NMR Spectroscopic Characterization

Fig. 6-4. Minimum energy conformations of L-PA and L-phenylalanine-A -methyl-anilide (L-PMA) based on molecular mechanics calculations and UV- and NMR-spectroscopic characterizations. (From Lepisto and Sellergren [25].)...

The X-ray structure of [cp Ir(CNR)Cl2], CNR = l,3,4,6-tetra-0-acetyl-2-deoxy-2-isocyano-Q,, 3-D-glucosc, has been determined.428 The synthesis of chiral complexes of Ir111 with Q-amino acid anions, L-L, of general formula [cp Ir(Cl)(L-L )] (252), and their NMR spectroscopic characterization, have been detailed. The X-ray structures of (252), L-L = L-proline and [cp Ir(Cl)(L-His-OH)]Cl, His = histidine, are described.429 C-allylglycinate binds in a terdentate manner in (253), which has been characterized by X-ray diffraction studies.430 C-vinylglycinate forms complex (254). 

Siehl, H.-U. Excursions into Long-Lived Vipyl Cations NMR Spectroscopic Characterization a-Aryl Vinyl Cations, In Stable Carbocation Chemistry Prakash, G.K.S. Schleyer, P. v. R., Eds. Wiley New York, 1997 Chapter 5, p. 165 - 196. 

The isolation and/or NMR spectroscopic characterization of cr-complexes, as that shown by 1, have received considerable attention over the past two decades, because of the relationship between the formation of such adducts and that of the metastable cyclohexadienyl intermediates postulated in the S Ar mechanism. The detailed structures of these adducts are now well known, and their reactions, the kinetics and thermodynamics of their formation and decomposition, as well as their spectral properties have been investigated in detail5,11,12. Although these studies constitute an important contribution to the understanding of the intermediates involved in Ar, they will not be discussed in this chapter since they have been recently reviewed furthermore, most of the cr-adducts were formed by the addition of anionic nucleophiles13,5,11. 

III. NMR SPECTROSCOPIC CHARACTERIZATION AND FLUXIONAL BEHAVIOR A. Conjugated 1,3-Diene Complexes... 

Many valuable reviews of the chemistry of these species are given in the new book Dicoordinated Carbocations An introduction by Grob " is followed by reviews of various theoretical studies of vinyl cations, their gas-phase chemistry, their generation by nuclear decay, and their NMR spectroscopic characterization. Vinyl cation production by addition to acetylenes and allenes, by solvolysis, and photolytically are covered, together with the chemistry of the species generated in these various ways. The next chapter deals with the synthetic applications of vinyl cations,and alkynyl and aryl cations are covered in the last chapter. A review of the NMR spectroscopic and quantum-chemical investigation of vinyl cations in superacid media (also of dienyl and 1-cyclopropylvinyl cations) is published separately,as is a review of alkynylcar-... 

The test oligosaccharide, GXS, was characterized extensively on a Bruker WH-400 NMR spectrometer (operating frequency 400 MHz) by 1D-and 2D-NMR spectrtoscopy. The synthesis (13) and the NMR spectroscopic characterization (13 14) of GXS has been reported elsewhere. 

Another type of adducts [8, Eq. (3)] was formed by the reaction of di(fert-butyl)aluminum chloride with dilithium bis(trimethylsilyl)hydrazide in low yields below 30% [19]. The structure of 8 consists of a distorted heterocubane with four vertices occupied by nitrogen atoms, two of which are connected by an intact N—N bond across one face of the cube. The cation positions are occupied by two aluminum and two lithium atoms, of which the last ones bridge the N—bond. Part of the hydrazide molecules was cleaved, and the aluminum atoms are bonded to one ferf-butyl group only. On the basis of the NMR spectroscopic characterization many unknown by-products were formed in the course of that reaction, and no information is available concerning the reaction mechanism. Compound 8 may be described as an adduct of dilithium bis(trimethylsilyl)hydrazide to a dimeric iminoalane containing a four-membered AI2N2 heterocycle. Further... 

The reaction of silole 44 with KH in THF or DME yields, after work-up with D2O, quantitatively the corresponding deuteriated silole (equation 52) metalated siloles have been suggested as intermediates80. In contrast, the analogous treatment of silole 45 with KH yields a mixture of three NMR spectroscopically characterized potassium compounds (equation 53). The main product of this reaction is the pentavalent silicate 46, which results from the nucleophilic attack of a hydride at the silicon center109. The other two products result from hydride addition to one of the ring carbons. 

The synthesis and detailed H, 13C, 77Se, and 125Te NMR spectroscopic characterization of the corresponding triflates have been reported by Laali et al 275 The 77 Se... 

In a very significant development, the parent 277-azepine 85 was prepared for the first time (Scheme 10) <1995AGE1469>. A ring construction was adopted involving A-BOC deprotection of 84 followed by treatment with strong base to afford 85 after intramolecular imine formation and base-induced elimination of acetate. While the yield was only 1%, the azepine was sufficiently stable at 25 °C for 48 h to allow for H and 13C NMR spectroscopic characterization. 

Singlet phenylnitrene thermally ring expands in the inner phase of a hemicarcerand to the cyclic ketenimine (54), whose polymerization is prevented by the surrounding host.104 This allowed the activation parameters for the ring contraction of (54) to be measured and for the NMR spectroscopic characterization of (53). 

Vanadium-Contaminated Aluminas and Aluminosilicate Gels 51V NMR Spectroscopic Characterization... 

Despagnet E, Gornitzka H, Rozhenko AB, Schoeller WW, Bourissou D, Bertrand G (2002) Stable non-push-pull phosphanylcarbenes NMR spectroscopic characterization of a methylcarbene. Angew Chem Int Ed Engl 41 2835-2837... 

Eyrisch, O, Sinerius, G, Fessner, W-D, Eacile enzymic de novo synthesis and NMR spectroscopic characterization of D-tagatose 1,6-bisphosphate, Carbohydr. Res., 238, 287-306, 1993. Henderson, I, Sharpless, KB, Wong, C-H, Synthesis of carbohydrates via tandem use of the osmium-catalyzed asymmetric dihydroxylation and enzyme-catalyzed aldol addition reactions, J. Am. Chem. Soc., 116, 558-561, 1994. 

D-Sorbitol 8 is a hexitol with its diol functions from C2 to C5 configured with the sequence threo, threo, erythro. The resulting Ci symmetry is possibly the reason for the rather small number of characterized complexes since the crystallization as well as the NMR spectroscopic characterization is hampered by the usually obtained mixture of species. 

In this section, NMR spectroscopic characterization of flexible regions in large proteins is discussed. As is apparent from this discussion, flexibility in such proteins encompasses a diversity of proteins of varying function. 

Comparing NMR spectroscopic characterization of proteins and small molecule... 

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