Butadiene molecules

Nickel(O) forms a n-complex with three butadiene molecules at low temperature. This complex rearranges spontaneously at 0 °C to afford a bisallylic system, from which a large number of interesting olefins can be obtained. The scheme given below and the example of the synthesis of the odorous compound muscone (R. Baker, 1972, 1974 A.P. Kozikowski, 1976) indicate the variability of such rearrangements (P. Heimbach, 1970). Nowadays many rather complicated cycloolefins are synthesized on a large scale by such reactions and should be kept in mind as possible starting materials, e.g. after ozonolysis. 

There is a mismatch between the ends of the HOMO of one 1 3 butadiene molecule and the LUMO of the other (Fig 10 10) The reaction is forbidden... 

An elegant example of a system investigated by UV-visible spectroscopy is the copolymer of styrene (molecule 1) and 1-chloro-l, 3-butadiene (molecule 2). These molecules quantitatively degrade with the loss of HCl upon heating in base solution. This restores 1,3-unsaturation to the butadiene repeat unit ... 

Another example of such a behavior is provided by the interesting polymerization of butadiene molecules imprisoned in tubes of clathrates of urea.9 Of course, the configuration of the resulting polymer is strongly influenced by the order introduced in the assembly of monomers and thus all trans polybutadiene is formed. 

Fain, J., and Matsen, F. A., J. Chem. Phys. 26, 376, Complete -electron treatment of the butadiene molecule and ion." Complete VB. Results in agreement with SCF with superposition of configurations. 

In conjugated systems the it orbitals become delocalized. The classical example is die butadiene molecule, that is usually described by the formula CH2—CH-CHa=CH2> This representation of the molecule does not take into consideration the delocalization of the 7T-electron system formed by the four... 

These values of the reaction rate constants differ from those cited by Pannetier and Souchay (6) because these individuals erroneously treated the two reactions as if they were of the simple parallel type instead of as if there were a competition between the acrolein and butadiene molecules for other butadiene molecules. 

Treating the jr-system butadiene molecule with a HMO (Hiickel molecular orbital) approach, we get four MOs, which are linear combinations of the four atomic p orbitals... 

Figure 17. Distribution of the electric dipole moments of trani-butadiene molecules, at a density of 1.87 g/cm, calculated just before the occurrence of the polymerization reaction.

Within the two groups of isomers formed, the alkyl perturbation favors the formation of ttc isomers whereas the introduction of nitrogen atoms favors the formation of ttt isomers. It is noteworthy that 1,2- dimethylenecyclohexane reacts with two butadiene molecules to form the ttc- and even the substituted ccc isomer (observed for the first time in a catalytic reaction - for unresolved problems see Sect. 2.5) rather than the tcc isomer. 

The diene exists primarily in a trans conformation, the cis conformer being approximately 2 kcal/mol less stable and separated from the trans conformer by a low energy barrier. At room temperature, only about 5% of butadiene molecules will be in a cis conformation. Clearly, tran -butadiene cannot undergo cycloaddition (as a diene), at least via the concerted pathway which is known to occur, and rotation into a cis conformation is required before reaction can proceed. 

Slade and Jonassen (192) treated ethyleneplatinous chloride, [Pt2Cl4-(C2H4)2], with butadiene, and obtained an unstable complex to which they ascribed the chlorine-bridged structure (XXXIV), on the evidence that its infrared spectrum showed a weak absorption at 1608 cm-1 due to the free double bond of each butadiene molecule. 

The reversal of reactivity is caused by the less steric and polar factors in the interaction of butadiene molecules with an active anionic center. 

Studies by Teplyakov et al. provided the experimental evidence for the formation of the Diels-Alder reaction product at the Si(100)-2 x 1 surface [239,240]. A combination of surface-sensitive techniques was applied to make the assignment, including surface infrared (vibrational) spectroscopy, thermal desorption studies, and synchrotron-based X-ray absorption spectroscopy. Vibrational spectroscopy in particular provides a molecular fingerprint and is useful in identifying bonding and structure in the adsorbed molecules. An analysis of the vibrational spectra of adsorbed butadiene on Si(100)-2 x 1 in which several isotopic forms of butadiene (i.e., some of the H atoms were substituted with D atoms) were compared showed that the majority of butadiene molecules formed the Diels-Alder reaction product at the surface. Very good agreement was also found between the experimental vibrational spectra obtained by Teplyakov et al. [239,240] and frequencies calculated for the Diels-Alder surface adduct by Konecny and Doren [237,238]. 

The titanium trichloride-diethylaluminum chloride catalyst converted butadiene to the cis-, trans,-trans-cyclododecatriene. Professor Wilke and co-workers found that the particular structure is influenced by coordination during cyclization between the transition metal and the growing diene molecules. Analysis of the influence of the ionicity of the catalyst shows effects on the oxidation and reduction of the alkyls and on the steric control in the polymerization. The lower valence of titanium is oxidized by one butadiene molecule to produce only a cis-butadienyl-titanium. Then the cationic chain propagation adds two trans-butadienyl units until the stereochemistry of the cis, trans, trans structure facilitates coupling on the dialkyl of the titanium and regeneration of the reduced state of titanium (Equation 14). 

The tris-allyl complex, in each case, produced a 1.2 growth step of the butadiene molecule. With the more anionic (or less cationic) cobalt salt, the growth occured to only the dimer before it underwent anionic hydride chain transfer. With less anionic chromium the 1.2 chain growth continued on the produce polymer. 

Figure 24.7 shows the TDS results of 1,3-butadiene from clean and carbide-modified V(110). In contrast to those observed for /z-butane, the fraction of 1,3-butadiene molecules undergoing decomposition is reduced... 

If we now look at the cycloaddition of two butadiene molecules to each other (Figure 11.5), we find that because of the symmetry mismatch between the HOMO of one molecule and the LUMO of the other, there can be no stabilization. The only interaction is between filled levels, which, as we have seen in Section 10.1, p. 540, is destabilizing. Hence this process should not occur readily, a conclusion that is again in agreement with experiment. 

Figure 11.5 The approach of two butadiene molecules. The symmetries do not permit HOMO-LUMO interaction the interaction between filled levels, permitted by the symmetry, gives no stabilization.

Analyze the reaction of two butadiene molecules by the Woodward-Hoffmann rules by examining the symmetry properties of the highest occupied molecular orbital (HOMO) of one diene and the lowest unoccupied molecular orbital (LUMO) of the other. 

An understanding of the mechanism of this reaction was obtained by isolation of the intermediate involved. The coupling of three butadiene molecules produces a 12-membered carbon chain bonded to an atom of nickel by two terminal 77-allyl groups (70, 71). 

The 4% single-m-butadiene which is present in butadiene at 20° C reacts to produce almost 8% of octatriene [the formation of a cobalt complex from two single-m-butadiene molecules (0.2%) has been neglected]. 

The scheme shown in Eq. (46) summarizes and explains mechanistically the results so far obtained. Two butadiene molecules may be supposed to react together to form a bis(7r-allyl) C8 chain bonded to the Ni-ligand moiety. This bis(7r-allyl) system exists in two configurations, (XLIII) and (XLIV), from which DVCB and COD are formed. The nature of the ligand in these intermediates seems to be relatively unimportant. 

The formation of the different co-oligomers is not only controlled by the butadiene and alkyne concentration or the choice of catalyst, but is also dependent on the nature of the substituents on the alkyne or on the butadiene (96). It has been found that the formation of a ten-membered ring from a substituted alkyne and two butadiene molecules with a nickel-... 

The results of the particle in a one-dimensional box problem can be used to describe the delocalized n electrons in (linear) conjugated polyenes. Such an approximation is called the free-electron model. Take the butadiene molecule CH2=CH-CH=CH2 as an example. The four n electrons of this system would fill up the [Pg.16]

Figure 4-6. Plane wave convergence of the carbon-carbon bond length in the ethylene and butadiene molecules, from the simulations with the CPMD program13 (Troullier-Martins pseudopotentials,1415 time step 4 a.u., fictitious mass 400 a.u., unit cell 12 A x 12 A x 12 A)...

The initiation was assumed to occur by formation of the disodium adduct followed by fraws-metallation with toluene because no octane was found in the polymeric oils, a product which must arise by addition of a butadiene molecule to the disodium adduct. The transfer step is necessary to explain the very low carboxyl content of the polymer. 

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