The electronic structure of cyclopropane, cyclopropene and diazirine an ab initio SCF-LCAO-MO study
Tóm tắt
The electronic structure of cyclopropane, cyclopropene and diazirine has been studied within the ab-initio SCF-LCAO-MO theoretical framework. The present results lead to a general bonding model for three-membered ring systems. Composition of the MO's, population analyses and electron density distribution diagrams were used to establish the nature of the bonding. The total electron density distributions in cyclopropane and in cyclopropene lead to a “bent bond” + “central hole” bonding model; however the bending angle is only ca. 5° and the central hole is not very deep with respect to the bonding regions (ca. 15% density depression). Special emphasis has been given to the nature of the σ bonds forming the ring system. It has been found that the ring bonding in cyclopropane and in cyclopropene is due principally to three MO's: (1) A low lying MO (3a
1) composed mainly of C(2s) AO's and contributing electron density principally inside the ring triangle. (2) Two MO's (6a
1 and 3b
2), which are the highest occupied MO's in cyclopropane and lie immediately below the π bond in cyclopropene, composed almost exclusively of C(2p) AO's in the ring plane and leading to electron density maxima outside the ring (density bending angle of ca. 20°) and to zero density in the centre of the ring. In the case of diazirine these MO's are appreciably perturbed by the presence of the nitrogen lone pairs. Three MO's contribute mainly to the description of the lone pairs, all of which also contribute to some extent to ring bonding. Furthermore, among these three MO's two lie below the π level, one of them being very low in energy. This is quite different from the usual picture. The present bonding picture has been compared to former semi-empirical models (especially the Coulson-Moffitt and the Walsh models). The strain, the “π” character and conjugative properties of the three-membered ring are discussed on the basis of its electronic structure. The special bonding features of this system confer on it a pseudo-π(ψ-π) character; the bonds making up the ring may be considered as ψ-π bonds.
Tài liệu tham khảo
Vogel, E.: Angew. Chem. 72, 4 (1960); Fortschr. chem. Forsch. 3, 130 (1955).
Advances in alicyclic chemistry: Edited by H. Hart and G. J. Karabatsos, Vol. 1. New York: Academic Press 1966.
Seebach, D.: Angew. Chem. 77, 119 (1965).
Coulson, C. A., and W. E. Moffitt: Philos. Mag. 40, 1 (1949).
-, and T. H. Goodwin: J. chem. Soc. (London) 1962, 1285; 1963, 3161.
Veillard, A., and D. del Re: Theoret. chim. Acta (Berl.) 2, 324 (1964).
Certain, P. R., V. S. Watts, and J. H. Goldstein: Theoret. chim. Acta (Berl.) 2, 324 (1964).
Randić, M., and Z. Mansić: Theoret. chim. Acta (Berl.) 3, 59 (1965).
Trinajstić, N., and M. Randić.: J. chem. Soc. (London) 1965, 5621.
Randić, M., and S. Borcić.: J. chem. Soc. (London) A 1967, 586.
Bernett, W. A.: J. chem. Educat. 44, 17 (1967).
Walsh, A. D.: Trans. Faraday Soc. 45, 179 (1949).
Walsh, A. D.: Nature 159, 165, 172 (1947).
Hoffmann, R.: J. chem. Physics 39, 1397 (1963).
Hoffmann, R.: J. chem. Physics 40, 2480 (1964).
Yonezawa, T., I. Morishima, M. Fuzü, and K. Fukui: Bull. chem. Soc. Japan 38, 1224 (1965).
—, K. Shimizu, and H. Kato: Bull. chem. Soc. Japan 40, 456 (1967).
Brown, R. D., and V. G. Khrisna: J. chem. Physics 45, 1482 (1966).
Dewar, M. J. S., and G. Klopman: J. Amer. chem. Soc. 89, 3089 (1967).
Baird, N. C., and M. J. S. Dewar: J. Amer. chem. Soc. 89, 3966 (1967).
Clark, O. T.: Theoret. chim. Acta (Berl.) 10, 11 (1968).
Roberts, J. D., A. Streitwieser, Jr., and C. Regan: J. Amer. chem. Soc. 74, 4579 (1952).
Hoffmann, R.: Tetrahedron 22, 539 (1966).
Frost, A. A., and R. A. Rouse: J. Amer. chem. Soc. 90, 1965 (1968).
Preuss, H., and G. Diercksen: Intern. J. quant. Chem. 1, 361 (1967).
Buenker, R. J., S. D. Peyerimhoff, and J. L. Whitten: Unpublished results (1967), cited in Krauss, M.: Technical Note 438, 130 (1967). Washington, D. C.: National Bureau of Standards. See also: Petke, J. D., and J. L. Whitten: J. Amer. chem. Soc. 90, 3338 (1968).
Huzinaga, S.: J. chem. Physics 42, 1293 (1965).
Clementi, E.: Chem. Reviews 68, 341 (1968) and references therein.
Lehn, J. M., B. Munsch, Ph. Millie, and A. Veillard: Theoret. chim. Acta (Berl.) 13, 313 (1969).
Interatomic Distances, Special publication No. 11, London: The Chemical Society 1958.
Kasai, P. H., R. J. Myers, J. R. Eggers, and K. B. Wiberg: J. chem. Physics 30, 512 (1959).
Pierce, L., and Sr. V. Dobyns: J. Amer. chem. Soc. 84, 2651 (1962).
Salez, C., and A. Veillard: Theoret. chim. Acta (Berl.) 11, 441 (1968).
Landolt-Börnstein: Zahlenwerte und Funktionen aus Physik-Chemie-Astronomie-Geophysik-Technik, I. Band: Atom- und Molekularphysik, 1. Teil: Atome-Ionen, 6th edition, p. 211. Berlin-Göttingen-Heidelberg: Springer 1950.
Lewis, G. N., and M. Randall: Thermodynamics, revised by K. S. Pitzer and L. Brewer, p. 672. New York: Mc. Graw Hill 1961.
Skinner, H. A., and G. Pilcher: Quart. Rev. 17, 264 (1963).
Turner, D. W.: In: Advances in physical organic chemistry. London-New York: Academic Press 4, 31, (1966).
Wiberg, K. B., W. J. Bartley, and F. P. Lossing: J. Amer. chem. Soc. 84, 3980 (1962).
Collin, J., and F. P. Lossing: J. Amer. chem. Soc. 81, 2064 (1959).
Paulett, G. S., and R. Ettinger: J. chem. Physics 39, 825 and 3534 (1963).
Clementi, E.: J. chem. Physics 46, 4737 (1967).
Mason, R., and G. B. Robertson: In: Advances in structure research by diffraction methods, edited by R. Brill, and R. Mason, 2, 35 (1966). Braunschweig: Vieweg. New York: Interscience.
Fritchie, Jr., C. J.: Acta crystallogr. 20, 27 (1966).
Hartman, A., and F. L. Hirshfeld: Acta crystallogr. 20, 80 (1966).
Riddell, F. G.: Quart. Rev. 21, 364 (1967).
Hoffmann, R.: Tetrahedron Letters 3819 (1965).
Pete, J. P.: Bull. Soc. chim. France 357 (1967).
Dauben, W. G., and G. H. Berezin: J. Amer. chem. Soc. 89, 3449 (1967).
Vogel, E.: Angew. Chem. 74, 829 (1962).
Schröter, G., J. F. M. Oth, and R. Merenyi: Angew. Chem. 77, 774 (1965).