TY - JOUR
T1 - A theoretical study of the conformations of tetrabenzo[a,cd,f,lm]perylene, an overcrowded LPAH
AU - Pogodin, Sergey
AU - Agranat, Israel
AU - Fetzer, John C.
PY - 2004
Y1 - 2004
N2 - An overcrowded large polycyclic aromatic hydrocarbon (LPAH) tetrabenzo[a,cd,f,lm]perylene (1) was subjected to an ab initio study. The density functional theory (DFT) B3LYP method was employed to calculate energies and geometries of the stationary point conformations of 1. The global minimum was found to be anti-folded a-Cs-1, while twisted-folded tf-C 2-1 was only 0.2 kJ/mol higher in energy (B3LYP/6-311G**) , giving their equilibrium ratio 52:48 at 25°C. LPAH 1 was compared with its constitutional isomer, tetrabenzo[a,cd,j,lm]perylene (2). The tf-C 2-1 conformation was 10.3 kJ/mol less stable than the corresponding tf-C2-2, while a-Cs-1 was 12.8 kJ/mol more stable than the corresponding a-Ci-2. Nucleus-independent chemical shift (NICS) values, calculated at GIAO-B3LYP/6-31G*// B3LYP/6-31G* are indicative of the aromatic character of the para-terphenyl rings A, F, and A′ of 2, while rings B and C have NICS values close to zero, indicating nonaromatic character. The NICS values are consistent with the Clar pictures of 1 and 2.
AB - An overcrowded large polycyclic aromatic hydrocarbon (LPAH) tetrabenzo[a,cd,f,lm]perylene (1) was subjected to an ab initio study. The density functional theory (DFT) B3LYP method was employed to calculate energies and geometries of the stationary point conformations of 1. The global minimum was found to be anti-folded a-Cs-1, while twisted-folded tf-C 2-1 was only 0.2 kJ/mol higher in energy (B3LYP/6-311G**) , giving their equilibrium ratio 52:48 at 25°C. LPAH 1 was compared with its constitutional isomer, tetrabenzo[a,cd,j,lm]perylene (2). The tf-C 2-1 conformation was 10.3 kJ/mol less stable than the corresponding tf-C2-2, while a-Cs-1 was 12.8 kJ/mol more stable than the corresponding a-Ci-2. Nucleus-independent chemical shift (NICS) values, calculated at GIAO-B3LYP/6-31G*// B3LYP/6-31G* are indicative of the aromatic character of the para-terphenyl rings A, F, and A′ of 2, while rings B and C have NICS values close to zero, indicating nonaromatic character. The NICS values are consistent with the Clar pictures of 1 and 2.
KW - Aromaticity
KW - Density functional theory calculations
KW - Nuclear-independent chemical shifts
KW - Overcrowding
KW - Polycyclic aromatic hydrocarbons
KW - Semiempirical calculations
UR - http://www.scopus.com/inward/record.url?scp=3242729660&partnerID=8YFLogxK
U2 - 10.1080/10406630490460601
DO - 10.1080/10406630490460601
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AN - SCOPUS:3242729660
SN - 1040-6638
VL - 24
SP - 151
EP - 160
JO - Polycyclic Aromatic Compounds
JF - Polycyclic Aromatic Compounds
IS - 3
ER -