Hybridization as a Metric for the Reaction Coordinate of Chemical Reactions

Diels-Alder cycloadditions of butadiene and 1,3-dipolar cycloadditions of azomethine ylide, fulminic acid, and the parent nitrone to polyacenes, fullerenes, and nanotubes have been investigated with density functional theory and ONIOM methods. Activation barriers obtained for cycloaddition reactions on planar and curved systems have been shown to be highly correlated to the energy needed to distort the reactants to the geometry of the transition state (TS).

supporting

confidence: 75%

Cycloaddition Reactions of Butadiene and 1,3‐Dipoles to Curved Arenes, Fullerenes, and Nanotubes: Theoretical Evaluation of the Role of Distortion Energies on Activation Barriers

Osuna

Houk

2009

“…[50] The resulting C 81 Pt 2 heterofullerene contains a tetracoordinate and tricoordinate platinum atom which is similar to the situation in C 57 Pt 2 . Pyramidalisation angles [51,52] and bond lengths of all the different CÀC bonds Table 7 and Figure 8). The values of the four factors used in the prediction are shown in Table 7.…”

Section: Discussionmentioning

confidence: 99%

Prediction of Heterofullerene Stabilities: A Combined DFT and Chemometric Study of C₅₆Pt₂, C₅₇Pt₂and C₈₁Pt₂

Campanera

Balch

et al. 2005

A systematic search of the regioisomers of the heterofullerenes, C57Pt2 and C56Pt2, has been carried out by means of density functional calculations to find the most stable structures. Both heterofullerenes incorporate two metal atoms into the fullerene surface. In the case of C57Pt2, one platinum atom substitutes one carbon atom of C60 and the other platinum atom replaces a C--C bond, whereas in C56Pt2 each platinum atom replaces one C--C bond. Several geometric factors were studied, three of which have particularly important effects on the relative stabilities of the regioisomers: the Pt--Pt separation, the number of C--C bonds remaining after substitution, and the type of C--C bond that is substituted. All these factors indicate that the deformation of the carbon framework is a general factor that governs the relative stabilities of the regioisomers. Because a high number of factors affect the stability of the heterofullerenes we also used chemometric techniques in this study. Partial least-squares (PLS) regression was used to establish the structure-energy relationships of C57Pt2 and C56Pt2 heterofullerenes. The understanding gained of the factors that affect the relative isomers stabilities has allowed us to predict the stabilities of larger disubstituted carbon cages, for example, C81Pt2 heterofullerene.

“…Pyramidalization angles, introduced by Haddon and Chow45 as a measure of the local curvature in polycyclic aromatic hydrocarbons, were calculated with the POAV3 program 46…”

Section: Computational Detailsmentioning

confidence: 99%

Reactivity and Regioselectivity of Noble Gas Endohedral Fullerenes Ng@C₆₀ and Ng₂@C₆₀ (Ng=He–Xe)

Osuna

Swart

Solà

2009

Recently, it was shown that genuine Ng-Ng chemical bonds are present in the endohedral fullerenes Ng(2)@C(60) in the case of Ng=Xe, while it is more debatable whether a chemical bond exist for Ng=Ar and Kr. The lighter homologues with helium and neon are weakly bonded van der Waals complexes. The presence of a noble gas dimer inside the cage is expected to modify the exohedral reactivity of the C(60) cage with respect to that of free C(60). To investigate the impact of encapsulated diatomic noble gas molecules on the chemical reactivity of C(60), we analyzed the thermodynamics and the kinetics of [4+2] Diels-Alder cycloaddition of 1,3-cis-butadiene at all nonequivalent bonds in free C(60), Ng@C(60), and Ng(2)@C(60) (Ng=He, Ne, Ar, Kr, and Xe). Our BP86/TZP calculations reveal that introduction of single noble gas atoms in Ng@C(60) and noble gas dimers He(2) and Ne(2) in Ng(2)@C(60) has almost no effect on the exohedral reactivity compared to free C(60), in agreement with experimental results. In all these cases cycloaddition is clearly favored at the [6,6] bonds in the fullerene cage. For the endohedral compounds He(2)@C(60) and Ne(2)@C(60) a slight preference (by less than 2 kcal mol(-1)) for bonds closer to the C(5) symmetry axis is found. This picture changes dramatically for the endohedral compounds with heavier noble gas dimers. Encapsulation of these noble gas dimers clearly enhances the reaction, both under thermodynamic and kinetic control. Moreover, in the case of Xe(2)@C(60), addition to [6,6] and [5,6] bonds becomes equally viable. These reactivity changes in endohedral fullerenes are attributed to stabilization of the LUMO, increased fullerene strain energy, and greater compression of the encapsulated Ng(2) unit along the He to Xe series.