O„ groups

The trivial name acetoxy is retained for the CH3—CO—O— group. Compounds of the type R C(0R )3 are named as R esters of the hypothetical ortho acids. For example, CH3C(OCH3)3 is trimethyl orthoacetate. 

Sultones and Sultams. Compounds containing the group —SOj—O— as part of the ring are called -sultone. The —SOj— group has priority over the —O— group for lowest-numbered locant. 

Reactions. The CF O— group exerts predominant para orientation in electrophilic substitution reactions such as nitration, halogenation, acylation, and alkylation (350). 

Several classes of polymers containing the HFIP-O group have been reported. These polymers show promise as film formers, gas separation membranes, coatings, seals, and other high temperature apphcations due to the properties imparted by this function, similar in many ways to the HFIP group. 

Synthesis and Properties. Several polymers containing HFIP-O groups have been investigated, the most common beeing epoxies and polyurethanes. The development of fluorinated epoxy resins and the basic understanding of their chemistry has been reviewed (127). 

Diphosphate tungsten bronzes (DTB) Cs Hg (P 04)4(W03)gai e chai ge-density wave (CDW) conductors. The framework of Cs contains columns of corner-sharing WO octahedra internked through P O group. Properties of Cs can be tuned via out-of-... 

Ramachandran plot (see Figure 1.7a). The a helix has 3.6 residues per turn with hydrogen bonds between C =0 of residue n and NH of residue n + 4 (Figure 2.2). Thus all NH and C O groups are joined with hydrogen bonds except the first NH groups and the last C O groups at the ends of the a helix. As a consequence, the ends of a helices are polar and are almost always at the surface of protein molecules. 

The CH connectivities can be read off from the CH COSY plot thus the complete pattern B of all //atoms of the molecule is established. At the same time an O//group can be identified by the fact that there is no correlation for the broad signal at <5// = 4.45 in the CH COSY plot. 

All the approaches for deblocking protective groups described earlier in this book have found application in the removal of protective groups from phosphorus derivatives. Because phosphate protection and deprotection are commonly associated with compounds that contain acid-sensitive sites (e.g., glycosidic linkages and DMTr-O- groups of nucleotides), the most widely used protective groups on phosphorus are those that are deblocked by base. 

By contrast, dissolution of OSO4 in cold aqueous KOH produces deep-red crystals of K2[0s 04(0H)2] ( perosmate ), which is easily reduced to the purple osmate , K2[0s 02-(0H)4]. The anions in both cases are octahedral with, respectively, trans OH and trans O groups. 

On the other hand, the catalytic effect of water as a base is stronger at the 2-position. This result can be explained if one assumes that the proton is transferred by a water molecule which solvates the O- group in the reagent 3-sulfo-l-naphth-oxide dianion. As can be seen in 12.148, the base is already in the optimum position when the stage of the o-complex is reached. This explanation is supported by a comparison of the entropies of activation for reaction at the 2- and 4-positions. 

In the case of the (CD3)2SOv radical anion it is expected that a larger part of the spin will be on the O-group (see Figure 1). 

FIGURE 1. Structures for Me2SCT(I) and MeSO" Me(II). The assignment of 0.5 spin density to each of the two axial ligands in I is only applicable to equivalent ligands in the Rundle formulation. Qualitatively, more spin density is expected to reside on the axial methyl than on the O group. Reproduced by permission of the authors from Reference 8. 

Show how resonance can occur in the following organic ions (a) acetate ion, CH,CO, (b) enolate ion, CH,COCH5, which has one resonance structure with a C=C double bond and an —O group on the central carbon atom (c) allyl cation, CH,CHCH,+ (d) amidate ion, CH,CONH (the O and the N atoms are both bonded to the second C atom). 

Because carbon stands at the head of its group, we expect it to differ from the other members of the group. In fact, the differences between the element at the head of the group and the other elements are more pronounced in Group 14/IV than anywhere else in the periodic table. Some of the differences between carbon and silicon stem from the smaller atomic radius of carbon, which explains the wide occurrence of C=C and G=Q double bonds relative to the rarity of Si=Si and Si=0 double bonds. Silicon atoms are too large for the side-by-side overlap of p-orbitals necessary for -it-bonds to form between them. Carbon dioxide, which consists of discrete 0=C=0 molecules, is a gas that we exhale. Silicon dioxide (silica), which consists of networks of —O—Si- O - groups, is a mineral that we stand on. 

As shown, an asymmetric carboxylic-sulfonic acid anhydride is formed, but the cellulose attack occurs on the C = O group, since a nucleophilic attack on sulfur is slow, and the tosylate moiety is a much better leaving group than the carboxylate group [193]. Similar to other acylation reactions, there is a large preference for tosylation at the 5 position, and cellulose tosylates... 

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