Bond terminal

The mechanism of oxidation probably involves in most cases the initial formation of a glycol (15-35) or cyclic ester,and then further oxidation as in 19-7. In line with the electrophilic attack on the alkene, triple-bonds are more resistant to oxidation than double bonds. Terminal triple-bond compounds can be cleaved to carboxylic acids (RC=CHRCOOH) with thallium(III) nitrate or with [bis(trifluoroacetoxy)iodo]pentafluorobenzene, that is, C6F5l(OCOCF3)2, among other reagents. 

Thus there are five bonding electrons giving a bond order of 2.5, consistent with the bond length of 115 pm, versus 121 pm for the four-electron bond in O2 and 110 pm for the six-electron bond in N2. For these and other related molecules, the double-quartet model is a convenient and useful alternative to the conventional molecular orbital model. Moreover, it shows that for a singly bonded terminal atom such as F or Cl there is a ring of six nonbonding electrons rather than three separate lone pairs. As we will see in Chapters 7 and 8, this conclusion is confirmed by the analysis of electron density distributions. 

The dodecahydrododecaborate anion, B H 2-, is termed unique with considerable justification. This ion and its perhalo derivatives, e.g., Bi2C1i22-, are the most symmetrical molecular aggregates known. The boron atoms occupy the vertices of a regular icosahedron and each is bonded terminally to a hydrogen atom all boron atoms are environmentally equivalent.7,8 This anion is the only known example of the 7 symmetry group.8 General spectral, physical, and chemical properties of Bx2Hi22-are detailed in a paper by Muetterties et al.9... 

In the course of degradation of nonesterified and low-esterified substrates by pectate lyases, the glycosidic bonds can be split either at random or terminally, starting from the reducing end of the molecule. On the other hand, in the course of splitting of highly esterified substrates by pectin lyases, only the random-action pattern is operative. So far, no pectin lyase is known that can split the glycosidic bonds terminally. 

Reactions in which two o bonds terminate at a single atom or made or broken in a concerted chemical reaction are called cheletropic reactions ... 

Table 9. Parameters characterizing the hydrogen-bond patterns in liquid water at 10 °C, and mass density lg/cm3. The mean number of hydrogen bonds terminating at a molecule is (b y no is the fraction of unbonded molecules, and n is the fraction with precisely one bond. Cj stands for the number of non-short-circuited polygons, per molecule of the liquid, with j sides...

The existence of a multiply bonded terminal Pd —O unit is further confirmed by ONMR spectroscopy. Previous studies revealed that... 

Draw the constituent orbitals for each component. These are p orbitals at each end of the n system and (usually) sp3 hybrid orbitals at each end of components (if the bond terminates at H, the orbital there is an s orbital). Disregard orbital... 

C-l-O-1 bond is long, 144.2 pm, as a consequence of being part of a chain of four C-O bonds terminating in a C=0 bond. 

Cheletropic reactions are cyclizations - or the reverse fragmentations - of conjugated systems in which the two newly made o bonds terminate on the same atom. However, a cheletropic reaction is neither a cycloaddition nor a cycloreversion. The reason is that the chelating atom uses two AOs whereas in cycloadditions, each atom uses one and only one AO. Therefore, Dewar-Zimmerman rules cannot apply to cheletropic reactions. Selection rules must be derived using either FO theory or correlation diagrams 38 The conjugated fragment39 of 4n + 2 electron systems reacts in a disrotarory (conrotarory) mode in linear (nonlinear) reactions. In 4n electron systems, it reacts in a disrotarory (conrotarory) mode in nonlinear (linear) reactions. 

Here, n is the number of singly bonded (terminal) atoms. 

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