Fluorescence-dip infrared spectroscopy of tropolone and tropolone-OD

Abstract

Fluorescence-dip infrared spectroscopy ͑FDIRS͒ is employed to record the infrared spectra of the isolated, jet-cooled tropolone molecule ͑TrOH͒ and its singly deuterated isotopomer TrOD in the O-H and C-H stretch regions. The ability of the method to monitor a single ground-state level enables the acquisition of spectra out of the lower and upper levels of the zero-point tunneling doublet free from interference from one another. The high power of the optical parametric oscillator used for infrared generation produces FDIR spectra with good signal-to-noise despite the weak intensity of the C-H and O-H stretch transitions in tropolone. The expectation that both spectra will exhibit two OH stretch transitions separated by the OH(vϭ1) tunneling splitting is only partially verified in the present study. The spectra of TrOH are compared with those from deuterated tropolone ͑TrOD͒ to assign transitions due to C-H and O-H, which are in close proximity in TrOH. The appearance of the spectra out of lower ͑a 1 symmetry͒ and upper ͑b 2 symmetry͒ tunneling levels are surprisingly similar. Two sharp transitions at 3134.9 cm Ϫ1 ͑out of the a 1 tunneling level͒ and 3133.9 cm Ϫ1 ͑out of the b 2 tunneling level͒ are separated by the ground-state tunneling splitting ͑0.99 cm Ϫ1 ͒, and thereby terminate in the same upper state tunneling level. Their similar intensities relative to the C-H stretch transitions indicate that the y-and z-polarized transitions are of comparable intensity, as predicted by ab initio calculations. The corresponding transitions to the other member of the upper state tunneling doublet are not clearly assigned by the present study, but the broad absorptions centered about 12 cm Ϫ1 below the assigned transitions are suggested as the most likely possibility for the missing transitions.

Computational study of keto–enol equilibria of tropolone in gas and aqueous solution phase

“…Differences in bond length are rarely greater than Table 1 Gas phase absolute electronic energy in atomic units (hartrees), and relative energies (kcal mol À1 ) for tropolone (species (1) and (2)) and 3,5-and 3,6-cycloheptadiene-1,2-dione (molecules (3) and (4), respectively), evaluated at HF and B3LYP levels of theory, with 6-311++G ** and aug-cc-pVDZ basis sets, as well as with the G3 method Table 2 Absolute and relative electronic energy in atomic units and kcal mol À1 , respectively, at HF and B3LYP levels of theory for the four molecules in aqueous solution using the Onsager dipole and polarizable continuum solvent reaction field models in combination with 6-311++G ** and augcc-pVDZ basis sets 0.02 Å while bond angles, for the most part, agreed to within a degree. The largest difference between aqueous and gas phase bond angles was found for: A (3,4,5) in (1) with value +3.3°, A (12,14,15) in (2) is À0.9°, A (2,13,11) in (3) is +1.2°, and A (5,7,9) in (4) is +1.5°. The B3LYP gas phase optimized geometry of tropolone agrees very well with previous B3LYP/6-31+G * [15] and MP2/6-31G ** [14] calculations.…”

“…The largest difference between aqueous and gas phase bond angles was found for: A (3,4,5) in (1) with value +3.3°, A (12,14,15) in (2) is À0.9°, A (2,13,11) in (3) is +1.2°, and A (5,7,9) in (4) is +1.5°. The B3LYP gas phase optimized geometry of tropolone agrees very well with previous B3LYP/6-31+G * [15] and MP2/6-31G ** [14] calculations. The aromatic character of the two tropolone conformers (1) and (2), as exemplified by p-bonding above and below the molecular plane, explains the C s point group symmetry.…”

“…Another example of a molecule that is of widespread interest is provided by tropolone [10] (2-hydroxy-2,4,6-cycloheptatrien-1-one), a seven-membered cyclic analogue of hydroxycyclopropenone. This interest [11][12][13][14][15][16][17][18][19][20][21][22] has flourished largely due to the experimental detection of vibrational state-specific spectroscopic tunnelling doublets in its ultraviolet and infrared spectra, which in turn has spawned research into multi-dimensional tunneling dynamics. Other important motivations for the study of tropolone and its derivatives are due to the fact that they are found throughout nature, and a few investigations which have been carried out on these compounds have shown that they exhibit anti-tumour activities [23], phytogrowth inhibitory behaviour [24], and strong insecticidal properties [25].…”

Coherent Proton Tunneling in Hydrogen Bonds of Isolated Molecules: Malonaldehyde and Tropolone

“…1.5 shows peaks appear in the region. Vibrational assignments [34,86] were proposed on the basis of (i) gas phase IR spectra at lower frequencies, (ii) moderately high level MO computations, (iii) two-laser fluorescence dip IR spectra (FDIRS) of jet-cooled TRN(OH) and TRN(OD) by Frost et al [33], (iv) the IR spectra of Ne matrix-isolated samples [24], and (v) the results of independent theoretical computations of the spectral doublet for the OH stretching fundamental. The weak OH stretching fundamental assigned in Fig.…”

“…MA has 21 and TRN has 39 internal coordinates available for coupling into their tunneling processes. MA, with a developing experimental base [9][10][11][12][13][14][15][16][17][18][19][20][21], holds a computational edge over TRN which currently stands alone in its size group for its catalog of spectroscopic tunneling structures [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]. With 15 atoms TRN is reasonably expected to model elements of the intramolecular dynamical behavior occurring in much larger molecules, and it is amenable to high level experimental and theoretical studies.…”