1824
J. Phys. Chem. 1995, 99, 1824-1825
Infrared Observation of 2,3-Didehydrogenated Naphthalene (2d-Naphthyne) in Inert Gas Matrices at 4 K H. A. Weimer, B. J. McFarland, S. Li, and W. Weltner, Jr.* Department of Chemistry and Center for Chemical Physics, University of Florida, Gainesville, Florida 3261 I Received: September 23, 1994; In Final Form: January 3, 1 9 9 9
Infrared spectra of matrix-isolated 2,3-didehydrogenated naphthalene, C I O H ~have , been observed. CIO& was prepared by UV irradiating 2,3-naphthalene anhydride isolated in inert gas matrices at 4 K. Good agreement between theoretical calculations by Pauzat, Talbi, and Ellinger and the observed spectra was found.
Introduction Benzyne' and possibly its congeners naphthyne, anthracyne, etc., are of interest as reactive intermediates. Apparently, benzyne (0-didehydrobenzene) is the only member of this yne family whose infrared spectrum has been ~haracterized.~-' For the larger aromatic ring systems, the didehydro molecules are of interest because of possible relevance to the identification of infrared emission features in celestial objects correlating with polycyclic aromatic hydrocarbon (PAH) spectra.*-I0 In fact, the reason for publishing our experimental results at this time is the recent theoretical calculations of Pauzat, Talbi, and Ellinger (PTE)" of the infrared frequencies and intensities of several dehydrogenated naphthalenes, including 2,3-naphthyne. Here we present a comparison of those assignments with the frequencies obtained by photolyzing 2,3-naphthalene anhydride (NA) in neon, argon, and krypton matrices.
Experimental Section 2,3-Naphthalene anhydride was synthesized according to the procedure of Campbell and Grimmett.'2 The anhydride was vaporized at about 90 "C and cocondensed with neon (Matheson, 99.999%), argon (Airco, 99.999%), or krypton (Airco, 99.999%) onto a gold surface at 4 K. Absorption spectra were measured by reflection with a vacuum Fourier transform infrared spectrometer (Bruker IFS-113V). A liquid nitrogen cooled mercurycadmium-telluride (MCT) detector was used for the midinfrared region (400-4800 cm-' ) and a DTGS-polyethylene detector with a 3.5 pm Mylar beam splitter for the far-infrared (200-600 cm-I). A high-pressure mercury lamp (AH-6, water cooled) was used to irradiate the naphthalene anhydride sample.
GOO
500 400 Wavenumbers ( c m - I )
Figure 1. Absorption spectrum of 2,3-naphthalene anhydride (bands pointing down) in neon and argon matrices at 4 K. The starred bands in the difference spectrum after photolysis (upward pointing bands) are assigned to 2,3-didehydrogenated naphthalene.
co2 ,
Results Figures 1-3 show the infrared spectrum of NA in neon and argon matrices (bands projected down) and the difference spectrum after W photolysis, i.e., the emerging spectrum of 2,3-naphthyne (bands projected up). Irradiation leads to the production of the naphthyne, CO, and COz according to the reaction (The ultraviolet spectra of didehydrogenated naphthalenes, prepared by flash photolysis of the anhydrides, have been measured by Lohmann.I3) A similar procedure has been used with phthalic anhydride for the preparation and characterization of b e n ~ y n e . ~ < 'The ~ - ' starred ~ bands in the neon spectra in the figures are attributed to 2,3-naphthyne and are listed in Table @
Abstract published in Advance ACS Absrracrs, February 1, 1995.
1000 Wavenumberr ( c m - 1 )
I500
Figure 2. Absorption spectrum of 2,3-naphthalene anhydride (bands pointing down) in neon and argon matrices at 4 K. The starred bands in the difference spectrum after photolysis (upward pointing bands) are assigned to 2,3-didehydrogenated naphthalene. 0 II
a
;
o
II 0
+
+ co + con
1, along with the corresponding bands in argon and krypton matrices. Column 5 of that table contains the most intense of
0022-365419512099-1824$09.0010 0 1995 American Chemical Society
J. Phys. Chem., Vol. 99, No. 7, 1995 1825
Letters
3200
3000 Wavenumbers ( c m - 1 )
Figure 3. Absorption spectrum of 2,3-naphthalene anhydride (bands pointing down) in neon and argon matrices at 4 K. The starred bands in the difference spectrum after photolysis (upward pointing bands) are assigned to 2,3-didehydrogenated naphthalene. TABLE 1: Infrared Absorption (cm-l) of 23-Didehydrogenated Naphthalene in Matrices observed Ne 3098 3084
3069 1213.1 1018.3d 848.6 834.1 738.6 618.1 451.8 446.5
calculated"
re1 intb
Ar
8
3082 3078 3063
10 16 4 2
9 37 47 79 9 (92)
833 738 618 444
Kr
847.6 832.2 736.7 616.2
444
freq
int
assigntc
3090 3078 3065 1232 1010 869 843 739
13 19 21 23 17 24 74 51 54 22 92
r(CH) r(CH) r(CH) P(CH)/R(CC) R(CC)/P(CH) a(CCC) c(CH) t(CCC) a(CCC) t(CCC) a(CCC)
600 446 438
a From ref 7. Measured intensity in neon matrix (km/mol) relative to an assumed (calculated) value of 92 for the 446.5 cm-' band. r(CH), C-H stretching vibrations; R(C-C), C-C aromatic vibration: P(CH), C-H in-plane bending vibration; a(CCC), C-C-C bending vibrations; c(CH), C-H out-of-plane bending vibration; t(CCC), C-C-C outof-plane bending vibration. See text.
the bands calculated by FTE, Le., those having intensities calculated to be greater than 10 km/mol. A C-C-C bending vibration calculated to lie at 438 cm-I, and predicted to be the most intense band, is assigned here to the band at 446.5 cm-' in neon, and indeed, it is the most intense measured absorption. Assuming this band to have the calculated intensity of 92 km/ mol, intensities could be assigned to the other experimental bands by comparing their areas. These measured relative intensities are given in Table 1 in column 2 and are in fair agreement with the calculated ones in column 6. (It should be stressed here that, in general, computed intensities are not considered to be completely reliable and can easily be in error by a factor of 2.5J7J8It is also relevant that theoretical assignments of the vibrational frequencies of o-benzyne have undergone revision in recent Of course, strong CO and C02 bands were produced upon photolysis of the anhydride. T h e neon spectrum, not unexpectedly, is sharper than the argon spectrum. In general, the agreement is good, but there are some differences. The relatively strong unassigned band at 47 1.1 cm-' in neon does not appear in argon, and it is likely an artifact because of two strong background bands in that
neighborhood. The two bands at 834.1 and 848.6 cm-' in neon may possibly be overlapping at 833 cm-' in argon. A band is expected near 1010 cm-' according to PTE, but five progressively weaker bands in that region at 1072.3, 1054.0, 1037.6, 1018.3, and 981.6 cm-' are observed in neon. (The four strongest bands also appear in argon.) We have arbitrarily assigned the band at 1018.3 cm-' to the calculated 1010 cm-I band in Table 1, but that is only because of its proximity. It is tempting to assign some of these bands to the 2,3-naphthyne cation since the most intense band of the cation is calculated to lie at 1093 cm-I, and neighboring but weaker bands are predicted at 1034 and 1028 cm-'.I1 [By using their electron bombardment methodlo on the anhydride, Vala's group is presently preparing and measuring the spectrum of the 2,3naphthyne cation in an argon matrix.] These studies are being continued by measuring the infrared absorption of the 1,2-didehydrogenated naphthalene (1,2naphthyne) prepared in the same way. Also, because of the possibility of CO complexingI9 or reacting3 with the naphthynes during this preparation procedure, the effect of added CO will be studied and other avenues to the naphthynes sought.
Acknowledgment. We thank Professor J. Deyrup for his help with the anhydride synthesis, Professor M. Vala for his interest in this research, and a referee, Dr. L. Allamandola, for his helpful comments about the original manuscript. This research was supported by NSF Grant CHE-9114387 and also by the donors of the Petroleum Research Fund, administered by the American Chemical Society. References and Notes (1) Hoffmann. R. W. Dehvdrobenzene and Cvcloalkvnes; Academic Press: ' New York, 1967. (2) Nam. H. H.: Leroi, G. E. SDectrochim. Acta 1985,41A, 67; J. Mol. Struct.' 1987, 157, 301. (3) Simon, J. G. G.; Miinzel, N.; Schweig, A. Chem. Phys. Lett. 1990, 170, 187. (4) Scheiner, A. C.; Schaefer 111, H. F. Chem. Phys.Letr. 1991, 177, 471. ( 5 ) Radziszewski, J. G.; Hess, Jr., B. A,; Zahradnik, R. J. Am. Chem. SOC. 1992, 114, 52. (6) Liu, R.; Zhou, X.; Pulay, P. J. Phys. Chem. 1992, 96, 8336. (7) Bludskg, 0.;Pirko, V.; Kobayoshi, R.; Jorgensen, P. Chem. Phys. Lett. 1994, 228, 568. (8) Hudgins, D. M.; Sandford, S. A,; Allamandola, L. J. J. Phys. Chem. 1994, 98, 4243 and references therein. (9) Leger, A.; d'Hendecourt, L.; Joblin, C. Adv. Space Res. 1993, 13, 473 and references therein. (10) Szczepanski, J.; Vala, M.; Talbi, D.; Parisel, 0.; Ellinger, Y. J. Chem. Phys. 1993, 96, 4494 and references therein. (1 1) Pauzat, F.; Talbi, D.; Ellinger, Y. Asrron. Astrophys., submitted. (12) Campbell, A. D.; Grimmett, M. R. Aust. J. Chem. 1963, 16, 854. (13) Lohmann, J. J. Chem. SOC., Faraday Trans. 1 1972, 68, 814. (14) Dunkin, I. R.; MacDonald, J. G. J. Chem. Soc., Chem. Commun. 1979, 772. (15) Chapman, 0. L.; Mattes, K.; McIntosh, C. L.; Pacansky, J.; Calder, G. V.; Orr, G. J. Am. Chem. Soc. 1973, 95, 6134. (16) Chapman, 0. L.; Chang, C.-C.; Kolc, J.; Rosenquist, N. R.; Tomioka, H. J. Am. Chem. Soc. 1975, 97, 6586. (17) Pauzat, F.; Talbi, D.; Miller, M. D.; DeFrees, D. J.; Ellinger, Y. J. Phys. Chem. 1992, 96, 7882. (18) Person, W. B.; Szczepaniak, K.; Szczesniak, M.; Del Bene, J. E. In Recent Experimental and Computational Advances in Molecular Svectroscovv: Fausto. R.. Ed.. Kluwer Academic Publishers: Dordrecht. (993; pp 1'41-169. (19) Hobza, P.; Zahradnik, R.; Hess, Jr., B. A,; Radziszewski, J. G. Theor. Chim. Acta 1994, 88, 233 JP942576E
