5-Fluoro- and 5-methyl-1,3-didehydrobenzene—a matrix isolation study

Abstract

The UV photolysis of [2.2]metaparacyclophanediones 4b and 4c leads to α-cleavage and formation of CO, p-xylylene 5, and m-benzynes 2b and c with a fluorine or methyl substituent in the 5-position, respectively. The IR spectra of 2b and 2c were assigned by comparison with that of the parent m-benzyne 2a and with spectra calculated at the BLYP/6-311G(d,p) level of theory. Both band positions and intensities of the experimental spectra are in excellent agreement with the DFT calculations. This method thus provides a reliable tool for the investigation of ground state properties of m-benzynes. The benzynes 2 exhibit a very strong IR absorption at 545 ± 2 cm^–1 which is almost not affected by the substituents and therefore can be used to identify m-benzynes in product mixtures.

References

1. C. Grundmann, ‘Arene und Arine’, in Houben Weyl, Methoden der Organischen Chemie, Vol. 5, Thieme, Stuttgart, 1981, pp. 613–648.
2. K. C. Nicolaou and W. M. Dai, Angew. Chem., 1991, 103, 1453; Angew. Chem., Int. Ed. Engl., 1991, 30, 1387.
3. R. H. Levin, ‘Arynes’, in Reactive Intermediates, Vol. 1, ed. M. Jones Jr. and R. A. Moss, Wiley, 1978, pp. 1–26.
4. W. Sander, Acc. Chem. Res., 1999, 32, 669.
5. S. G. Wierschke, J. J. Nash and R. R. Squires, J. Am. Chem. Soc., 1993, 115, 11 958.
6. P. G. Wenthold, J. A. Paulino and R. R. Squires, J. Am. Chem. Soc., 1991, 113, 7414.
7. P. G. Wenthold, J. Hu and R. R. Squires, J. Am. Chem. Soc., 1994, 116, 6961.
8. P. G. Wenthold and R. R. Squires, J. Am. Chem. Soc., 1994, 116, 6401.
9. P. G. Wenthold, J. Hu and R. R. Squires, J. Am. Chem. Soc., 1996, 118, 11 865.
10. J. J. Nash and R. R. Squires, J. Am. Chem. Soc., 1996, 118, 11 872.
11. D. Schröder, N. Goldberg, W. Zummack, H. Schwarz, J. C. Poutsma and R. R. Squires, Int. J. Mass Spectrom. Ion Processes, 1997, 165/166, 71.
12. P. G. Wenthold, R. R. Squires and W. C. Lineberger, J. Am. Chem. Soc., 1998, 120, 5279.
13. E. Kraka, D. Cremer, G. Bucher, H. Wandel and W. Sander, Chem. Phys. Lett., 1997, 268, 313.
14. K. K. Thoen and H. I. Kenttaemaa, J. Am. Chem. Soc., 1999, 121, 800.
15. R. Marquardt, W. Sander and E. Kraka, Angew. Chem., 1996, 108, 825; Angew. Chem., Int. Ed. Engl., 1996, 35, 746.
16. G. Bucher, W. Sander, E. Kraka and D. Cremer, Angew. Chem., 1992, 104, 1225; Angew. Chem., Int. Ed. Engl., 1992, 31, 1230.
17. W. Sander, G. Bucher, H. Wandel, E. Kraka, D. Cremer and W. S. Sheldrick, J. Am. Chem. Soc., 1997, 119, 10 660.
18. D. C. Smith, E. E. Ferguson, R. L. Hudson and J. R. Nielsen, J. Chem. Phys., 1953, 21, 1475.
19. S. E. Worthington and C. J. Cramer, J. Phys. Org. Chem., 1997, 10, 755.
20. C. J. Cramer, J. J. Nash and R. R. Squires, Chem. Phys. Lett., 1997, 277, 311.
21. M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez and J. A. Pople, GAUSSIAN94, Revision B.3, Gaussian, Inc., 1995.
22. C. Lee, W. Yang and R. G. Parr, Phys. Rev. B: Condens. Matter, 1988, 37, 785.
23. A. Becke, J. Chem. Phys., 1993, 98, 5648.
24. R. Krishnan, J. S. Binkley, R. Seeger and J. A. Pople, J. Chem. Phys., 1980, 72, 650.
25. V. Boekelheide, P. H. Anderson and T. A. Hylton, J. Am. Chem. Soc., 1974, 96, 1558.
26. T.-L. Chan, T. C. W. Mak and J. Trotter, J. Chem. Soc., Perkin Trans. 2, 1980, 672.