Dipole Moments of Tropolone and Related Compounds

Abstract

The dipole moments of tropolone (cycloheptatriene-2,4,6-ol-2-one-1) and related compounds were measured in benzene solution. The values obtained are:— tropolone, 3.71 D (25°) and 3.64 D (35°) ; tribromotropolone (3,5,7-tribromo-), 1.84D(25°); hinokitiol(4-isopropylcycloheptatriene-2,4,6-ol-2-one-1), 4.04 D (33°); α-monobromohinokitiol (7-bromo-), 4.32 D (33°); α-dibromohinokitiol (3,7-dibromo-), 4.27 D (33°); β-dibromohinokitiol (5,7-dibromo-), 3.14 D (20°); α-mononitrohinokitiol (3- or 7-nitro-), 6.19 D (25°); dinitrohinokitiol (3,5- or 3,7-dinitro-), 4.63 D (20°). The high dipole moments of tropolone and hinokitiol were explained adequately by taking into consideration the contribution of various resonance structures with a formal positive charge at the ring C-atoms. The resonance was supposed to give a certain amount of double bond character to each bond in the ring, causing plane cycloheptatrienolone ring. The position of substituents in the substituted tropolone and hinokitiols were determined and are given immediately after each name of these compounds in parentheses.

Tropones and Tropolones

“…A number of derivatives have been successfully oriented by comparison of their dipole moments with values calculated for the likely isomers (193,196,198,200).…”

“…Comparison of the value for tropone with that for cycloheptanone (3. (193,198) 3.64 (193,198) 3.53 (201) Tropolone derivative: (193,197,198) 3 (128) has been made (201). It has been pointed out (162, footnote 92) that this neglects the effect of conjugation, and the value (4.00 D) (29) for 3,5-dimethylcyclo-2-hexen-l-one has been quoted in this connection.…”

“…On this basis, and using for substituents the moments they have in corresponding benzene derivatives, it has been possible to calculate theoretical values in CCCXVIII CCCXIX fair agreement with the observed data. Such calculations have been successfully used to assign structures to a number of halogen derivatives of previously unknown orientation and to confirm the orientation of others (193,196,198,199,200,201). The assignments have subsequently been verified by chemical methods (see, e.g., 275).…”

Tetsuo Nozoe (1902−1996)

“…Based on his firm belief that the troponoids (and azulenoids described in the next section) were aromatic compounds, Nozoe felt it necessary to expand the research on these compounds from organic chemistry into physicochemistry, in order to elucidate the fine details of their structure. The following areas were all investigated in collaboration using material provided by Nozoe: Determination of dipole moments, [40,52,53,60,110,111,167] magnetic susceptibilities, [118,135] ionization potentials [154] and dissociation constants, [61,189] quadrupole resonance, near infrared, Raman, and UV absorption spectroscopy, metal complexation, [183] electron diffraction and X-ray crystallography studies, molecular orbital calculations, mass spectrometry, [198] and polarography. [136,132,155] Through the meetings held from time to time, a deeper understanding of the physical properties of the troponoids and azulenoids was achieved, and, as a result, these compounds gained a firm footing in aromatic chemistry.…”