Triple bonds, formulation

In the cationic complex [(d75-C5H5)(CO)2Mn=CMe]+ the lack of symmetry in the metal fragment means that the two 7r-bonds are not degenerate. The percentage electron density of the two 7r-orbitals on the carbyne carbon have been calculated as 33 and 35%—relatively large figures which clearly support the triple bond formulation (28). 

The triple bond formulation did not receive theoretical support, however, as in 1978 Norman and Kolari presented their SCF-X"-SW calculations on [Rh2(02CH)4] and [Rh2(02CH)4(H20)2]. " Their calculations indicate that the non-bonding 5s and 5p, Rh-centered orbitals, important in Cotton s analysis, are at high energy and remain unoccupied. Their 14-electron core is a, 5, n, ... 

Apparently only one hetaryne containing oxygen as a hetero atom, 2,3-dehydrocoumarone (98), has been described thus far. It was formulated by Stoermer and Kahlert as an intermediate containing a triple bond in its hetero ring system as eaHy as 1902 and was probably the first aryne mentioned in the hterature of organic... 

The deoxyuric acids were early formulated with a cyclic triple bond (138) but recent chemical e ddcnce and ultraviolet spectral data have led to their reformulation as 139 or 140. Although the results of the early investigations of the structure of uric acid using chemical methods were interpreted in favor of structure 141i5s-i6g structure was considered to be supported by its ultraviolet spec-... 

Treatment with alkaline H2O2 oxidizes trialkylboranes to esters of boric acid. This reaction does not affect double or triple bonds, aldehydes, ketones, halides, or nitriles. The R group does not rearrange, and this reaction is a step in the hydro-boration method of converting alkenes to alcohols (15-16). The mechanism has been formulated as involving a rearrangement from boron to oxygenr ... 

The multiple bond to the metal in a rhenium(V) compound is best represented by the MO description of it being a triple bond, consistent with the symmetry of the px and p orbitals on the ligand see 1 (1). In keeping with that, these bonds are found to be relatively short and quite strong. The structure has also been presented as 1 a valence bond formulation that facilitates the counting of oxidation states but does not provide an accurate representation. 

The analogous reaction of 3 with W2(OrBu)6 gave a brown solution, from which a yellow, microcrystalline material could be isolated. Based on spectroscopic data the latter was formulated as [Cy7Si70i2]2W2(p-H)(0tBu) (158). Cleavage of the Mo = Mo triple bond in 157 occurred upon treatment of this compound with NO (two equivalents) to afford the dimeric nitrosyl molybdenum silsesquioxane complex [Cy7Si70i2]2Mo2(NO)2 (159). °°... 

The addition of ammonia or primary and secondary amines to acetylenes is greatly enhanced if electron-attracting groups are attached to or conjugated with the triple bond. This reaction may be formulated as in Eq. (31). 

Due to its ability to form inverted hexagonal phase, DOPE is believed to impart fusogenicity to lipoplexes, thus facilitating fusion followed by destabilization of the endosomal membrane, lipoplex escape from the endosomes, and eventually the DNA release. Indeed, inclusion of DOPE into lipoplexes was shown to enhance considerably the transfection activity of some of the cationic lipid carriers [35,120, 121]. For example, formulations of oxypropyl quaternary ammonium cationic lipids with 50 mol% DOPE have been reported to exhibit 2-5 times higher transfection activity in COS7 cells than formulations with pure cationic lipid (Fig. 29) [35]. Recently, a triple-bond dialkynoyl analog of DOPE has been... 

The bond order in a diatomic molecule is defined as one-half the difference between the number of electrons in bonding orbitals and the number of antibonding orbitals. The factor one-half preserves the concept of the electron pair and makes the bond order correspond to the multiplicity in the valence-bond formulation one for a single bond, two for a double bond, and three for a triple bond. Fractional bond orders are allowed, but are not within the scope of this discussion. 

Alkynyl substituents stabilize a radical center by the same 12 kcal/mol that on average is achieved by alkenyl and aryl substituents. From the point of view of the VB model this is due to the fact that propargyl radicals exhibit the same type of resonance stabilization as formulated for allyl and benzyl radicals in the right column of Table 1.1. In the MO model, the stability of propargyl radicals rests on the overlap between the one correctly oriented n system of the C=C triple bond and the 2 pz AO of the radical center, just as outlined for allyl and benzyl radicals in Figure 1.5 (the other 7t system of the C=C triple bond is orthogonal to the 2pz AO of the radical center, thus excluding an overlap that is associated with stabilization). 

Because structures 11-13 do not involve C-N triple bonds, Eq.(ll) shows that in Eq.(9), the Px(C)-px(N) and py(C)-py(N) spin-pairings form fractional 7ix(CN) and Jty(CN) electron-pair n-bonds via Heitler-London AO formulations of the bond wavefunctions. 

The conjugation of a double bond with a carbonyl group, C O, such as in an aldehyde, can have the serious adverse effect of greatly increasing the likelihood of the material being a severe skin irritant or sensitizer. Examples of this type of influence occur in citral, cinnamic aldehyde, and trans-2 hexenal, as well as in methyl heptine carbonate which has a conjugated triple bond. Benzylidene acetone, which is closely related in structure to cinnamic aldehyde, can no longer be used as a perfumery material for this reason, and the level at which other potential sensitizers can be used in perfume formulations is restricted (see pp. 183-185). 

Consideration of the degree of metal substitution at the carbons of the C2 fragment and the separations of the two carbon atoms, has led to the formulation of polymetallic species as permetallated ethyne (E), ethene (F), or ethane (G) (Chart 2).35 Addition of metal fragments to the unsaturated species E leads to sequential formation of F and G and progressive saturation of the C=C triple bond. These ideas are broadly consistent with the results of computational studies (Section IX.D). Compounds of type E are described below, while the more highly metallated species are discussed in Sections VII, VIII, and IX. 

Recent studies of the hydrocarbon soluble complexes (jTC5R5)2Cr2(CO)w (R = H, Me) and (n-C5 Hj ) (n-C5Me5 )Cr2 (C0) , that are formulated as having a CrE Cr triple bond, (.51, 52) show that the dominant photoreaction is loss of CO according to equation (12) (53). The tricarbonyl species accounts for the... 

The objectives of this study were to extend these synthetic methods to the preparation of low molecular weight, hydroxy-terminated polymers containing acetylenic bonds and evaluating these prepolymers in castable solid propellant formulations. Since 2-butyne-l,4-diol was commercially available, the formation of polyacetals from this glycol seemed to be an attractive route to the desired polymers. It was believed that the rigid triple bond would inhibit the cyclic acetal formation observed by the earlier workers with the lower members of the saturated glycol series. Thus, in an acetal interchange reaction a linear polymer (I) should be favored over the cyclic acetal (II) ... 

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