Butadiene, modeling

There is an even more striking change in the conformational preference of poly-(isoprenyl)lithium on increasing solvent polarity than observed in the poly(butadienyl)-lithium model. There is no detectable trans-carbanion in THF, and even changing solvent from benzene to ether causes a decrease in the trans content from 65 to 25 %. In THF, the exclusively cis conformation is noted 198) for the sodium and potassium ion pair of the isoprene model the butadiene model carbanion is 22% trans with sodium but less than 10% trans with potassium (all at —20 °C). 

For computational reasons, we first focused on the benzene and butadiene models [94], as well as on the Be atom using a very limited basis set. 

Electi ocyclic reactions are examples of cases where ic-electiDn bonds transform to sigma ones [32,49,55]. A prototype is the cyclization of butadiene to cyclobutene (Fig. 8, lower panel). In this four electron system, phase inversion occurs if no new nodes are fomred along the reaction coordinate. Therefore, when the ring closure is disrotatory, the system is Hiickel type, and the reaction a phase-inverting one. If, however, the motion is conrotatory, a new node is formed along the reaction coordinate just as in the HCl + H system. The reaction is now Mdbius type, and phase preserving. This result, which is in line with the Woodward-Hoffmann rules and with Zimmerman s Mdbius-Huckel model [20], was obtained without consideration of nuclear symmetry. This conclusion was previously reached by Goddard [22,39]. 

Examine the models of 1 3 butadiene in Figure 10 6 on Learn mg By Modeling and com pare space filling models of the s CIS and s trans confor mation... 

Concerted Nonpolar Reactions. Maleic anhydride exemplifies the model dienophile for cycloaddition with dienes such as 1,3-butadiene... 

Solubihties of 1,3-butadiene and many other organic compounds in water have been extensively studied to gauge the impact of discharge of these materials into aquatic systems. Estimates have been advanced by using the UNIFAC derived method (19,20). Similarly, a mathematical model has been developed to calculate the vapor—Hquid equiUbrium (VLE) for 1,3-butadiene in the presence of steam (21). 

The rectangular structure is calculated to be strongly destabilized (antiaromatic) with respect to a polyene model. With 6-3IG calculations, for example, cyclobutadiene is found to have a negative resonance energy of—54.7 kcal/mol, relative to 1,3-butadiene. In addition, 30.7 kcal of strain is found, giving a total destabilization of 85.4 kcal/mol. G2 and MP4/G-31(d,p) calculations arrive at an antiaromatic destabilization energy of about 42kcal/mol. ... 

The hetero-Diels-Alder reaction of formaldehyde with 1,3-butadiene has been investigated with the formaldehyde oxygen atom coordinated to BH3 as a model for a Lewis acid [25 bj. Two transition states were located, one with BH3 exo, and one endo, relative to the diene. The former has the lowest energy and the calculated transition-state structure is much less symmetrical than for the uncatalyzed reaction shown in Fig. 8.12. The C-C bond length is calculated to be 0.42 A longer, while the C-0 bond length is 0.23 A shorter, compared to the uncatalyzed reac-... 

A lower max response at resonance was noted for poly butadiene-acrylic acid-containing pro-pints compared with polyurethane-containing opaque proplnts. Comparison of the measured response functions with predictions of theoretical models, which were modified to consider radiant-heat flux effects for translucent proplnts rather than pressure perturbations, suggest general agreement between theory and expt. The technique is suggested for study of the effects of proplnt-formulation variations on solid-proplnt combustion dynamics... 

Butadiene has two n bonds. The interaction between the two n bonds is one of the simplest models to derive molecular orbitals from bond orbitals. A n bond in butadiene is similar to that in ethylene. The n bond is represented by the bonding and antibonding orbitals. The interactions occur between the n bonds in butadiene. The bond interactions are represented by the bond orbital interactions. 

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