (22) 4191 4202. 

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