- Email: [email protected]
Cyclacenes having mono boron or nitrogen atom in the backbone—a theoretical study
Journal of Molecular Structure (Theochem) 674 (2004) 185–189 www.elsevier.com/locate/theochem
Cyclacenes having mono boron or nitrogen atom in the backbone— a theoretical study Lemi Tu¨rker*, Selc¸uk Gu¨mu¨s¸ Department of Chemistry, Middle East Technical University, 06531 Ankara, Turkey Received 10 September 2003; accepted 14 November 2003
Abstract Semi-empirical molecular orbital treatment at the level of AM1 unrestricted Hartree – Fock type calculations was performed on the Hu¨ckel type boron and nitrogen substituted cyclacenes. Substitution is done either in a peri position or a fusion points. Boron substitution is found to be destabilizing, whereas nitrogen substitution has stabilizing effect on parent cyclacenes. q 2003 Elsevier B.V. All rights reserved. Keywords: Boron substituted; Nitrogen substituted; Cyclacenes; AM calculations
1. Introduction Cyclacenes (Fig. 1) can be obtained, theoretically, by intramolecular union process of acenes, which are linearly annelated benzene rings [1]. However, this cyclization process distorts the p-conjugation depending on the size of the structure. Cyclacenes have been studied by many theoretical and experimental chemists [2 –18] since they are interesting systems in relation to both carbon nanotubes and molecular wires [19,20]. Cyclacenes can be characterized by the presence of two distinct p-systems in their structures. First one is the benzenoid rings forming the main backbone and the second is the top and bottom peripheral circuits, which can be either 4m or 4m þ 2 type depending on the number of benzenoid rings (R) in the structure. According to theoretical investigations some properties of cyclacenes should result from the predominating effect of the peripheral circuits. Moreover, cyclacenes are classified as Hu¨ckel and Mobius types depending on the number of phase dislocations ðkÞ that the structure possesses. Hu¨ckel type cyclacenes have even number of phase dislocations (including zero) whereas Mobius types possess odd values. * Corresponding author. E-mail address: [email protected] (L. Tu¨rker). 0166-1280/$ - see front matter q 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.theochem.2003.11.040
Centric perturbations on the backbone of the parent cyclacene may result in very interesting p-systems. For instance, boron is the unique element of the group III of the periodic table that can form aromatic compounds. Nitrogen, on the other hand, possesses complexation sites. Both boron and nitrogen embedded structures of cyclacenes should possess interesting systems, exhibiting interesting properties. The present study deals with the AM1 unrestricted Hartree –Fock (UHF) treatment of the mono-boron and nitrogen substituted Hu¨ckel type cyclacenes having R ¼ 3 – 8: Boron or nitrogen are embedded either in a peri position or a fusion point.
2. Method In the present treatise, the geometry optimizations of all the structures leading to energy minima were achieved by using the AM1 (Austin model 1) self-consistent fields molecular orbital (SCF MO) [21] method at the UHF level. The optimizations were obtained by the application of a conjugate gradient method, Polak-Ribiere (convergence limit of 4.18 £ 1024 kJ/mol (0.0001 kcal/mol) and RMS gradient of 4.18 £ 107 kJ/m mol (0.001 kcal/(A mol))). All these calculations were performed by using the Hyperchem (release 5.1) program.
L. Tu¨rker, S. Gu¨mu¨s¸ / Journal of Molecular Structure (Theochem) 674 (2004) 185–189
186
Fig. 1. Structure of a cyclacene having R ¼ 7:
3. Results and discussion The geometry optimized structures of the presently considered cyclacenes are given in Fig. 2. Four types of structures are investigated in this study: (I) cyclacenes having a boron atom, embedded at a fusion point represented as B – F, (II) boron embedded cyclacenes at a peri position represented as B – P, (III) nitrogen embedded cyclacenes at a fusion point represented as N –F and (IV) nitrogen embedded cyclacenes at a peri position represented as N –P. When charge developments on each atom are investigated the following results are obtained. In the case of B – F cyclacenes, boron, carbon, and hydrogen atoms possess positive, negative and positive charge development, respectively, except for R ¼ 6 in which some of the carbon atoms at bottom and upper peripheries are positively
charged. Therefore, the position of the boron atom (the top and bottom peripheral circuits) does not effect the charges on the atoms except for R ¼ 6: For B –P case negative charge development is observed on boron atom only for R ¼ 3; and for the rest of the series boron possesses positive charge development. Some of the carbon atoms are negative, positive and zero charged and hydrogens are either positively or zero charged for the series of compounds. Thus, the size of the ring and the position of the boron atom are very important factors affecting the charge developments on atoms in the case of boron embedded cyclacenes at a peri position. Cyclacenes nitrogen substituted at a fusion point (N– F) result negatively charged nitrogen and carbon, and positively charged hydrogen atoms in the series R ¼ 3 – 8: So, no effect of the position of the nitrogen is observed for N –-F type structures. In the case of N – P type cyclacenes nitrogen possesses positive charge for R ¼ 3; 4 and negative for the rest. Whereas carbon atoms possess positive, negative or zero charge and hydrogens are either positively or zero charged. 3.1. The stabilities Total energy/R values of various boron and nitrogen substituted cyclacenes are given in Table 1. Among all the systems, nitrogen embedded structures at the fusion point
Fig. 2. Structures of the presently considered structures for R ¼ 6: I, II, III, IV are B –F, B–P, N–F, N–P, respectively.
L. Tu¨rker, S. Gu¨mu¨s¸ / Journal of Molecular Structure (Theochem) 674 (2004) 185–189 Table 1 Total energy/R values for the four types under investigation (energies in kJ/mol)
187
Table 3 DHf values (in kJ/mol) for various boron and nitrogen embedded cyclacenes Boron substituted
Boron substituted
Nitrogen substituted
Nitrogen substituted
R
F
P
F
P
3 4 5 6 7 8
249712 250334 250721 250940 251142 251261
249222 249980 250429 250730 250935 251084
254153 253656 253367 253180 253045 252931
253651 253311 253115 252960 252853 252765
R
F
P
F
P
3 4 5 6 7 8
1578 1504 1356 1447 1220 1249
1731 1600 1501 1387 1350 1340
1541 1503 1413 1292 1185 1175
1731 1564 1357 1257 1206 1185
3.2. The frontier molecular orbital energies (N –F) are the most stable ones. Boron embedded structures at the fusion point (B –F) are more stable than the boron substituted cyclacenes at the peri position (B– P). Mono boron substituted cyclacenes get more and more stable as R increases for both B – P and B –F types, that is reasonable, because as the number of rings increases benzenoid rings forming the main backbone become flatter, allowing a much better p-conjugation. Whereas for monoazacyclacenes it is just the reverse, that is, as the ring size increases both N –F and N – P types become less stable. Among all the structures no cryptoannulenic effect is observed for total energy/R values. Table 2 shows the binding energy/R values for the structures under consideration. As seen in Table 2 the binding energy/R values become more negative as R increases for all the structures, revealing that the greater the ring size the better the stability of the molecule. Heats of formation values for various mono boron or mono nitrogen atom having cyclacenes are tabulated in Table 3. All of the structures are endothermic. As the ring size increases DHf values decrease so, the structures become less and less endothermic for B – P, N –F, and N – P. Whereas in the case of B – F, DHf values decrease and increase alternatingly such that the peripheral circuits of 4m type are more endothermic, thus, a cryptoannulenic effect can be pronounced for these structures except for R ¼ 3:
Table 2 Binding energy/R values for the four types under investigation (energies in kJ/mol)
The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels as well as their differences DE (the interfrontier energy gap) are shown in Table 4. As Table 4 reveals the HOMO, LUMO and DE values fluctuate randomly. The HOMO and LUMO energy schemes can be seen in Fig. 3 for R ¼ 5: Note that in all structures the heteroatom contributes to the LUMO orbital, whereas, no contribution to the HOMO orbital is observed except for B – P type cyclacenes. 3.3. Some structural and physicochemical properties Table 5 gives some structural and physicochemical properties of the boron and nitrogen substituted cyclacenes.
Table 4 LUMO, HOMO and DE values for various boron and nitrogen substituted cyclacenes (in each case the first, second, and third entries are LUMO, HOMO and DE; respectively) Boron substituted R
3
4
5 Boron substituted
Nitrogen substituted
R
F
P
F
P
3 4 5 6 7 8
22720.72 22881.14 22888.77 23030.3 23100.66 23121.46
22597.19 22804.61 22922.62 23003.94 23050.89 23082.88
22701.41 22859.79 22964.98 23040.23 23092.03 23118.78
22565.65 22789.99 22932.54 23009.73 23057.93 23090.39
6
7
8
Nitrogen substituted
F
P
F
P
21.50 215.40 13.90 20.78 214.50 13.72 20.93 213.98 13.00 20.10 214.07 13.97 20.07 213.15 13.08 20.12 212.97 12.85
21.18 215.06 12.88 21.41 215.20 13.79 20.94 214.62 13.68 20.27 214.51 14.24 20.37 214.20 13.83 20.45 214.29 13.84
21.04 214.42 13.38 20.60 214.30 13.70 20.96 214.27 13.31 22.55 212.92 10.37 0.10 214.04 14.14 21.24 213.63 12.39
21.52 215.29 13.77 21.14 214.66 13.52 20.75 214.29 13.54 20.77 213.82 13.05 20.78 213.72 12.94 20.90 213.71 12.81
188
L. Tu¨rker, S. Gu¨mu¨s¸ / Journal of Molecular Structure (Theochem) 674 (2004) 185–189
Fig. 3. HOMO LUMO schemes of structures under consideration for R ¼ 5:
The polarizability is estimated from an additivity scheme presented by Miller [22]. Note that the polarizability/R values are almost constant (7.0 £ 10230 m3) for all the cyclacenes of present consideration. The dipole moments fluctuate randomly for both boron and nitrogen embedded cyclacenes. Monoazacyclacenes at peri position (N– P) has the highest dipole moment among all.
4. Conclusion The results of the AM1 UHF type semi empirical calculation reveal that the structures considered presently should be stable but endothermic. The structures possess no cryptoannulenic effect for total energy/R and binding energy/R values. As for the heats of
L. Tu¨rker, S. Gu¨mu¨s¸ / Journal of Molecular Structure (Theochem) 674 (2004) 185–189 Table 5 Some structural and physicochemical parameters of various cyclacenes Boron substituted F
P
F
P
3
3.53 300.74 464.74 21.19 1.74 347.95 568.43 28.46 4.79 386.81 667.55 35.28 9.75 430.82 780.65 43.00 0.57 485.64 900.19 50.27 1.04 536.36 1026.02 57.54
0.74 283.44 432.15 21.35 0.31 342.47 555.97 28.62 0.53 374.49 637.56 35.89 0.65 420.37 748.75 43.16 0.62 465.84 863.41 50.43 0.59 532.67 1016.84 57.70
2.24 300.78 460.48 21.00 1.01 345.80 560.03 28.27 2.76 387.08 665.46 35.54 2.13 432.58 776.32 42.81 2.63 479.03 891.45 50.08 2.52 535.10 1013.48 57.35
8.08 293.95 451.91 21.10 6.30 321.65 515.70 28.37 6.56 356.66 621.61 35.64 6.36 420.67 739.14 42.91 6.21 460.87 853.55 50.18 6.11 540.52 1009.46 57.45
5
6
7
8
the preceding and following 4m þ 2 type system within the homologous series.
Nitrogen substituted
R
4
189
In each case the first, second, third and forth entries are dipole moment, area, volume and polarizability values, respectively (Dipole moments in the order of 10230 C.m., area in the order of 10220 m2, volume in the order of 10230 m3, and polarizability in the order of 10230 m3).
formation, B –P, N –F, N – P type structures become less endothermic as R increases. Whereas B – F type structures possess the cryptoannulenic effect such that a 4m-type system is more endothermic than
References [1] M.J.S. Dewar, R.C. Dougherty, PMO Theory of Organic Chemistry, Plenum Press, New York, 1975. [2] I. Agranat, B.A. Hess Jr., L.J. Schaad, Pure Appl. Chem. 52 (1980) 1399. [3] J.L. Bergan, B.N. Cyvin, S.J. Cyvin, Acta Chim. Hung. 124 (1987) 299. [4] G. Ege, H. Vogler, Theor. Chim. Acta 35 (1974) 189. [5] E. Heilbronner, Helv. Chim. Acta 37 (1954) 921. [6] G. Derflinger, H. Sofer, Monatch. Chem. 99 (1968) 1866. [7] S. Kivelson, O.L. Chapman, Phys. Rev. B 28 (1983) 7326. [8] F.J. Zhang, S.J. Cyvin, B.N. Cyvin, Monatch. Chem. 121 (1990) 421. [9] P.R. Ashton, N.S. Isaac, F.H. Kohnke, A.M.Z. Slawin, C.M. Spencer, J.F. Stoddart, D.J. Williams, Angew. Chem. Int. Ed. Engl. 27 (1988) 966. [10] R.W. Alder, R.B. Sessions, J. Chem. Soc. Perkin Trans. 2 (1985) 1849. [11] R.O. Angus Jr., R.P. Johnson, J. Org. Chem. 53 (1988) 314. [12] L. Tu¨rker, Polycycl. Aromatic Compd 4 (1994) 191. [13] L. Tu¨rker, Polycycl. Aromatic Compd 8 (1996) 67. [14] L. Tu¨rker, Polycycl. Aromatic Compd 4 (1995) 231. [15] L. Tu¨rker, Polycycl. Aromatic Compd 8 (1996) 203. [16] L. Tu¨rker, J. Mol. Struct. (Theochem) 407 (1997) 217. [17] L. Tu¨rker, J. Mol. Struct. (Theochem) 454 (1998) 83. [18] I. Gutman, P.U. Biederman, V.I. Petrovic, I. Agranat, Polycycl. Aromatic Compd 8 (1996) 189. [19] S. Iijima, Nature 354 (1991) 56. [20] G. Overney, W. Zhong, D. Tomainek, Zeitschrift fur Physik D 27 (1993) 93. [21] M.J.S. Dewar, E.G. Zoebisch, E.F. Healey, J.J.P. Steward, J. Am. Chem. Soc. 107 (1985) 3902. [22] K.J. Miller, J. Am. Chem. Soc. 112 (1990) 8533.
Cyclacenes having mono boron or nitrogen atom in the backbone— a theoretical study Lemi Tu¨rker*, Selc¸uk Gu¨mu¨s¸ Department of Chemistry, Middle East Technical University, 06531 Ankara, Turkey Received 10 September 2003; accepted 14 November 2003
Abstract Semi-empirical molecular orbital treatment at the level of AM1 unrestricted Hartree – Fock type calculations was performed on the Hu¨ckel type boron and nitrogen substituted cyclacenes. Substitution is done either in a peri position or a fusion points. Boron substitution is found to be destabilizing, whereas nitrogen substitution has stabilizing effect on parent cyclacenes. q 2003 Elsevier B.V. All rights reserved. Keywords: Boron substituted; Nitrogen substituted; Cyclacenes; AM calculations
1. Introduction Cyclacenes (Fig. 1) can be obtained, theoretically, by intramolecular union process of acenes, which are linearly annelated benzene rings [1]. However, this cyclization process distorts the p-conjugation depending on the size of the structure. Cyclacenes have been studied by many theoretical and experimental chemists [2 –18] since they are interesting systems in relation to both carbon nanotubes and molecular wires [19,20]. Cyclacenes can be characterized by the presence of two distinct p-systems in their structures. First one is the benzenoid rings forming the main backbone and the second is the top and bottom peripheral circuits, which can be either 4m or 4m þ 2 type depending on the number of benzenoid rings (R) in the structure. According to theoretical investigations some properties of cyclacenes should result from the predominating effect of the peripheral circuits. Moreover, cyclacenes are classified as Hu¨ckel and Mobius types depending on the number of phase dislocations ðkÞ that the structure possesses. Hu¨ckel type cyclacenes have even number of phase dislocations (including zero) whereas Mobius types possess odd values. * Corresponding author. E-mail address: [email protected] (L. Tu¨rker). 0166-1280/$ - see front matter q 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.theochem.2003.11.040
Centric perturbations on the backbone of the parent cyclacene may result in very interesting p-systems. For instance, boron is the unique element of the group III of the periodic table that can form aromatic compounds. Nitrogen, on the other hand, possesses complexation sites. Both boron and nitrogen embedded structures of cyclacenes should possess interesting systems, exhibiting interesting properties. The present study deals with the AM1 unrestricted Hartree –Fock (UHF) treatment of the mono-boron and nitrogen substituted Hu¨ckel type cyclacenes having R ¼ 3 – 8: Boron or nitrogen are embedded either in a peri position or a fusion point.
2. Method In the present treatise, the geometry optimizations of all the structures leading to energy minima were achieved by using the AM1 (Austin model 1) self-consistent fields molecular orbital (SCF MO) [21] method at the UHF level. The optimizations were obtained by the application of a conjugate gradient method, Polak-Ribiere (convergence limit of 4.18 £ 1024 kJ/mol (0.0001 kcal/mol) and RMS gradient of 4.18 £ 107 kJ/m mol (0.001 kcal/(A mol))). All these calculations were performed by using the Hyperchem (release 5.1) program.
L. Tu¨rker, S. Gu¨mu¨s¸ / Journal of Molecular Structure (Theochem) 674 (2004) 185–189
186
Fig. 1. Structure of a cyclacene having R ¼ 7:
3. Results and discussion The geometry optimized structures of the presently considered cyclacenes are given in Fig. 2. Four types of structures are investigated in this study: (I) cyclacenes having a boron atom, embedded at a fusion point represented as B – F, (II) boron embedded cyclacenes at a peri position represented as B – P, (III) nitrogen embedded cyclacenes at a fusion point represented as N –F and (IV) nitrogen embedded cyclacenes at a peri position represented as N –P. When charge developments on each atom are investigated the following results are obtained. In the case of B – F cyclacenes, boron, carbon, and hydrogen atoms possess positive, negative and positive charge development, respectively, except for R ¼ 6 in which some of the carbon atoms at bottom and upper peripheries are positively
charged. Therefore, the position of the boron atom (the top and bottom peripheral circuits) does not effect the charges on the atoms except for R ¼ 6: For B –P case negative charge development is observed on boron atom only for R ¼ 3; and for the rest of the series boron possesses positive charge development. Some of the carbon atoms are negative, positive and zero charged and hydrogens are either positively or zero charged for the series of compounds. Thus, the size of the ring and the position of the boron atom are very important factors affecting the charge developments on atoms in the case of boron embedded cyclacenes at a peri position. Cyclacenes nitrogen substituted at a fusion point (N– F) result negatively charged nitrogen and carbon, and positively charged hydrogen atoms in the series R ¼ 3 – 8: So, no effect of the position of the nitrogen is observed for N –-F type structures. In the case of N – P type cyclacenes nitrogen possesses positive charge for R ¼ 3; 4 and negative for the rest. Whereas carbon atoms possess positive, negative or zero charge and hydrogens are either positively or zero charged. 3.1. The stabilities Total energy/R values of various boron and nitrogen substituted cyclacenes are given in Table 1. Among all the systems, nitrogen embedded structures at the fusion point
Fig. 2. Structures of the presently considered structures for R ¼ 6: I, II, III, IV are B –F, B–P, N–F, N–P, respectively.
L. Tu¨rker, S. Gu¨mu¨s¸ / Journal of Molecular Structure (Theochem) 674 (2004) 185–189 Table 1 Total energy/R values for the four types under investigation (energies in kJ/mol)
187
Table 3 DHf values (in kJ/mol) for various boron and nitrogen embedded cyclacenes Boron substituted
Boron substituted
Nitrogen substituted
Nitrogen substituted
R
F
P
F
P
3 4 5 6 7 8
249712 250334 250721 250940 251142 251261
249222 249980 250429 250730 250935 251084
254153 253656 253367 253180 253045 252931
253651 253311 253115 252960 252853 252765
R
F
P
F
P
3 4 5 6 7 8
1578 1504 1356 1447 1220 1249
1731 1600 1501 1387 1350 1340
1541 1503 1413 1292 1185 1175
1731 1564 1357 1257 1206 1185
3.2. The frontier molecular orbital energies (N –F) are the most stable ones. Boron embedded structures at the fusion point (B –F) are more stable than the boron substituted cyclacenes at the peri position (B– P). Mono boron substituted cyclacenes get more and more stable as R increases for both B – P and B –F types, that is reasonable, because as the number of rings increases benzenoid rings forming the main backbone become flatter, allowing a much better p-conjugation. Whereas for monoazacyclacenes it is just the reverse, that is, as the ring size increases both N –F and N – P types become less stable. Among all the structures no cryptoannulenic effect is observed for total energy/R values. Table 2 shows the binding energy/R values for the structures under consideration. As seen in Table 2 the binding energy/R values become more negative as R increases for all the structures, revealing that the greater the ring size the better the stability of the molecule. Heats of formation values for various mono boron or mono nitrogen atom having cyclacenes are tabulated in Table 3. All of the structures are endothermic. As the ring size increases DHf values decrease so, the structures become less and less endothermic for B – P, N –F, and N – P. Whereas in the case of B – F, DHf values decrease and increase alternatingly such that the peripheral circuits of 4m type are more endothermic, thus, a cryptoannulenic effect can be pronounced for these structures except for R ¼ 3:
Table 2 Binding energy/R values for the four types under investigation (energies in kJ/mol)
The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels as well as their differences DE (the interfrontier energy gap) are shown in Table 4. As Table 4 reveals the HOMO, LUMO and DE values fluctuate randomly. The HOMO and LUMO energy schemes can be seen in Fig. 3 for R ¼ 5: Note that in all structures the heteroatom contributes to the LUMO orbital, whereas, no contribution to the HOMO orbital is observed except for B – P type cyclacenes. 3.3. Some structural and physicochemical properties Table 5 gives some structural and physicochemical properties of the boron and nitrogen substituted cyclacenes.
Table 4 LUMO, HOMO and DE values for various boron and nitrogen substituted cyclacenes (in each case the first, second, and third entries are LUMO, HOMO and DE; respectively) Boron substituted R
3
4
5 Boron substituted
Nitrogen substituted
R
F
P
F
P
3 4 5 6 7 8
22720.72 22881.14 22888.77 23030.3 23100.66 23121.46
22597.19 22804.61 22922.62 23003.94 23050.89 23082.88
22701.41 22859.79 22964.98 23040.23 23092.03 23118.78
22565.65 22789.99 22932.54 23009.73 23057.93 23090.39
6
7
8
Nitrogen substituted
F
P
F
P
21.50 215.40 13.90 20.78 214.50 13.72 20.93 213.98 13.00 20.10 214.07 13.97 20.07 213.15 13.08 20.12 212.97 12.85
21.18 215.06 12.88 21.41 215.20 13.79 20.94 214.62 13.68 20.27 214.51 14.24 20.37 214.20 13.83 20.45 214.29 13.84
21.04 214.42 13.38 20.60 214.30 13.70 20.96 214.27 13.31 22.55 212.92 10.37 0.10 214.04 14.14 21.24 213.63 12.39
21.52 215.29 13.77 21.14 214.66 13.52 20.75 214.29 13.54 20.77 213.82 13.05 20.78 213.72 12.94 20.90 213.71 12.81
188
L. Tu¨rker, S. Gu¨mu¨s¸ / Journal of Molecular Structure (Theochem) 674 (2004) 185–189
Fig. 3. HOMO LUMO schemes of structures under consideration for R ¼ 5:
The polarizability is estimated from an additivity scheme presented by Miller [22]. Note that the polarizability/R values are almost constant (7.0 £ 10230 m3) for all the cyclacenes of present consideration. The dipole moments fluctuate randomly for both boron and nitrogen embedded cyclacenes. Monoazacyclacenes at peri position (N– P) has the highest dipole moment among all.
4. Conclusion The results of the AM1 UHF type semi empirical calculation reveal that the structures considered presently should be stable but endothermic. The structures possess no cryptoannulenic effect for total energy/R and binding energy/R values. As for the heats of
L. Tu¨rker, S. Gu¨mu¨s¸ / Journal of Molecular Structure (Theochem) 674 (2004) 185–189 Table 5 Some structural and physicochemical parameters of various cyclacenes Boron substituted F
P
F
P
3
3.53 300.74 464.74 21.19 1.74 347.95 568.43 28.46 4.79 386.81 667.55 35.28 9.75 430.82 780.65 43.00 0.57 485.64 900.19 50.27 1.04 536.36 1026.02 57.54
0.74 283.44 432.15 21.35 0.31 342.47 555.97 28.62 0.53 374.49 637.56 35.89 0.65 420.37 748.75 43.16 0.62 465.84 863.41 50.43 0.59 532.67 1016.84 57.70
2.24 300.78 460.48 21.00 1.01 345.80 560.03 28.27 2.76 387.08 665.46 35.54 2.13 432.58 776.32 42.81 2.63 479.03 891.45 50.08 2.52 535.10 1013.48 57.35
8.08 293.95 451.91 21.10 6.30 321.65 515.70 28.37 6.56 356.66 621.61 35.64 6.36 420.67 739.14 42.91 6.21 460.87 853.55 50.18 6.11 540.52 1009.46 57.45
5
6
7
8
the preceding and following 4m þ 2 type system within the homologous series.
Nitrogen substituted
R
4
189
In each case the first, second, third and forth entries are dipole moment, area, volume and polarizability values, respectively (Dipole moments in the order of 10230 C.m., area in the order of 10220 m2, volume in the order of 10230 m3, and polarizability in the order of 10230 m3).
formation, B –P, N –F, N – P type structures become less endothermic as R increases. Whereas B – F type structures possess the cryptoannulenic effect such that a 4m-type system is more endothermic than
References [1] M.J.S. Dewar, R.C. Dougherty, PMO Theory of Organic Chemistry, Plenum Press, New York, 1975. [2] I. Agranat, B.A. Hess Jr., L.J. Schaad, Pure Appl. Chem. 52 (1980) 1399. [3] J.L. Bergan, B.N. Cyvin, S.J. Cyvin, Acta Chim. Hung. 124 (1987) 299. [4] G. Ege, H. Vogler, Theor. Chim. Acta 35 (1974) 189. [5] E. Heilbronner, Helv. Chim. Acta 37 (1954) 921. [6] G. Derflinger, H. Sofer, Monatch. Chem. 99 (1968) 1866. [7] S. Kivelson, O.L. Chapman, Phys. Rev. B 28 (1983) 7326. [8] F.J. Zhang, S.J. Cyvin, B.N. Cyvin, Monatch. Chem. 121 (1990) 421. [9] P.R. Ashton, N.S. Isaac, F.H. Kohnke, A.M.Z. Slawin, C.M. Spencer, J.F. Stoddart, D.J. Williams, Angew. Chem. Int. Ed. Engl. 27 (1988) 966. [10] R.W. Alder, R.B. Sessions, J. Chem. Soc. Perkin Trans. 2 (1985) 1849. [11] R.O. Angus Jr., R.P. Johnson, J. Org. Chem. 53 (1988) 314. [12] L. Tu¨rker, Polycycl. Aromatic Compd 4 (1994) 191. [13] L. Tu¨rker, Polycycl. Aromatic Compd 8 (1996) 67. [14] L. Tu¨rker, Polycycl. Aromatic Compd 4 (1995) 231. [15] L. Tu¨rker, Polycycl. Aromatic Compd 8 (1996) 203. [16] L. Tu¨rker, J. Mol. Struct. (Theochem) 407 (1997) 217. [17] L. Tu¨rker, J. Mol. Struct. (Theochem) 454 (1998) 83. [18] I. Gutman, P.U. Biederman, V.I. Petrovic, I. Agranat, Polycycl. Aromatic Compd 8 (1996) 189. [19] S. Iijima, Nature 354 (1991) 56. [20] G. Overney, W. Zhong, D. Tomainek, Zeitschrift fur Physik D 27 (1993) 93. [21] M.J.S. Dewar, E.G. Zoebisch, E.F. Healey, J.J.P. Steward, J. Am. Chem. Soc. 107 (1985) 3902. [22] K.J. Miller, J. Am. Chem. Soc. 112 (1990) 8533.