Etheral O-atom

The hydrolysis of diphenhydramine and analogues (11.24, Fig. 11.2) has been studied extensively [46 - 48], These compounds are essentially inert toward base-catalyzed hydrolysis, but do undergo proton-catalyzed hydrolysis, the mechanism of which is shown in Fig. 11.2. The reaction begins with protonation of the ether O-atom and continues with the irreversible heterolytic cleavage of the C-0 bond to produce the benzhydryl cation. This reaction is greatly facilitated by the weakening effect of the benzhydryl moiety on the adjacent C-0 bond. The benzhydryl cation itself is stabilized by resonance, which also explains why the reaction is facilitated. The last step is the for-... 

In cA-3,4a,5,7a-tetrahydro-6,7a-diphenylcyclopenta[l,2-e]-l,2,4-trioxin-5/ -yl hydroperoxide (24) (P2i/c, O - O = 2.87 A, 0- - -H=1.99A, O- - - H-O = 172°), hydrogen bonding occurs between the OOH proton and the ether O (Figure 15). On the basis of pXhb data alone, an association via the endoperoxide entity of the molecule would have been expected . The affinity for H-bond formation toward ether O atoms is documented in the number of cocrystaUization adducts between ether molecules and alkyl... 

Treatment of compound 222, containing a 1,2,4-trioxane ring fused to a cyclopentene ring, with O2 leads to formation of a hydroperoxide (223) with ene displacement, as shown in equation 76. The structure of 223 was determined by single-crystal XRD analysis. A contact of the hydroperoxy group with the endocyclic ether O atom of a neighboring molecule (287.4 pm) points to weak H-bonding. ... 

The crystal structure of the Gd3+ complex of ODOTRA (the analog of D03A with the macrocyclic NH replaced by an ether oxygen) [89], shows that the Gd3+ ion is 9-coordinate, bound to three amine N-atoms, one ether O-atom, four car-boxylate oxygens (one of which is bridging from a neighbor molecule in an infinite chain) and one water molecule with a twisted CSAP geometry. 

Polymerisation of w-butyl isocyanate was carried out with the Pruitt-Baggett adduct Re(OR)2Cl [267] at ambient temperature, yielding polyamide, a polymer of the nylon-1 type (Table 9.3) [268]. For more detailed mechanistic studies, -butyl isocyanate was also subjected to polymerisation with a catalyst derived from the reaction of the Pruitt-Baggett adduct with /i-naphthyl-/V-( -butyl) urethane (for the sake of clarity, the catalyst association and internal complexation of the Fe atom by etheral O atoms of the OR substituent are omitted in formulae) ... 

The aluminum-mediated Petasis-Ferrier rearrangement is a stepwise [1,3]-sigmatropic process. The first step is the coordination of the Lewis-acid to the 0-atom of the enol. Coordination to the ether O-atom is reversible and nonproductive. Cleavage of the adjacent C-O-bond, assisted by the antiperiplanar lone pair of the etheral O-atom, stereospecifically gives rise to an oxocarbenium enolate species, which cyclizes to the desired oxacycle. The rate difference in the rearrangement for the five- versus six-membered series can be explained by the more facile 6-(enolendo)-endo-trig cyclization. The last step is the intramolecular equatorial hydride delivery. 

Figure 1. Chemical structures of the dianions of 9-[2--(phosphonomethoxy)ethyl]adenine (= PMEA Adefovir) [1] and of 9 [2--(phosphonomethoxy)ethyl]-8 azaadenine (= 9>8aPMEA )> together with the structure of PME-R, whereR is a non-interacting residue, and which represents the metal ion-coordinating properties of the ether-phosphonate chain occurring in PMEA and 9>8aPMEA. A further ligand to be considered in this study is 9-(4-phosphonobutyl)adenine, which is abbreviated as dPMEA2-(=3-deoxa-PMEA-)to indicate that its structure corresponds to that of PMEA except that the ether O atom is replaced by a CH group.

Phenyl and benzyl acetates both show the loss of ketene via H-transfer to an ether O atom ... 

The effects on the conformations of complexes of Sb(III) and Bi(III) of the rigid maleonitrile units present in four related mixed thia-oxa macrocycles and of the ligands themselves has been investigated by variable temperature solution and C H NMR studies together with molecular modeling. The Sb and Bi complexes were thought to show a preference for coordination via the ether-O atoms. " ... 

The fact that the 2 OH groups may form H-bonds with the ether O atoms of neighboring ribose residues is highly important, since the different behavior of RNA and DNA - as far as this difference is due to the 2 OH groups - is caused by the structure promoting effect of such hydrogen bonds. Consequently, the rod-like structures formed by RNA in neutral medium are stabilized by these H-bonds. 

Figure 8 shows IR spectra of t RNA dependent on temperature (for details see Reference 2). As with DNA, the base pairing is indicated by the splitting of the C=0 stretching vibrations in the (G-hC) pairs. This splitting vanishes with increasing temperature (Figure 8a). The 2 OD groups form hydrogen bonds with the ether O atom of the neighboring ribose residues. This is shown in Figure 8b At 55 °C, when...

Consequently, the Mg ion-induced structure change observed by Schulte, Morrison, and Garrett [34] is probably as follows Firstly, the double helical regions become more compact. Secondly, the Mg " " ions induce strong H-bonds in the backbone between the 2 OD groups and the ether O atoms of the neighboring ribose residues. 

Different types of van der Waals interactions are observed in the complexes. Hydrogen bonds formed between the ammonium Hn atoms and the crown ether O atoms. The strongest Hj jO bonds in complexes of dibenzo-18-crown-6 ether with ammonium cation have a CE of 0.9 eV per bond [7] and bond distances of 1.8 A. The H atoms of the methylene and/or the phenyl group interact with the O atoms of ethers. The weakest interactions observed are between H atoms and phenyl groups as well as between two phenyl groups. In addition, the interactions are not always 1... 

This means, there is an open species in which M is only phosphonate-coordinated, M(PMEA)op, and which then interacts either with N7 or the ether O atom giving the chelated isomers, M(PMEA)ci/n7 or M(PMEA)d/o, respectively. 

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