Kinetics of Diels-Alder Adducts Formation Between Cyclopentadienyl Model Compounds and 1,4-Naphthoquinone

When one takes into account Diels-Alder reactions of cyclopentadiene derivatives with dienophiles, the concurrent reaction of dimerization of the diene has to be considered. Furthermore, it is known that Diel-Alder adducts can undergo dis- 

In order to avoid some difficulties during the treatment of the experimental data (change of the kinetic order when the conversion increases difficulties of preparing a pure adduct between (V,f) and NQ), we have followed the approach of Wasser-man72), who deduced the value of k2 from Keq = ki/k2 (see Experimental). 

The values of k(, k2 and Keq obtained for the reactions of (V,f) and also (VI, a) with NQ, respectively at 62 and 80 °C, are listed in Table 22. These data show that NQ reacts faster with (V,f) than (VI,a) (the second reaction occurs at an appreciable rate only above 80 °C), but the latter adduct is more stable. 

The modification of polymers by means of Diels-Alder reactions has been previously described in the case of 1,3,5-hexatriene, 1,3,5-heptatriene and 2,4,6-octatriene homopolymers80. Despite the trans-tram-1,3-diene structure of the repeat units of 1,6-polytrienes, which is known to react with dienophiles at a rate five times that of cis-trans dienes, the reactions were largely incomplete even after long periods of time when they were carried out at moderate temperature with strong dienophiles. 

We have attempted to verify the indications emerging from the kinetic investigations carried out on model compounds (V,f) and (VI,a) also in the case of the corresponding EPTMs. 

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