Trans-hexatriene

Fig. II. (a) Schematic representation of hydrocarbons adsorbed on the [111] plane of platinum. Intersections of the lines of triangular net denote positions of the centers of platinum atoms. (1) Cyclohexane (2) all-cis conformation of cij-l,3,5-hexatriene (3) transoid conformations of cis- and trans-1,3,5-hexatriene (S4). (b) Adsorption configurations of acetylene and ethylene found most probable according to LEED studies 141).

It is not possible to separate the photochemistry of 1,3-cyclohexadiene from that of 1,3,5-hexatriene, its major product, since the latter absorbs radiation in the same region of the spectrum and even more intensely to revert to 1,3-cyclohexadiene. The ir- - w absorption of 1,3,5-hexatriene shows considerable vibrational structure. The radiative lifetimes for the singlet states of both 1,3-cyclohexadiene and 1,3,5-hexatriene can be calculated to be less than 10 sec. The lowest triplet state of trans-1,3,5-hexatriene has been placed at 47 kcal./mole, and a second triplet state may lie at approximately 14 kcal./mole above that. These values were also obtained by direct singlet — triplet excitation. 

Ergosterol (E) and lumisterol (L) bear the same relation to precalciferol (P) and tachysterol (T) as 1,3-cyclohexadiene does to ds- and trans-1,3,5-hexatriene. The details of the photochemical processes in this system have been studied extensively by Havinga and his co-workers. Phosphorescence has not been observed from any of these compounds, while fluorescence has been recorded from E, L, and T. Havinga and Schlatmann have concluded that the photochemical transformations in... 

Dimethyl-1,3-butadiene 2-Methyl-l, 3-butadiene cb-1,3-Butadiene trans-1,3-Butadiene ci i-1,3-Pentadiene trans-1,3-Pentadiene cw-1,3,5-Hexatriene trans-1,3,5-Hexatriene... 

Fig. 6. Pi orbital interactions in the A -t- (B Q union to form cis and trans 1,3,5 hexatriene. See Fig. 5 for the construction of the group MO s spanning B and C. The symmetry labels are assigned with respect to a mirror plane (cis isomer) or a rotational axis (trans isomer)...

Toxaphene insecticide contains over 125 distinct Cio-cWoro-compounds, two components of which (a C,oHioCl7 compound and a CiqHj, Cl7 compound) appear to contribute mainly to the acute toxicity of the mixture. Crystal structure analysis establishes the C10H11CI7 component to be 2,2,5-emio,6-exo,8,9,l()-heptachloro-bornane. The crystal structure of the n-n photoproduct (6) obtained from the trans-1,3,5-hexatriene-p-benzoquinone Diels-Alder adduct, reveals the nature of the regiospecific [2 -I- 2] addition. ... 

The pole strength profiles obtained in the outer valence region of the 1,3-trans butadiene, 1,3,5-trans hexatriene and 1,3,5,7-trans octatetraene compounds relate also typically to that found (10) with low-gap hydrogen chains. They nicely reflect the competition for intensity between the main and the correlation i.e. satellite) bands in that region. In both cases, the less energetic (HOMO LUMO (10,12)... 

TABLE 4. Selected geometrical parameters" (A) of all-trans-hexatriene computed at several levels of calculation ... 

The only materials that have been examined for this purpose to date have been dienes and other polyenes.12 The major liability of these substances is their chemical reactivity. The finding that 1,3,5-trans-hexatriene quenches the phosphorescent emission from phenanthrene but does not have a significant effect on the fluorescent emission from 1,3,5,7-tetraphenylisobenzofuran indicates that chemical reactivity may not be too severe a problem, and that triplet quenchers may be effective tools for mechanistic work in ECL. Here too, further study is indicated. Unfortunately, or perhaps significantly, the compounds that produce the brightest emission on redox stimulation—1,3,4,7-tetra-phenylisobenzofuran and rubrene—have no detectable phosphorescence. Studies with sensitizers and quenchers have failed to produce any evidence regarding their triplet levels.12 Thus the mechanism of anni-hilative emission remains uncertain. 

The structures of both as- and trans-hexatriene have been determined by electron diffraction and two important features emerge. 

The most stable structure of trans-hexatriene is shown here. 

Figure 1. The derivative of transmitted current as a function of electron energy in ethylene, butadiene, els- and trans-hexatriene (from Ref. 24).

However, for butadiene and trans-hexatriene even the ordering of the excited states is still not established [53-55]. For cis-hexatriene the 2 A, excitation was observed below B2 [54] and the molecular geometry in the excited 2 A, state was... 

Namjesnik-Dejanovic K, Maurice PA (2001) Conformational and aggregate structures of sorbed natural organic matter on muscovite and hematite. Geochim Cosmochim Acta 65 1047-1057 Naves de Brito A, Svensson S, Correia N, Keane MP, Agren H, Sairanen OP, Kivimaki A, Aksela S (1992) X-ray induced electron yield spectrum of thin films of 1,3-trans-butadiene and 1,3,5-trans-hexatriene. J Electron Spect Rel Phen 59 293-305... 

V. Bulatov and I. Oref [/nt J. Chem. Kinet., 25, 1019-1027 (1993)] investigated the kinetics of the dimerization of trans-hexatriene in toluene solution. They indicate that a simplified form of the reaction network can be written as... 

Absorption Spectra of Trans-Butadiene and Trans-Hexatriene... 

Pig. 9. Experimental (a) and calculated (b) UV absorption spectra of the state of trans-hexatriene (reproduced from Ref. 137). 

Table 7 summarizes several predictions of mid-sized aromatic molecules from the study of Matsuzawa and Dixon. The p value for a molecule with the inversion symmetry operation (benzene) is zero from symmetry arguments. Note that there are sizeable deviations among the experimental observations of p and Y values, as they are also properties difficult to measure. Agreement in Table 7 should be considered reasonably good. Matsuzawa and Dixon have also compared their calculated y values of ethylene, frans-butadiene, and trans-hexatriene with those obtained from ab initio molecular orbital methods the results from their study show that B-LYP calculations are more accurate than those at the Hartree-Fock level and are of comparable accuracy to MP2 results. 

The different stereochemical features of thermal and photochemical [(,2 + 4] processes are nicely summarized in the reactions of I l6]-annulene, (Equation 6.31). The cyclizations occur at the tennini of the trans,cis,trans-hexatriene units of the [ 16]-annulene structure. 

Figure 2 Valence ADC[3] ionization spectra (full lines) of the (a) ethylene, (b) butadiene, (c) hexatriene and (d) octatetiaene compounds in their all-trans configuration (6-31G results). The dotted curves represent the partial contribution to the convoluted density of states arising from satellites with Tq < 0.40. ...

Suitable carbonyl compounds can thus be olefmated photochemicully with (diazobenzyl)diphenylphosphine oxide (7), the oxygen function being substituted by a diphenylmethylene group 18,20). Hence irradiation of 7 for a sufficient length of time in the presence of the corresponding unsaturated ketones affords the hepta-fulvene 27 23), the trans-1,3-butadiene 28 22 and the cross-conjugated hexatriene 2922> by direct olefination with the intermediate 9. 

The most stable conformation of both hexatriene and octatetraene is the al -s-trans one. Figure 2 represents these structures schematically. 

Vibrational frequencies of hexatriene and octatetraene have been reported by several authors21,24-26,36. The increase in the size of these molecules with respect to butadiene limits the use of highly accurate levels of calculation, so that a good choice of scaling factors is necessary to obtain useful results. Kofraneck and coworkers21 have shown that employing scale factors determined from vibrational data for trans structures alone does not give a balanced description of cis and trans structures. 

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