Frans-Butadiene

Density functional theory has been used to investigate the Diels-Alder reactions of triazolinedione with s-cis- and. y-fran -butadiene. " Combined quantum mechanics-molecular mechanics calculations have been used to investigate the asymmetric Diels-Alder reaction of cyclopentadiene with the complex dienophiles AICI3-methyl acrylate and methoxyaluminium dichloride-acrolein.Equilibrium constants have been determined for the molecular complexes formed from 1-alkyl-1-(2-naphthyl)ethenes and 1-vinylnaphthalene with TCNE in C1(CH2)2C1 at 27.1 °C ... 

Figure 8.14 Estimates of the pure component spectra for styrene, 1,2-butadiene, c/s-butadiene, and frans-butadiene units in styrene-butadiene polymers, obtained using the CLS method.

In essence, there are only two really important themes in chemistry structure and reactivity. In structural problems, we usually compare the relative stabilities of two isomers (1 and 2) or conformers (3 and 4). Their energy differences are of the order of a few percent. Thus, benzene (1) is more stable than Dewar benzene (2) by 60 kcal mol-1, about 5% of its molecular energy (-1230 kcal mol-1) 3 Similarly, frans-butadiene (3) is more stable than ds-butadiene (4) by 2.7 kcal mol-1, or 3% of its energy of formation. 

By combining high-level ab initio calculations with high-resolution infrared spectroscopy, the equilibrium bond lengths in x-frans-butadiene have been determined to an unprecedented precision of 0.1 pm. The values found for the pair of n-electron delocalized double bonds and the delocalized central single bond are 133.8 and 135.4 pm, respectively. The data provide definitive structural evidence that validates the fundamental concepts of n-electron delocalization, conjugation, and bond alternation in organic chemistry. 

Butadiene, the parent conjugated diene, can in principle attain two planar conformations, namely s-frans-butadiene and. v-m-butadiene. In reality, the majority of the acyclic 1,3-butadiene derivatives exhibit global conformational minima that are at least close to the s-trans-diene situation.1,2 For butadiene itself the s-trans-C4H6 conformer is more stable than the i-cw-isomer by ca. 3 4 kcal mol-1, although the s-trans- - s-cis-butadiene interconversion is kinetically rapid (AG 7 kcal mol-1). Consequently, reactions via the less favorable conformations are not uncommon (e.g., the Diels-Alder reaction) (Scheme 1). 

The electrocyclic interconversion of the cyclobutene 6.47 and the cis, frans-butadiene dicarboxylic ester 6.48 is shown in Fig. 6.8a. The components... 

The epoxidation of terpenic substrates is of interest in the flavor and fragrance industry [55,56]. Terpenes are derivatives of isoprene, which has formula CsHg (2-methyl-frans-butadiene). There are tens of examples of terpenes, including limonene, a-pinene, geraniol, citronellol, myrcene, ocimene, camphene, a-terpin-eol, menthol, and isopugelol. Limonene is an abundant monoterpene extracted from citrus oil, which can be epoxidized to obtain fragrances, perfumes, and... 

FIGURE 8.13 Diagram of acrylonitrile showing cis- and frans-butadiene. 

Scheme 3 Condensed Gibbs free-energy profile (kcal mol ) of the complete catalytic cycle of the co-oligomerization of 1,3-butadiene and ethylene catalyzed by zerovalent bare nickel complexes affording linear and cyclic Cio-olefins, focused on viable routes for individual elementary steps. The favorable [Ni (ri -frans-butadiene)2(ethylene)] isomer of the active catalyst species lb was chosen as reference. Activation barriers for individual steps are given relative to the favorable stereoisomer of the respective precursor (given in italics)...

Poly(1,4-frans-butadiene) Poly(trimethylene oxide)... 

The calculations predict a decay of the population probability of the Bu state of frans-butadiene on a time scale of 30 fs which is in excellent... 

While the — 2 Ag conical intersection in frans-butadiene can be reasonably accurately modeled within the multi-mode vibronic-coupling approach, this is not the case for the 2 Ag — l Ag conical intersection. Several large-amplitude deformations, in particular out-of-plane torsion and... 

Figure 7.5 shows the values of //2i(eo calculated for a pair of fran -butadiene molecules by the point-dipole (Eq. 7.18) and transition-monopole (Eq. 7.15) expressions. In panel A, the orientations of both molecules are held fixed while the center-to-center distance is varied in B the second molecule is rotated at a fixed distance. As a rule of thumb, the point-dipole approximation is reasonably satisfactory if the intermolecular distance is more than 4 or 5 times the length of the chromophores, although the relative error can still be substantial in some situations. 

A strain-crystallizing material like NR shows much better autohesion. It can be processed to a relatively low viscosity for easy wetting on contact, and still exhibit green strength due to strain-induced crystallization. Several other strain-crystallizable elastomers have been synthesized and shown to exhibit autohesion and green strength comparable or superior to that of NR. These include rran.s-polypen-tenamer, fran -butadiene-piperylene elastomers, and uranium-catalyzed polybutadiene. 

Table 7 summarizes several predictions of mid-sized aromatic molecules from the study of Matsuzawa and Dixon. The p value for a molecule with the inversion symmetry operation (benzene) is zero from symmetry arguments. Note that there are sizeable deviations among the experimental observations of p and Y values, as they are also properties difficult to measure. Agreement in Table 7 should be considered reasonably good. Matsuzawa and Dixon have also compared their calculated y values of ethylene, frans-butadiene, and trans-hexatriene with those obtained from ab initio molecular orbital methods the results from their study show that B-LYP calculations are more accurate than those at the Hartree-Fock level and are of comparable accuracy to MP2 results. 

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