Polyenes Tetraenes, Trienes

We will first discuss results corresponding to 1,3-butadiene. This molecule is the simplest of the series, so that several levels of calculation have been used, thus permitting one to establish the minimum requirements of the theoretical treatment. The extension to trienes, tetraenes and longer polyenes will be discussed in further subsections. 

Migration of the metal along the polyene chain in (l,l- 2-l,3,5-hexatriene)CoCp occurs with an activation energy of 25.6 kcalmoT 1 (equation 15)136b. This barrier is ca 5-8 kcal mol 1 lower than that for metal migration in (triene)- or (tetraene)Fe(CO)3 complexes (see Section IV.E.l.d). 

The construction of models emphasises all these stereoisomeric features also note that in a homologous sequence of cumulative polyenes, the presence of a chiral axis, or of geometric isomerism, alternates [i.e. diene (R/S), triene (E/Z), tetraene (R/S), etc.]... 

Among cyclic polyenes, cyclic dienes, trienes and tetraenes have been ring-open polymerised via the metathesis reaction. Representative of the cyclodienes most commonly used for polymerisation are 1,5-cyclooctadiene, norbornadiene (bicyclo[2.2.1]hept-2,5-diene) and dicyclopentadiene as mono-, bi- and tricyclic diolefins respectively. Cycloocta-1,5-diene metathesis polymerisation is another approach to the preparation of 1,4-polybutadiene ... 

HPLC analyses, after longer irradiation periods, have shown that the tetraene structures are increasingly destroyed upon exposure to photonic energy. The amount of degradation products with triene structure increases steadily. Comparable results have been seen with other polyene antibiotics (13). 

Ramamurthy and Liu [85] reported on the effect of chain length on the potential energy surfaces of triplet-sensitized isomerization of polyenes of retinal homologs. Thus dienes and trienes undergo unimolecular deactivation from the twisted triplet because the planar trans triplet and the twisted triplet are in equilibrium and are very close in energy. On the other hand, in tetraenes and higher polyenes, deactivation proceeds from the planar triplet states, which are much more stable than the twisted triplet states. 

Witting- and Horwitt, 1962). This was done by comparing diets which contain saturated fats and a minimum of added linoleic acid and diets adjusted to provide different larger amounts of unsaturated fatty acids (Table I). Peroxidizability of tissues was estimated by arbitrarily giving a value of 1, 2, 4, 8, and 8 to the relative peroxidizability of diene, triene, tetraene, pentaene, and hexaene, respectively. It had previously been noted that when little or no tocopherol was present in such diets, the rate of appearance of dystrophy was slowest on the coconut oil diet and most rapid on the cod liver oil diet (Century and Horwitt, 1960 Century et al., 1961). If no tocopherol was provided to diets equal in unsaturation in terms of iodine value, as supplied by monoene, diene, triene, and polyene in syn-... 

Compounds with more than one double or triple bond exist. If two double bonds are present, the compounds are called alkadienes or, more commonly, dienes. There are also trienes, tetraenes, and even polyenes (compounds with many double bonds, from the Greek poly, many). Polyenes are responsible for the color of carrots (/3-carotene, p. 76) and tomatoes (lycopene, p. 68). Compounds with more than one triple bond, or with double and triple bonds, are also known. 

Polyene structures such as diene, triene and tetraene disappear under UV irradiation [1416]. 

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