Experimental Structural Studies

Hiller and coworkers reported an NMR and LC-MS study on the structure and stability of l-iodosyl-4-methoxybenzene and 1-iodosyl-4-nitrobenzene in methanol solution [195]. Interestingly, LC-MS analyzes provided evidence that unlike the parent iodosylbenzene, which has a polymeric structure (Section 2.1.4), the 4-substituted iodosylarenes exist in the monomeric form. Both iodosylarenes are soluble in methanol and provide acceptable and NMR spectra however, gradual oxidation of the solvent was observed after several hours. Unlike iodosylbenzene, the two compounds did not react with methanol to give the dimethoxy derivative ArI(OMe)2 [195]. 

Silva and Lopes analyzed solutions of iodobenzene dicarboxylates in acetonitrile, acetic acid, aqueous methanol and anhydrous methanol by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/MS) [196]. The major species found in the solutions of PhI(OAc)2 in acetonitrile, acetic acid and aqueous methanol were [PhI(OAc)2Na]+, [PhI(OAc)2K]+, [Phl]+, [PhIOAc]+, [PhIOH]+, [PhI02Ac]+, [PhI02H]+ and the dimer [Ph2l202Ac]+. On the other hand, the anhydrous methanol solutions showed [PhIOMe]+ as the most abundant species. In contrast to the data obtained for PhI(OAc)2, the ESI-MS spectral data of PhI(02CCF3)2 in acetonitrile suggests that the main species in solutions is iodosylbenzene [196]. A similar ESI-MS and ESI-MS/MS study of solutions of [hydroxy(tosyloxy)iodo]benzene has been performed under different conditions and, based on these data, mechanisms were proposed for the disproportionation of the iodine(III) compounds into iodine(V) and iodine(I) species [197]. 

Richter, Koser and coworkers investigated the nature of species present in aqueous solutions of phenylio-dine(III) organosulfonates [198]. It was shown by spectroscopic measurements and potentiometric titrations that PhI(OH)OTs and PhI(OH)OMs upon dissolution in water undergo complete ionization to give the hydroxy(phenyl)iodonium ion (Phl+OH in hydrated form) and the corresponding sulfonate ions. The 

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Variations in local geometries of organic compounds are often subtle and below the resolution of most experimental structural techniques. Thus, the full extent of structural variability was at first not so much apparent from experimental structural studies, but from ab initio gradient optimized geometries (Schafer 1982G, 1983G). 

No pyrido[l,2-6][l,2]thiazine derivative has been the subject of theoretical or experimental structural studies. 

The extremely sterically hindered 1,2,4-diazaphospholes 139-142 were prepared via [2+3] cycloaddition reaction of 2-(2,4,6-tri-/,< +-butylphenyl)-l-phosphaethyne 138 with trimethylsilyldiazomethane derivatives (Scheme 11). Structures of 1,2,4-diazaphospholes 140 and 142 were investigated by NMR spectroscopy and X-ray diffraction. The experimental structural studies as well as theoretical calculations confirmed aromatic character of these 1,2,4-diazaphospholes. The crystal structure of compounds 140 and 142 showed remarkable hydrogen bonding character in relation to molecular aggregation due to the presence of the bulky aryl groups <2007EJI3491>. 

Four main low-energy conformational families of eight-membered ring systems, consisting of the boat-chair, crown, boat, and chair forms, were surveyed in CHEC-II(1996). They are discussed in the foregoing sections of this chapter in conjunction with the theoretical and experimental structural studies of triheterocines (see sections 14.08.2 and 14.08.3). 

The many efforts to determine the structure of polymeric sulfur allotropes have been critically reviewed by Donohue in 1974 [8]. Since that time, only a few experimental results have been reported which, however, did not introduce new structural details. Most of the more recent studies on polymeric sulfur are focused on the unique polymerization transition in the liquid. Experimental structure studies Aerefore often deal with quenched sulfur melts (see for example [118, 119] and literature cited therein). On the other hand, the polymerization mechanism has attracted increased interest for theoretical studies (see for example [120-123] as well as the literature cited therein). 

A molecular-mechanics scan of the potential-energy surface of [M(L )]"+ indicates that the two distortional isomers (M-N7oM-N3) are nearly degenerate for cobalt(II) (see Figure 18-5) this effect emerges also from experimental structural studies [25]. The lower-energy, nearly flat curve in Figure 18-5 indicates that the... 

Poly(alkyl/aryloxothiazenes) are high-molecular-weight polymers and have good solubility properties. Their glass transition temperatures are quite high. For example, while [N=S(0)Me] has a Tg of 55-65 °C, [N=S(0)Ph]n has a Tg of 85 °C. Although experimental structural studies have been limited, based on theoretical calculations, a cis-trans helical conformation has been proposed for poly(methyloxothiazene), [N=S(0)Me] [29]. 

GFP-like proteins, KillerRed is a dimeric FP derived from chromoprotein anm2CP. Its photosensitizing ability has been extensively studied in eell cultures and other biological systems and confirmed to be related to ROS produetion. The main ROS produced is however not but the superoxide radieal anion (02 ) and hydrogen peroxide (H2O2), formed via Type I (eleetron transfer mediated) processes. Both theoretieal and experimental structural studies have been condueted in attempts to rationalise and improve the photosensitisation ability of KillerRed, however with limited success so far. ... 

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