1.3- Cyclooctadien

Conjugated dienes are those m which two carbon-carbon double bond units are con nected to each other by a single bond 1 3 Pentadiene and 1 3 cyclooctadiene contain conjugated double bonds... 

FIGURE 13 38 The ir ir transition in as trans 1 3 cyclooctadiene involves exci tation of an electron from the highest occupied molec ular orbital (HOMO) to the lowest unoccupied molecu lar orbital (LUMO)... 

HOMO-LUMO energy difference in ethylene is greater than that of cis trans 1 3 cyclooctadiene... 

Figure 13.37 shows the UV spectrum of the conjugated diene cis,trans-, 3-cyc o-octadiene, measured in ethanol as the solvent. As is typical of most UV spectra, the absorption is rather broad and is often spoken of as a band rather than a peak. The wavelength at an absorption maximum is refened to as the X ax of the band. There is only one band in the UV spectrum of 1,3-cyclooctadiene its X ax is 230 ran. In addition to UV-VIS bands are characterized by their- absorbance (A), which is a measure of how much of the radiation that passes through the sfflnple is absorbed. To correct for concentration and path length effects, absorbance is converted to molar absorptivity (e) by dividing it by the concentration c in moles per liter and the path length I in centimeters. 

The enamino ketone 5,5-dimethyl-l-pyrrolidinocyclohex-l-en-3-one (49) on treatment with dimethyl acetylenedicarboxylate and subsequent hydrolysis yielded 2,3-dicarbomethoxy-7,7-dimethyl- 1-hydroxy-5-oxo-1,3-cyclooctadiene (79). 

Is cyclooctatetraene aromatic To tell, compare the first and second hydrogenation energies, leading to 1,3,5-cyclooctatriene and then to 1,3-cyclooctadiene. (The energy for hydrogen is provided at left.)... 

A recent study of Murov and co-workers<106) indicates that the activation energies for isomerization are not the controlling factors. Thus the fluorescence of naphthalene is quenched (5 x 108M-1sec-1) by cis-trans-1,3-cyclooctadiene with isomerization to form cis-cis-1,3-cyclooctadiene. However, the compound bicyclo[4,2.0]oct-7-ene is not formed despite the low activation energy for this process ... 

Time, hr Bicyclo[4.2.0]-oct-7-ene, mole % cis,trans-1,3-Cyclooctadiene, mole % cis,cis-1,4-Cyclooctadiene, mole %... 

In many cases the transformations may be more complex than indicated by Eqs. (9.89)-(9.100). An example of this is the photochemistry of cis,cis-1,3-cyclooctadiene [Eq. (9.94)].<169) A close examination of this reaction indicates that bicyclo[4.2.0]oct-7-ene is formed but in low relative yields during the initial reaction (see Table 9.9). In addition, the cis,trans-1,3-cyclooctadiene is formed and then consumed as the reaction proceeds. Fonken showed that the bicyclooctene initially formed, however, was not from thermal isomerization of the cis,trans-diene. Still a third reaction was the 1,3 sigmatropic hydrogen shift to form the cis, cis-1,4-cyclooctadiene ... 

Like the [3.2.2]-peroxide, the parent system 23 could be prepared in two ways, either from 1,3-cyclooctadiene 28 345 or from 1,3,5-cyclooctatriene 31 a> (Eq. 18). 

In 1968, while investigating the efficacy of bis(rj-cyclopentadienyl)-diphenyltitanium as a catalyst for the isomerization of 1,5-cyclooctadiene to 1,3-cyclooctadiene, Hagihara and co-workers found that the presence of CO inhibited the isomerization. Under the reaction conditions imposed, Cp2Ti(CO)2 (1) and benzophenone were isolated. Furthermore, 1 showed poor catalytic activity for this isomerization (34). 

That the sequence shown in Scheme 3 is not the only pathway available for H—NiY formation is indicated by the isolation of 1,3-cyclooctadiene from the reaction products of the dimerization of propene with the n-cyclooctenylnickel system (25) (80) it seems reasonable that the H—NiY species 22 in this case is at least in part formed through direct elimination from 25 without prior monomer insertion into the Ni—C—bond [Eq. (6)] ... 

Further examples which show that the direction of Ni—C addition to propene can be changed from Ni — C2 to Ni — Cj by introducing P(i-C3H7)3 are to be found in the codimerizations of ethylene with propene (4, 12, 29) and of 1,3-cyclooctadiene with propene (4, 79). The last example is particularly informative, for in this case no ambiguity as to the assignment of the products to Ni - C4 or Ni - C2 type addition exists. 

The GED results obtained for 1,3-cyclooctadiene should be regarded with caution, as the data in Table 7 refer to a 25-year-old study, where it was assumed that only one conformer is present. The structure of 1,3-cyclooctadiene should therefore be reinvestigated. 

Some typical results are shown in Table 2. The table shows that oxidation of conjugated dienes such as isoprene, piperylene (1,3-pentadiene), cyclopentadiene and 1,3-cyclohexadiene with a carbon anode in methanol or in acetic acid containing tetraethylammonium p-toluenesulfonate (EtjNOTs) as the supporting electrolyte yields mainly 1,4-addition products2. 1,3-Cyclooctadiene yields a considerable amount of the allylically substituted product. 

Towards the end of this section it may be worthwhile to point out some new reactions with high-valent metals and TBHP. The first is a pyridinium dichromate PDC-TBHP system134. Nonsubstituted or alkyl-substituted conjugated dienes, such as 1,3-cyclooctadiene (87) and others (also linear dienes), yield keto allyl peroxides 88 (equation 18), whereas phenyl-substituted dienes such as 1,4-diphenylbutadiene (89) gave diketo compounds, 90 (equation 19). In further research into a GIF-type system135 with iron and TBHP, limonene gave a mixture of products with carvone as the major product. The mechanism is thought to proceed initially by formation of a Fe(V)-carbon... 

By the end of the 1970s, PdCl2(PPh3)2 was being used to hydrogenate 1,5-cy-clooctadiene [10]. The substrate isomerization to 1,3-cyclooctadiene preceded its... 

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