1,3,5-Hexatrienes theoretical studies

Theoretical studies have indicated that m-bcnzync is monocyclic with a C(l)-C(3) distance of 2.0 A whereas in tetrafluoro-w-benzyne the increased eclipsing strain between fluorine atoms stabilizes the bicyclo[3.1.0]hexatriene form with a C(l)-C(3) distance of 1.75 A.56 Computational studies coupled with gas-phase experimental studies show that appropriate substituents can be used to tune the reactivity of 1,3-arynes. Thus the presence of NH+ at C(5) makes (13) mildly carbocationic whereas the addition of OH at C(4) in (14) gives a highly reactive (bi)radical.57... 

Several theoretical studies have been devoted to the ground state structure of all-tra s-1,3,5-hexatriene and all-fratts-i,3,5,7-octatetraene . Tables 4 and 5 present the values of the CC bond lengths obtained in some selected theoretical calculations. 

High energy stable rotamers of hexatriene have also been theoretically studied . Two possible Cis/Trans isomers are possible with respect to the Cl=C2 bond (see Figure 2). For each of them, the rotation around the Cl—C3 and C2—C4 bonds can lead to s-trans and gauche conformations. The gauche-Trans-trans, trans-Cis-trans gauche-Cis-trans conformers have been found to be 3.0, 2.0 and 5.1 kcalmol above the most stable all-trans conformation, respectively. ... 

We will now discuss an application of the strategy described above to the radiationless decay and competitive photoproduct formation process in the cyclohexadiene (CHD)/hexatriene (HT) system. A theoretical study of the first singlet excited state (2Aj) of cZc-hexa-l,3,5-triene (cZc-HT)... 

Zilberg S, Haas Y. The photochemistry of 1,4-cyclohexadiene in solution and in the gas phase conical intersections and the origin of the helicopter-type motion of H-2 photo-generated in the isolated molecule. Phys Chem Chem Phys. 2002 4 34-42. Tamura H, Nanbu S, Nakamura H, Ishida T. A theoretical study of cyclohexadiene/ hexatriene photochemical interconversion multireference configuration interaction potential energy surfaces and transition probabilities for the radiationless decays. Chem Phys Lett. 2005 401 487-491. 

These compounds have been the subject of several theoretical [7,11,13,20)] and experimental[21] studies. Ward and Elliott [20] measured the dynamic y hyperpolarizability of butadiene and hexatriene in the vapour phase by means of the dc-SHG technique. Waite and Papadopoulos[7,ll] computed static y values, using a Mac Weeny type Coupled Hartree-Fock Perturbation Theory (CHFPT) in the CNDO approximation, and an extended basis set. Kurtz [15] evaluated by means of a finite perturbation technique at the MNDO level [17] and using the AMI [22] and PM3[23] parametrizations, the mean y values of a series of polyenes containing from 2 to 11 unit cells. At the ab initio level, Hurst et al. [13] and Chopra et al. [20] studied basis sets effects on and y. It appeared that diffuse orbitals must be included in the basis set in order to describe correctly the external part of the molecules which is the most sensitive to the electrical perturbation and to ensure the obtention of accurate values of the calculated properties. 

Theoretical and time-resolved spectroscopic studies of triene photochemistry The dynamics of relaxation of the excited singlet states of E- and Z-l,3,5-hexatriene (HT) have recently been studied in the gas phase and in solution. In the gas phase, population of the 21 / state of the Z-isomer by internal conversion from the spectroscopic 11B state has been estimated to occur with a lifetime Tig of about 20 fs, while the lifetime of the 21 / state has been determined to be T2A =730 fs47. The lifetime of the latter in ethanol solution has been determined by Fuss and coworkers to be T2a = 470 fs52. A similar 21A lifetime has been reported for -l,3,5-hexatriene in cyclohexane and acetonitrile solution by Ohta and coworkers48. 

There is no unity of opinion in the literature concerning a classification, i.e, whether to call these transformations aza-Claisen or aza-Cope rearrangements. It is accepted that the term aza-Claisen should be reserved only for those processes in which a carbon atom in the allyl vinyl ether system has been replaced by nitrogen357. Three different types of aliphatic 3-aza-Cope reactions which were studied theoretically are the rearrangements of 3-aza-l,5-hexadienes (610, equation 262), 3-azonia-l,5-hexadienes (611, equation 263) and 3-aza-l,2,5-hexatrienes (612, equation 264) (the latter is a ketenimine rearrangement )357. 

Theoretical and time-resolved spectroscopic studies of triene photochemistry The dynamics of relaxation of the excited singlet states of E- and Z-l,3,5-hexatriene... 

A theoretical investigation of the thermal rearrangements of l-hexen-5-yne, 1,2,5-hexatriene, and 2-methylenebicyclo[2.1.0]pentane has been reported providing a theoretical account of the pyrolysis reactions. The computed energy values are in agreement with experimental product distributions. The thermal C(2)-C(6)/ene cyclization of enyne-allenes has been reviewed. A computation study of the thermal rearrangements of l-ethynyl-2-methylcyclopropane has been reported. " ... 

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