Intermolecular 1,3-hydrogen shift

The crossover product, propionaldehyde-l,3-d-3- C 12, clearly demonstrated that the isomerization occurred via intermolecular 1,3-hydrogen shift. These results are consistent with a modified metal hydride addition-elimination mechanism which involves exclusive 1,3-hydrogen shift through oxygen-directed Markovnikov addition of the metal hydride to the carbon-carbon double bond (Scheme 12.2). The directing effect of functional groups on the selectivity of transition metal catalysis is well presented [9], and an analogous process appears to be operative in the isomerization of allylamines to enamines [10]. 

A solution-state and solid-state nuclear magnetic resonance study of the complex and its separate components in both their neutral and ionized (TMP hydrochloride and SMZ sodium salt) forms was undertaken in order to elucidate the TMP-SMZ interactions. Inspection of the data for the complex in the solid state shows that the 13C chemical shifts are consistent with the ionic structure proposed by Nakai and coworkers105 (14). Stabilization of the complex is achieved by the resulting ionic interaction and by the formation of two intermolecular hydrogen bonds. 

The O—H N hydrogen bond in the phenylazoresorcinol monoanion is strong, giving a large and positive value of A[S( H) — 8( H)], characteristic of a double minimum potential (Hibbert and Phillips, 1989). Two examples of intermolecularly hydrogen-bonded species for which the isotope effect on the chemical shift has been measured are also given in Table 5. 

Waals radii of two atoms (2.90 A). Nevertheless, each reaction site is far apart the hydrogen abstraction from the benzyl group proceeds and the product was obtained in optically active form. In this case, another mechanism besides the direct intramolecular hydrogen abstraction from the benzyl group may be involved, like intermolecular hydrogen abstraction or hydrogen shift. 

The situation becomes more complicated in CH2CI2 solutions. For example, the v(OH) regions in the IR spectra, recorded for 1 1 mixtures of ReH2(CO)(NO) (PR3)2 and (CF3)3COH, show the red frequency v(OH) shifts of 243 to 370 cm . It is obvious that the proton donor participates in intermolecular hydrogen... 

Oximes show strong intermolecular hydrogen bonding, in nonpolar solvents, which affects the H NMR chemical shifts and coupling constants. The influence of this interaction on the conformational equilibrium and on some selected coupling constants 7cf and Jcp) was evaluated. Thus the H and C NMR spectra in different solvents were obtained. Both 7hf and Jcf are sensitive to the F—C—C=N orientation (Tables 18 and 19). 

In polypeptide blends, the balance of intra- and intermolecular hydrogen bond interactions in two kinds of polypeptide chains play an important role for the conformational stability and the blend miscibility. The observation of the 13 C NMR chemical shifts and relaxation times, and the two-dimensional... 

In the acid-catalyzed isomerization of straight-chain alkanes to higher-octane branched ones, after initial protolytic ionization, alkyl and hydrogen shifts in the formed carbocations lead to the most branched and therefore thermodynamically preferred, generally tertiary, carbocations. Intermolecular hydrogen transfer from excess alkane then produces the isomeric isoalkane with the formed new carboca-tion reentering the reaction cycle. 

Observed chemical shifts are affected by intermolecular interactions. Ideally 8, should be determined in the gas phase at low pressure, but this is generally impractical to do. The next best approach is to use a dilute solution of the compound in an inert solvent. For organic compounds, the most widely used solvents are CDC13 and CC14. For alcohols, the OH proton shift varies very considerably with concentration of the solution, as a result of intermolecular hydrogen bonding. 

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