Adduct anions

The neutral and anionic adducts of the halides constitute a large proportion of the complexes of Ti, and the alkoxides (also prepared from TiCU) are of commercial importance (p. 968). 

Is para-nitrofluorobenzene more or less susceptible to attack by methoxide than fluorobenzene Calculate the energetics of the reaction. (Energies for phenyl fluoride and para-nitrofluorobenzene methoxide anion adducts are available.)... 

Electrostatic potential map for para-nitrofluorobenzene methoxide anion adduct shows most negatively-charged regions (in red) and less negatively-charged regions (in blue). 

An analogous study concerned with the synthesis of prostaglandin analogs was also highly diastereoselective. The initial anionic adducts were quenched with various aldehydes, however, the diastereoselectivity at the carbinol stereocenter was not reported21. 

The radical anions of dialkyl sulfoxides (or sulfones) may be obtained by direct capture of electron during y-irradiation. It was shown that electron capture by several electron acceptors in the solid state gave anion adducts 27. It was concluded276 that these species are not properly described as radical anions but are genuine radicals which, formed in a solid state cavity, are unable to leave the site of the anions and exhibit a weak charge-transfer interaction which does not modify their conformation or reactivity appreciably, but only their ESR spectra. For hexadeuteriodimethyl sulfoxide in the solid state, electron capture gave this kind of adduct 278,28 (2H isotopic coupling 2.97 G is less than 3.58 G normally found for -CD3). 

Numbers used in this cycle AG° for hydroxide plus monomethyl sulfate, assumed to be the same as for dimethyl sulfate estimated above AG° for ionization of monomethyl sulfate AG° for tautomerization of the anionic adduct, based on pK values estimated by the method of Branch and Calvin AG° for ionization of the apically protonated adduct, based on a pK estimated by the method of Branch and Calvin.)... 

While trifluoro and other halosilanes function by increased electrophilicity at silicon, nucleophilic reactivity of allylic silanes can be enhanced by formation of anionic adducts (silicates). Reaction of allylic silanes with aldehydes and ketones can... 

A study of the reaction of chlorobenzene with /V-mclhyl aniline in the presence of Pd[P(r-Bu)3]2 and several different bases indicated that two mechanisms may occur concurrently, with their relative importance depending on the base, as indicated in the catalytic cycle below. The cycle on the right depicts oxidative addition followed by ligation by the deprotonated amine. The cycle on the left suggests that oxidative addition occurs on an anionic adduct of the catalyst and the base, followed by exchange with the amine ligand.167... 

Further substantive support for the participation of the Sn(ANRORC) mechanism can be taken from two important observations (1) and C NMR spectroscopy of solutions of 2-A-pyrimidines in liquid ammonia containing potassium amide firmly proves the presence of the anionic adduct 6-amino-l,6-dihydropyrimidinide (44) (74RTC325), the initial adduct in the ANRORC process and (2) the azadiene intermediate (41, which as mentioned above can be isolated) easily converts into 2-amino-4-phenylpyrim-idine on treatment with potassium amide in liquid ammonia. Both observa-... 

I. Additions. Radicals can react with anionic species to give radical anion adducts as shown for radical 11. Such addition reactions are steps in chain reaction processes described as SrnI (unimolecular radical nucleophilic substitution) reac-... 

The simplest modification occurs on addition of nucleophilic anions X to Lewis acids MX , resulting in the creation of an ate-complex as anionic adduct (Table 11) (reaction 162). The formation of complex anions can also be the result of halogen addition, with the formation of mixed or symmetrical trihalides [YX2], or else of hydracid addition, with formation of anions [XHY]-, which are not very stable and readily dissociated in solution but are characterizable in the solid state (reaction 163). 

The characterization of adduct 30 has also been made via C-NMR.90 The l3C chemical shifts of the anionic adduct 30 have been compared with those of the neutral adduct 33, formed from NH2 and l-methylpyrimidinium cation. Only a small difference (0.4 ppm) is found for the C-a atoms, reflecting a remarkable similarity of the sp3 carbons in the two adducts. 

Nitropyrimidine, its 2- and 4-methoxy, and 2,4- and 4,6-dimethoxy derivatives react with acetone in the presence of potassium hydroxide to yield the potassium salts of the anionic adducts 74 and 75, with structures elucidated by spectral ( H-NMR, IR, and UV-visible) methods. The nucleophilic attachment was found to occur only at CH positions, and when there was a choice between 2- and 4(6)-positions, the latter was preferred.125,126 An adduct of the kind corresponding to structure 75 was also obtained by using the conjugate base of acetophenone. The adducts can be converted to the corresponding CH3COCH2- or PhCOCH2-substituted pyrimidines by oxidation, either directly or via the related dihydropyrimidine derivatives.127... 

XVI), most of the aforementioned change does not appear to be caused by an electron density increase at C-5 but by the change to a dihydropyrimidine structure. This is conceivable if the adduct is not a free anion but is strongly associated with lithium. Further information about the structure of adduct 96 comes from a comparison between the anionic adduct 30 with the neutral adduct 33, formed from pyrimidine and 1-methylpyrimidinium cation, respectively, by reaction with NH2". Here the C-5 position of the anionic adduct is found to be 10.2 ppm upheld with respect to the neutral adduct. If it is assumed that in ammonia the anionic adduct is not associated with the positive counterion, the aforementioned phenyllithium adduct is more likely to possess a slightly delocalized electronic structure (104) resembling that of a dihydropyrimidine. This fact is not surprising, also in view of the low polarity of the solvent. 

The formation of anionic -adducts resulting from the primary attachment of neutral nucleophiles followed by proton elimination has been described only occasionally. A definite example is the reaction of methyl-amine with 2-nitrophenazine 10-oxide in DMF, leading to adduct 118.161 This structure is well supported by spectral evidence. It is characterized by two... 

Indirect evidence for the formation of anionic adducts has been obtained for some dehalogenation reactions of 5-haIouracils or 5-halo-5,6-dihydro-uracils with bisulfite ion in water.163"165 However, no adducts were detected in the course of these reactions. Similarly, the formation of adduct 120 was assumed in the reaction of 6-bromomethyl-l,3-dimethyl-5-nitrouracil with KCN to yield 6-cyano-l,3-dimethyl-5-nitrocyclothymine.166 Clearly, in all these reactions involving the uracil system, the ring charge delocalization is quite limited, and the resulting stability of the adducts is markedly reduced. 

Two of three nitrofluorobenzene isomers react with methoxide, but the third is unreactive. Obtain energies of methoxide anion (at left), ortho, meta and para-nitrofluorobenzene, and the corresponding ortho, meta and para-methoxide anion adducts (so-called Meisenheimer complexes). Calculate the energy of methoxide addition to each of the three substrates. Which substrate is probably unreactive What is the apparent directing effect of a nitro group Does a nitro group have the same effect on nucleophilic aromatic substitution that it has on electrophilic aromatic substitution (see Chapter 13, Problem 4) Examine the structures and electrostatic potential maps of the Meisenheimer complexes. Use resonance arguments to rationalize what you observe. 

Kona et al.217 reported DFT calculations on gas phase S V reactions such as Equations (57), (58), and other similar processes. Their calculations show the expected strong stabilization of the anionic adduct... 

Piperidine and morpholine react160 with benzylideneacetylacetone 85 to form a mixture of zwitterionic and anionic adducts (86 and 87, respectively) which forms benzaldehyde, acetylacetone and starting amine, as shown in Scheme 37. This has been confirmed by kinetic investigations in DMSO/water (50%). 

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