Rigid linear structure

The use of alkenyl nitrile oxides is an effective method for the construction of bland polycyclic isoxazolines (2,4,200,236,237). Due to the rigid linear structure of the nitrile oxide, the reaction of alkenyl nitrile oxides almost always proceeds to give bicyclo[X,3,0] derivatives for X = 3-5. Most frequently, the diastereoselec-tivities are controlled by a chiral center on the link between the alkene and the dipole groups. 

Butynediol undergoes the usual reactions of primary alcohols that contribute to its use as a chemical intermediate. Because of its rigid, linear structure, many reactions forming cyclic products from butanediol or m-butenediol give only polymers with butynediol. Both hydroxyl groups can be esterified normally, and the monoesters are readily prepared as mixtures with diesters and unesterified butynediol, but care must be taken in separating them because the monoesters disproportionate easily. 

Not even the SCF procedure can overcome this problem. In the case of atoms, the central field remains a valid and good approximation. Assuming a rigid linear structure in the molecular case is clearly not good enough, although it contains an element of truth. This inherent problem plagues all LCAO-SCF calculations to an even more serious extent. 

Hhis assumption does not imply a rigid linear structure of the diatomic molecule. 2 Obtained by setting m = h = e = 4neo = 1. 

Reactions. Butynediol undergoes the usual reactions of primary alcohols. Because of its rigid, linear structure, many reactions forming cyclic products from butanediol or %-butenediol give only polymers with butynediol. 

A preparative study of four-center type photopolymerization has established the empirical rule that the crystalline state [2- 2] photodimerization of olefins can be widely extended to the crystalline state photopolymerization of diolefins with a rigid linear structure containing conjugated double bonds separated by the 1,4-position of an aromatic ring, such as stilbazol to DSP, or cinnamic derivatives to I,4-phenylenediacrylic (p-PDA) derivatives (O. During the past eighteen years, a great number of photopolymeric diolefin crystals have been found by the use of this empirical rule (see Table I). 

The rigid linear structure has been confirmed for several poly(arylene)s based on the following observations ... 

Thus, we get another glimpse of why D-glucose occupies such a special position in the chemistry of plants and animals. Not only is it the most stable aldohexose (because it can exist in a chair conformation that allows all of its bulky groups to occupy equatorial positions), but its special stereochemistry also allows it to form helical structures when a linked as in starches, and rigid linear structures when /3 linked as in cellulose. 

The CTE values for polyimides from PDA were lower than those of polyimides from 4,4 -ODA, and that of PT(s-BPDA/PDA) (12 ppmK ) was lower than that of PI-(a-BPDA/PDA) (58 ppmK-, due to the rigid linear structure (Table 7.3). PI-(i-BPDA/PDA) was not obtained as a film. 

The CTE values of PI-m-PDAs were lower than those of Pl-m-4,4 -ODA, because of their rigid linear structures. This rigid linear structure is thought to be indispensable for the polyimides with low CTE [51,52], and the CTE values decreased with increasing m in these polyimides (PI-m-4,4 -ODAand PI-m-PDA). However, the CTE values for polyimides have been reported to be dependent on the method for film preparation [53,54]. For example, partially... 

Rigid linear molecules are a special case in which an extended MS group, rather than the MS group, is isomorphic to the point group of the equilibrium structure see chapter 17 of [1]. 

CB), cholesteryl acrylate (CAL) [50]. In their molecular structures listed in Table 4, four tightly conjoining rings are composed of 17 carbon atoms (three rings consist of six carbon atoms, respectively, the fourth of five carbon atoms). Such rings form a comparatively linear and quasi-rigid rodlike structure. 

Figure 91 Rigid, cyclic structure that contains 4,7-phenanthroline and the linear organopalladium complex...

This rigid linear foam with closed cells was developed by ATC Chemicals Company to be used as the core in lightweight structural sandwich composites particularly intended for boatbuilding. SAN foams have ... 

They hypothesized that incorporation of the binding features of this structural water molecule into an inhibitor would be beneficial because of the entropic gain due to its displacement and because the conversion of a flexible linear inhibitor into a rigid, cyclic structure with restricted conformation should provide an additional, positive entropic effect. In the initial design, a cyclohexanone with the ketone oxygen as the structural... 

Timasheff, 1992) for these structures, which can now bind directly between aspartic acids and the flaps, and moreover conversion of a flexible, linear inhibitor into a rigid, cyclic structure with its restriction in conformational freedom would provide an entropic advantage (see Section 2.1). 

Co(N03)2 6H20 are treated with a large excess of sodium 5-phenyl tetrazolate are thought to contain a polymeric complex [Co(5-Ph-tta)2(H20)2] with a molecular weight in the region 104 to 105. A rigid linear chain structure with double tetrazolate bridges is proposed (177). 

A rack-like arrangement schematically represented by 160, would be formed by the complexation of several metal ions to rigid, linear sequences of binding sites. Thus, binding of bipy or phen units to 155 and to its extended tri- and tetratopic analogues present in 157 and in 158 via metal ions of tetrahedral coordination such as Cu(l) and Ag(l) should yield rack structures of type 160. With the bipy or phen unit included in a macrocycle, inorganic rotaxane-type structures (see also Section 9.6) such as 159 have been obtained [9.97a]. A linear sequence of connected terpy sites such as 161 yields racks with individual terpy units and metal ions of octahedral coordination [9.97b]. 

Non therm oprocessihle Condensation Polyimides. These are obtained from condensation of aromatic dianhydrides with aromatic diamines. They are linear noncross-linked resins but their rigid chain structure and strongly hydrogen-bonded character leads to systems which do not melt or soften before decomposition. 

Polymer-analogous variants reach their limits in the face of insufficient rigidity of the functionalised linear polymers which can lead to undesired coiled structures. These have to re-assume a linear structure, with an attendant loss of entropy, in order to assure reaction of all the dendrons with the functional groups attached to the backbone. The dendrons are mostly added in excess in order to facilitate complete reaction, which in turn necessitates tedious purification of the products. The additional steric hindrance occurring on attachment of larger dendrons if higher generation dendrons are already located in the close... 

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