Full Geometry Optimizations of Bond-Stretch Isomers of C₂₀²⁺ Fullerene Dication by the Hybrid Density Functional B3LYP Methods

Lee, Ji-Hyun,Lee, Chang-Hoon,Park, Sung-S.,Lee, Kee-Hag Korean Chemical Society 2011 Bulletin of the Korean Chemical Society Vol.32 No.1

We studied the relative stability and atomic structure of five $C_{20}^{2+}$ isomers obtained by two-electron ionization of a $C_{20}$ cage (the smallest fullerene). All the isomers are bond-stretch isomers, i.e., they differ in bond length. In particular, in one of the isomers with Ih symmetry, all the bond lengths are equal. Full geometry optimizations of the dipositive ion $C_{20}^{2+}$ were performed using the hybrid density functional (B3LYP/6-31G(d)) methods. All isomers were found to be true minima by frequency analysis at the level of B3LYP/6-31G(d) under the reinforced tight convergence criterion and a pruned (99,590) grid. The zero-point correction energy for the cage bond-stretch isomers was in the increasing order $D_{2h}<C_{2h}<C_2<T_h<I_h$ of $C_{20}^{2+}$. The energy difference among the isomers of cage dipositive ions was less than that among neutral cage isomers. Our results suggest that these isomers show bond-stretch isomerism and that they have an identical spin state and an identical potential energy curve. Although the predominant electronic configurations of the isomers are similar, the frontier orbital characteristics are different, implying that we could anticipate an entirely different set of characteristic chemical reactions for each type of HOMO and LUMO.

DFT Study for Substitution Patterns of C20H18X2 Regioisomers (X = F, Cl, Br, or OH)

황용규,Seol Lee,이기학 대한화학회 2012 Bulletin of the Korean Chemical Society Vol.33 No.2

We used the hybrid density-functional (B3LYP/6-31G(d,p)) method to analyze the substitution patterns of C20H18X2 derivatives (X = F, Cl, Br, or OH) obtained as disubstituted C20H20 cages. Our results suggest that the cis-1 regioisomers (1,2-dihalo derivatives) are less stable than the trans-1 regioisomers (1,20-dihalo derivatives), whereas in the case of the dihydroxy derivatives, the cis-1 regioisomer is more stable than the trans-1 regioisomer. This implies that in the dihalo-induced strain cages of C20H18X2, the strain effect would affect the relative energies, while in the dihydroxide, the hydrogen bonds have a stronger effect on the relative energies in cis-1 regioisomer than the strain effect do. Thus this supports the experimental result in which the bisvicinal tetrol was of particular preparative-synthetic interest as a substitute for the lacking bisvicinal tetrabromide. Further, the topologies of the HOMO and LUMO characteristics of all C20H18Cl2 and C20H18Br2regioisomers with the same symmetry are same, but they are different from those of C20H18F2 and C20H18(OH)2. This indicates that the five regioisomers of each C20H20 disubstituted derivative will have an entirely different set of characteristic chemical reactions.

Full Geometry Optimizations of Bond-Stretch Isomers of C20^2+ Fullerene Dication by the Hybrid Density Functional B3LYP Methods

Jihyun Lee,이창훈,Sung S. Park,Kee Hag. Lee 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.1

We studied the relative stability and atomic structure of five C_20^2+ isomers obtained by two-electron ionization of a C_20 cage (the smallest fullerene). All the isomers are bond-stretch isomers, i.e., they differ in bond length. In particular, in one of the isomers with Ih symmetry, all the bond lengths are equal. Full geometry optimizations of the dipositive ion C_20^2+ were performed using the hybrid density functional (B3LYP/6-31G(d)) methods. All isomers were found to be true minima by frequency analysis at the level of B3LYP/6-31G(d) under the reinforced tight convergence criterion and a pruned (99,590) grid. The zero-point correction energy for the cage bond-stretch isomers was in the increasing order D_2h < C_2h < C_2 < Th < Ih of C_20^2+ The energy difference among the isomers of cage dipositive ions was less than that among neutral cage isomers. Our results suggest that these isomers show bond-stretch isomerism and that they have an identical spin state and an identical potential energy curve. Although the predominant electronic configurations of the isomers are similar, the frontier orbital characteristics are different,implying that we could anticipate an entirely different set of characteristic chemical reactions for each type of HOMO and LUMO.

Frontier Orbitals of Fifteen C20H17(OH)3 Regioisomers: Hybrid DFT B3LYP Study

이설,이지영,이기학 대한화학회 2013 Bulletin of the Korean Chemical Society Vol.34 No.8

The hybrid density-functional (B3LYP/6-31G(d,p)) method was used to analyze the substitution effect on the C20H20 cage based on calculation of the frontier orbitals of fifteen C20H17(OH)3 derivatives. All substitution products were geometrically optimized without constraints and confirmed by frequency analysis. The results suggest that the cis-1 cis-1 cis-2 regioisomer is the most stable isomer, which implies that hydrogen bonding exerts a stronger effect on the relative energies of the trihydroxide than long-range interactions. Thus, this supports the experimental result in which the bisvicinal tetrol was of particular preparative-synthetic interest. While the LUMO of each of the C20H17(OH)3 regioisomers was equivalently delocalized over the void within the cage, the HOMO was limitedly delocalized on substituents and carbons in close proximity to the substituents. The characteristics of the HOMO of each of the regioisomers vary based on the substitution sites. This indicates that the 15 regioisomers of each C20H20 trisubstituted derivative might undergo an entirely different set of characteristic chemical reactions with electrophilic reagents. The results further suggest that the penta-substituted OH groups on the surface of the fullerene cage are more likely to be localized on a pentagon than to be homogeneously delocalized.

Uptake Effects of Two Electrons for Relative Stability and Atomic Structures of Carbon Cluster Isomers of C₂₀: ab initio Methods

Lee, Wang-Ro,Lee, Chang-Hoon,Kang, Jin-Hee,Park, Sung-Soo,Hwang, Yong-Gyoo,Lee, Kee-Hag Korean Chemical Society 2009 Bulletin of the Korean Chemical Society Vol.30 No.2

This study examined the effect of the uptake of one and two electrons on the atomic structure of three isomers of $C_{20}$ clusters, namely the ring, bowl (corannulene like), and cage (the smallest fullerene). Geometry optimizations were performed using the hybrid density functional (B3LYP) methods for neutral, singly and doubly charged $C_{20},\;{C_{20}}^-,and\;{C_{20}}^{2-}$. These results show that the symmetry of the lowest energies for ring and bowl isomers were not changed, whereas the increasing order of energy for the cage (the smallest fullerene) isomers was changed from $D_{2h}\;<\;C_{2h}\;{\leq}\;C_2\;of\;C_{20}\;through\;Ci\;<\;C_{2h}\;<\;C_2\;<\;D_{2h}\;of\;{C_{20}}^-\;to\;Ci\;<\;C_2\;<\;D_{2h}\;<\;C_{2h}\;of\;{C_{20}}^{2-}$. The reduced symmetry isomers of the cage have comparative energy and the ground state symmetry of the neutral and single and double charged $C_{20}$ decreased with increasing number of electrons taken up in the point of energetics. Interestingly, the difference in energy between the ground state and the next higher energy state of ${C_{20}}^{2-}$ was 3.5kcal/mol, which is the largest energy gap of the neutral, single anion and double anion of the cage isomers examined.

Frontier Orbitals of Fifteen C₂₀H₁₇(OH)₃ Regioisomers: Hybrid DFT B3LYP Study

Lee, Seol,Lee, Ji Young,Lee, Kee Hag Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.8

The hybrid density-functional (B3LYP/6-31G(d,p)) method was used to analyze the substitution effect on the $C_{20}H_{20}$ cage based on calculation of the frontier orbitals of fifteen $C_{20}H_{17}(OH)_3$ derivatives. All substitution products were geometrically optimized without constraints and confirmed by frequency analysis. The results suggest that the cis-1 cis-1 cis-2 regioisomer is the most stable isomer, which implies that hydrogen bonding exerts a stronger effect on the relative energies of the trihydroxide than long-range interactions. Thus, this supports the experimental result in which the bisvicinal tetrol was of particular preparative-synthetic interest. While the LUMO of each of the $C_{20}H_{17}(OH)_3$ regioisomers was equivalently delocalized over the void within the cage, the HOMO was limitedly delocalized on substituents and carbons in close proximity to the substituents. The characteristics of the HOMO of each of the regioisomers vary based on the substitution sites. This indicates that the 15 regioisomers of each $C_{20}H_{20}$ trisubstituted derivative might undergo an entirely different set of characteristic chemical reactions with electrophilic reagents. The results further suggest that the penta-substituted OH groups on the surface of the fullerene cage are more likely to be localized on a pentagon than to be homogeneously delocalized.

Uptake Effects of Two Electrons for Relative Stability and Atomic Structures of Carbon Cluster Isomers of C20: ab initio Methods

이왕로,Changhoon Lee,Jinhee Kang,Sung Soo Park,황용규,이기학 대한화학회 2009 Bulletin of the Korean Chemical Society Vol.30 No.2

This study examined the effect of the uptake of one and two electrons on the atomic structure of three isomers of C20 clusters, namely the ring, bowl (corannulene like), and cage (the smallest fullerene). Geometry optimizations were performed using the hybrid density functional (B3LYP) methods for neutral, singly and doubly charged C20, C20 -, and C20 2-. These results show that the symmetry of the lowest energies for ring and bowl isomers were not changed, whereas the increasing order of energy for the cage (the smallest fullerene) isomers was changed from D2h < C2h ≤ C2 of C20 through Ci < C2h < C2 < D2h of C20 - to Ci < C2 < D2h < C2h of C20 2-. The reduced symmetry isomers of the cage have comparative energy and the ground state symmetry of the neutral and single and double charged C20 decreased with increasing number of electrons taken up in the point of energetics. Interestingly, the difference in energy between the ground state and the next higher energy state of C20 2- was 3.5kcal/mol, which is the largest energy gap of the neutral, single anion and double anion of the cage isomers examined.

Determination of Atomic Structures and Relative Stabilities of Diadduct Regioisomers of C₂₀X₂ (X = H, F, Cl, Br, and OH) by the Hybrid Density-Functional B3LYP Method

Lee, Seol,Suh, Young-Sun,Hwang, Yong-Gyoo,Lee, Kee-Hag Korean Chemical Society 2011 Bulletin of the Korean Chemical Society Vol.32 No.9

We have studied the relative stability and atomic structures of five $C_{20}X_2$ regioisomers obtained as diadducts of a $C_{20}$ cage (X = H, F, Cl, Br, and OH). All the regioisomers are geometric isomers, i.e., they differ in their spatial arrangement. Full-geometry optimizations of the regioisomers have been performed using the hybrid density-functional (B3LYP/6-31G(d, p)) method. Our results suggest that the cis-1 regioisomer (the 1,2-diadduct) is the most stable and that the second most stable is the trans-2 (1,13-diadduct) regioisomer, implying that the long-range interaction between the two adducts and the resonance effect are more pronounced than the diadduct-induced strain in the $C_{20}$ cage. The HOMO and LUMO characteristics of each regioisomer with the same symmetry of structural regioisomers except $C_{20}(OH)_2$ are topologically same. This suggests that by using an entirely different set of characteristic chemical reactions for each regioisomer, we can distinguish between the five regioisomers for each $C_{20}$ diadduct derivative.

DFT Study for Substitution Patterns of C₂₀H₁₈X₂ Regioisomers (X = F, Cl, Br, or OH)

Hwang, Yong-Gyoo,Lee, Seol,Lee, Kee-H. Korean Chemical Society 2012 Bulletin of the Korean Chemical Society Vol.33 No.2

We used the hybrid density-functional (B3LYP/6-31G(d,p)) method to analyze the substitution patterns of $C_{20}H_{18}X_2$ derivatives (X = F, Cl, Br, or OH) obtained as disubstituted $C_{20}H_{20}$ cages. Our results suggest that the cis-1 regioisomers (1,2-dihalo derivatives) are less stable than the trans-1 regioisomers (1,20-dihalo derivatives), whereas in the case of the dihydroxy derivatives, the cis-1 regioisomer is more stable than the trans-1 regioisomer. This implies that in the dihalo-induced strain cages of $C_{20}H_{18}X_2$, the strain effect would affect the relative energies, while in the dihydroxide, the hydrogen bonds have a stronger effect on the relative energies in cis-1 regioisomer than the strain effect do. Thus this supports the experimental result in which the bisvicinal tetrol was of particular preparative-synthetic interest as a substitute for the lacking bisvicinal tetrabromide. Further, the topologies of the HOMO and LUMO characteristics of all $C_{20}H_{18}Cl_2$ and $C_{20}H_{18}Br_2$ regioisomers with the same symmetry are same, but they are different from those of $C_{20}H_{18}F_2$ and $C_{20}H_{18}(OH)_2$. This indicates that the five regioisomers of each $C_{20}H_{20}$ disubstituted derivative will have an entirely different set of characteristic chemical reactions.