Chemical properties of alkadienes

Nomenclature of alkadienes
According to IUPAC rules, the main chain of an alkadiene molecule must include both double bonds. The numbering of carbon atoms in the chain is carried out so that the double bonds receive the lowest numbers. The names of alkadienes are derived from the names of the corresponding alkanes (with the same number of carbon atoms) with the addition of the ending - diene. Types of isomerism of alkadienes: Structural isomerism:
1) isomerism of the position of conjugated double bonds;
2) isomerism of the carbon skeleton;
3) interclass (isomeric to alkynes)
Chemical properties of alkadienes
For conjugated dienes, addition reactions are characteristic (reactions 1, 2). The presence of a conjugated system of p-electrons leads to the peculiarities of addition reactions. Conjugated dienes are capable of attaching not only to double bonds (C 1 and C 2, C 3 and C 4), but also to terminal (C 1 and C 4) carbon atoms by forming a double bond between C 2 and C 3. The ratio of the 1,2- and 1,4-addition products depends on the temperature at which the experiment was carried out and on the polarity of the solvent used.
Reduction (reaction 3) with the help is called reduction with hydrogen at the time of isolation (hydrogen is released when sodium and alcohol react). Alkenes are not reduced under such conditions; this is a distinctive property of conjugated dienes. Polymerization (reaction 4) is the most important property of conjugated dienes, which occurs under the action of various catalysts (AlCl 3, TiCl 4 + (C 2 H 5) 3 Al) or light. With the use of certain catalysts, a polymerization product with a certain chain configuration can be obtained. The cis configuration is of natural rubber. Macromolecules of natural rubber have a spiral chain structure due to the fact that the isoprene units are bent, which creates spatial obstacles to the ordered arrangement of the chains. In rubber, long molecules are twisted and entangled with each other in spirals. When the rubber is stretched, the spirals stretch, and when the stress is released, they twist again. Another polymer of isoprene, gutta-percha (trans configuration), also exists in nature. Gutta-percha has a rod-like chain structure due to the straightening of isoprene links (chains with a trans-configuration of double bonds can be located one along the other); therefore, gutta-percha is a hard but brittle polymer. Few countries have natural rubber and therefore it is being replaced by synthetic rubbers from divinyl, as well as from isoprene.