NMR spectroscopic studies

The computational results (93JA2465) are consistent with the experimental findings of NMR spectroscopic studies (82JOC5132 97MRC35), which showed the presence of only the H tautomer of tetrazole in DMSO-dfi e = 49) solution. The content of H tautomer 27a in dioxane e = 22) at 30°C was estimated as 78% (82JST283) and 85% (75BSF1675) from its dipole moment 4.88 D and those of 1,5- and 2,5-dimethyltetrazoles as models for the H and 2H tautomers respectively. 

Based on IR and NMR-spectroscopic studies [76AHC(S1), pp. 406, 414 94MI1027 96CHEC-II(4)267], 2-mercapto-l,3,4-oxadiazole prefers the thione form 195. 

Evidence in favor of the amino-thionic tautomeric form of 2-amino-l,3,4-thiazoline-5-thione 239 (A = X = S R = H) was obtained from X-ray structural determinations [72AX(B)1584]. A NMR-spectroscopic study (77JOC3725) of compounds 239 (A = Se X = S R = Me) demonstrated their amino-thionic structure. A similar tautomeric form 240 is also dominant for the hydrazine derivative (R = NHNHCOPh) [73JCS(P2)4]. 

Likewise, temperature dependent H NMR spectroscopic studies on yV-phenyl-3//-azepin-2-amine indicate that one of the C3 protons is highly shielded, the other strongly deshielded.82... 

The selectivity for (/ ,/ )( ,S)-10 has been rationalized by invoking a synperiplanar enolate species whose conformation is enforced by a donor(enolate oxygen)- acceptor) peril uo-rophenyl) interaction depicted in structure N47. Infrared and variable temperature NMR spectroscopic studies of the neutral precursor complex 8 support the existence of such a donor-acceptor interaction. 

Variable-temperature H and 13C NMR spectroscopic study of this seemingly crowded molecule 38 revealed that the ring rotation about the iron ring axis occurs freely down to — 95 °C, although at lower temperatures the rotation of the... 

A variable-temperature NMR spectroscopic study of the titanium(IV) complex 43 also indicated free rotation of the five-membered rings, but, as in the ferrocene derivative 38 allowed the determination of the activation barrier for the phenyl ring rotation (AG (-90 °C) = 9.8 0.5 kcal mol1). 

More recently, Grubbs et al. obtained a refined mechanistic picture of the initiating step by conducting a 31P NMR spectroscopic study of the phosphine exchange in precatalysts 12-A. These investigations revealed that substitution of the phosphine proceeds via a dissociative-associative mechanism, i.e., a 14-electron species 12-B is involved that coordinates the alkene to give a 16-electron species 12-C (Scheme 12) [26a]. Increased initiation rates are observed if the substituents R and the phosphine ligands PR3 in precatalysts... 

Amides are derivatives of carboxylic acids, so that their coordination behavior to boranes might be similar to that of their parent compounds. B-NMR spectroscopic studies have shown that compounds 31 and 32 are monomeric species in solution, while compounds 33 and 34 with the more Lewis acidic 9-borabicyclo[3.3.1]nonyl unit form aggregates that may be dimeric, oligomeric, or polymeric. The grade of association could not be determined by mass spectrometric analyses, because in all cases only the monomer is liberated into the gas phase [65]. 

A systematic NMR spectroscopic study of these adducts suggests that the steric repulsion between the trimethyl aluminum Lewis acid and the phosphane Lewis base rather than the electronic factors account for the detected changes in the P-NMR spectroscopic chemical shifts (Table 1). The change in the chemical shift (A) of the phosphanes on coordination to AlMe3 has been correlated to the... 

Consequently, due to preferred cis-cis orientation a dimeric structure is observed for the indium complex and an unprecedented cis-trans arrangement in the thallium structure leads to a polymeric aggregate. Further N-NMR spectroscopic studies show that the aluminum and gallium complexes are stable contact ion pairs even in solution whereas the indium and thallium compounds are solvent-separated ion pairs in THE solution. 

NMR spectroscopic studies of the titanium tetraisopropoxide-HOCSAC mixture seemed to prove that the bimetallic species was formed and was very... 

NMR spectroscopic studies f111,13C, and 31P) are consistent with the dipolar ylide structure and suggest only a minor contribution from the ylene structure.234 Theoretical calculations support this view.235 The phosphonium ylides react with carbonyl compounds to give olefins and the phosphine oxide. 

P-NMR spectroscopic studies on the reaction course of the dinucleotide synthesis from 3 -0-acetylthymidine 5 -phosphate (pT-Ac) (180a) and 5 -0-trityl-thymidine (Tr-T) in the presence of triisopropylbenzenesulfonyl chloride (TPS) confirm the metaphosphate hypothesis 123,124). Successive addition of 0.5 equiv. 

The reaction of 2equiv. of a pyrrole-substituted cyclopentadiene with Zn[N(SiMe3)2]2 (Scheme 19) afforded the dicyclopentadienylzinc complex 23.52 A solid-state structure of this compound was not obtained, but room-temperature 1H NMR spectroscopic studies showed two equivalent cyclopentadienyl groups, whose signals broadened on cooling. 

The mono- and di-chalcogenides of dppm contain an acidic methylene carbon which can undergo deprotonation. NMR spectroscopic studies on the relative acidities of these methylene groups show an increase in acidity for the series R2PCH2PR2 < R2P(0)CH2P(0)R2 < R2P(S)CH2P(S)R2 <... 

NMR-spectroscopic studies and a single crystal X-ray structure determination of the reduced Co / form of 100 revealed the presence of a bridging 2,3-dibromo-3-phenyl-propionato ligand (threo dl pair). The complex bearing the erythro form of 2,3-dibromo-3-phenyl-propionate is only produced in minor yields <3%. Therefore, the bromination of the encapsulated alkene is a highly diastereoselective syu-addition. This is rather... 

C-NMR spectroscopic studies on a-substituted tris(ethynyl)methyl cations 49 prepared from alcohols 50 (equation 18) provided evidence for the participation of resonance structures with allenyl cationic character38. The parent tris(ethenyl)methyl cation (49, R = H) cannot be generated under stable carbocation conditions (SbFs/FSOsH) presumably due to the highly reactive unsubstituted termini of the three ethynyl groups and the resulting low kinetic stability. The chemical shift data (Table 1) give evidence that in all cases Ca and CY are deshielded more than Cg (relative to their precursor alcohols). 

Altoff, W., Fild, M., Rieck, H.-R, and Schmutzler, R., Synthesis and NMR spectroscopic studies of phosphorus compounds with vinyl and ethynyl groups, Chem. Ber., Ill, 1845, 1978. 

Hayashi et al. proposed a catalytic cycle for the rhodium-catalyzed 1,4-addition of phenylboronic acid to 2-cyclo-hexenone (Scheme 28), which was confirmed by NMR spectroscopic studies.96 The reaction presumably involved three intermediates, phenylrhodium a, oxa-7r-allylrhodium b, and hydroxorhodium c complexes. Complex a reacted with 2-cyclohexenone to give b by insertion of the carbon-carbon double bond of enone into the phenyl-rhodium bond followed by isomerization into the thermodynamically more stable complex. Complex b was converted to c upon addition of water, liberating the phenylation product. Transmetallation of the phenyl group from phenylboronic acid to rhodium took place in the presence of triphenylphosphine to regenerate a. 

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