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Fig. 3. Optimized geometries of 6a (front and side view) and 6c, calculated at B3LYP/6-31G*. Hydrogen atoms are removed for clarity (H2-G-H7) is 179.8° for the dimethyldihydropyrene 1; however, in 6a and 6c, the corresponding angles are 159.36° and 159.83°, respectively. Quite similar to H,-G-H7 bond angle, analysis of C>-G-C7 angle delivers the same information. A few important bond angles (H2-G-H,7, C,-G-C,), dihedral angles (1’-10a’-10- 10a) and bond distances (1-1’, 8-8’) for Ga-d and 7a-b are given in Table 1. Both arching type and splitting type distortions are more intense in 6a compared to 6c, which render the former as the most unstable isomer. The other two isomers 6b and 6d, shown in Fig. 5, have only splitting type distortions. A comparison of structural parameters for all isomers is shown in Table 1.

Figure 3 Optimized geometries of 6a (front and side view) and 6c, calculated at B3LYP/6-31G*. Hydrogen atoms are removed for clarity (H2-G-H7) is 179.8° for the dimethyldihydropyrene 1; however, in 6a and 6c, the corresponding angles are 159.36° and 159.83°, respectively. Quite similar to H,-G-H7 bond angle, analysis of C>-G-C7 angle delivers the same information. A few important bond angles (H2-G-H,7, C,-G-C,), dihedral angles (1’-10a’-10- 10a) and bond distances (1-1’, 8-8’) for Ga-d and 7a-b are given in Table 1. Both arching type and splitting type distortions are more intense in 6a compared to 6c, which render the former as the most unstable isomer. The other two isomers 6b and 6d, shown in Fig. 5, have only splitting type distortions. A comparison of structural parameters for all isomers is shown in Table 1.

Related Figures (12)

Fig. 1. Dimethyldihydropyrene 1, non-aromatic model 2 and arenes fused dimethyldihydropyrenes 3-5.
Fig. 1. Dimethyldihydropyrene 1, non-aromatic model 2 and arenes fused dimethyldihydropyrenes 3-5.
Fig. 2. Illustration of steric interaction between peri hydrogens in the [e]-fused bisdihydropyrene (6a), and four possible isomers (6a-d).
Fig. 2. Illustration of steric interaction between peri hydrogens in the [e]-fused bisdihydropyrene (6a), and four possible isomers (6a-d).
Fig. 4. Numbering scheme for the discussion of bis dihydropyrenes. Table 1 Comparison of selected geometric parameters of unbridged [e]-fused bisdihydropyrene 6a-6d and bridged [e]-fused bisdihydropyrnes 7a/b, calculated at B3LYP/6-31G*. All bond lengths and bond angles are in Angstroms and degrees, respectively.
Fig. 4. Numbering scheme for the discussion of bis dihydropyrenes. Table 1 Comparison of selected geometric parameters of unbridged [e]-fused bisdihydropyrene 6a-6d and bridged [e]-fused bisdihydropyrnes 7a/b, calculated at B3LYP/6-31G*. All bond lengths and bond angles are in Angstroms and degrees, respectively.
Fig. 6. Structural drawing of two stereoisomers of 7 (7a and 7b). Fig. 5. The optimized geometries of 6b and 6d, calculated at B3LYP/6-31G*. Hydrogen atoms are removed for clarity. optimized, and the optimized geometries of 7a and 7b are free from arching and splitting type distortions. With the choice of a suitable reference system, the bis-DHP 7 can also be useful in esti- mating the strain energies associated with the isomers 6a-d. the bridged bis-DHP 7 is unstrained. Compound 8 and 9, on the other hand, are not strained. Any difference in energies that arises (E7—-Eg) — (Eg—-Eg) should correspond to the strain energy. The opti- mized structures of 9 and 8 reveal that in 8 is not planar whereas 9 is a planar structure. The non-planarity in 8 is very similar to the observed for isomers 6a-d. The strain energy is calculated by the following formula, and the results are shown in Table 2.
Fig. 6. Structural drawing of two stereoisomers of 7 (7a and 7b). Fig. 5. The optimized geometries of 6b and 6d, calculated at B3LYP/6-31G*. Hydrogen atoms are removed for clarity. optimized, and the optimized geometries of 7a and 7b are free from arching and splitting type distortions. With the choice of a suitable reference system, the bis-DHP 7 can also be useful in esti- mating the strain energies associated with the isomers 6a-d. the bridged bis-DHP 7 is unstrained. Compound 8 and 9, on the other hand, are not strained. Any difference in energies that arises (E7—-Eg) — (Eg—-Eg) should correspond to the strain energy. The opti- mized structures of 9 and 8 reveal that in 8 is not planar whereas 9 is a planar structure. The non-planarity in 8 is very similar to the observed for isomers 6a-d. The strain energy is calculated by the following formula, and the results are shown in Table 2.
Strain energies of 6a-d in kcal mol“! calculated at B3LYP/6-31G"*, through Eq. 1. Table 2
Strain energies of 6a-d in kcal mol“! calculated at B3LYP/6-31G"*, through Eq. 1. Table 2
Fig. 7. Description of the reference model for the estimation of strain energies in 6a-d.
Fig. 7. Description of the reference model for the estimation of strain energies in 6a-d.
'H NMR Chemical shifts of 6a-d and 7a/b and their comparison with the chemical shifts of 3. All chemical shifts are calculated using GIAO-HF/6-31G*//B3LYP/6-31G*. Table 3
'H NMR Chemical shifts of 6a-d and 7a/b and their comparison with the chemical shifts of 3. All chemical shifts are calculated using GIAO-HF/6-31G*//B3LYP/6-31G*. Table 3
NICS values at the centers of Rings for Ga-d, 7a-b and 3. All chemical shifts are calculated using GIAO-HF/6-31G*//B3LYP/6-31G*. Table 4
NICS values at the centers of Rings for Ga-d, 7a-b and 3. All chemical shifts are calculated using GIAO-HF/6-31G*//B3LYP/6-31G*. Table 4
Fig. 9. Description of the reference model for the estimation of steric energy in 10. Fig. 8. Structural drawing of bis CPD 10, CPD-DHP 11 and bridged bis CPD 12.
Fig. 9. Description of the reference model for the estimation of steric energy in 10. Fig. 8. Structural drawing of bis CPD 10, CPD-DHP 11 and bridged bis CPD 12.
Individual bond lengths (A) and the associated bond fixation in 6a-d, 7a-b and 3. (Pakistan). The author also acknowledges Prof Dr. Ralf Ludwig and University of Rostock for generous computational facility. the six membered rings of 6a-d are observed compared to 7aj/k which is again consistent with the supposition that each DHP frag: ment in 6a-d behaves independent of the other, or with very littl influence. Table 5
Individual bond lengths (A) and the associated bond fixation in 6a-d, 7a-b and 3. (Pakistan). The author also acknowledges Prof Dr. Ralf Ludwig and University of Rostock for generous computational facility. the six membered rings of 6a-d are observed compared to 7aj/k which is again consistent with the supposition that each DHP frag: ment in 6a-d behaves independent of the other, or with very littl influence. Table 5
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