Methylcyclopentadiene: hydrogen

The abovementioned materials can be mixed with one another. A series of other polymers and resins can also be added if the substances listed in 1 to 4 form the bulk of the material. Additional materials are PE, PP, low molecular weight polyolefins, polyterpenes (mixtures of aliphatic and cycloaliphatic hydrocarbons produced by polymerisation of terpene hydrocarbons), polyisobutylene, butyl rubber, dammar gum, glycerine and pentaerythritol esters of rosin acid and their hydration products, polyolefin resins, hydrated polycyclopentadiene resin (substance mixtures manufactured by thermal polymerization of a mixture mainly composed of di-cyclopentadiene with methylcyclopentadiene, isoprene and piperylene which is then hydrogenated). 

Since a [1,5] Slgmatropic rearrangement involves three electron pairs (two 7T bonds and one cr bond), the orbital-symmetry rules in Table 30.3 predict a suprafacial reaction. In fact, the fl,51 suprafacial shift of a hydrogen atom across two double bonds of a tt system is one of the most commonly observed of all slgmatropic rearrangements. For example, 5-methylcyclopentadiene rapidly rearranges at room temperature to 3rield a mixture of 1-methyl-, 2-methyl-, and 5-methyI-substituted products. 

It is interesting to note that this correlation allows one to estimate at least roughly the rates of 1,2-shifts of hydrogens in neutral compounds — methylcyclopentadienes (Sib) and (52i>) cf. Ref. — calculated values of AGh amount to 24.2 and 24.4 kcal/mole, experimental ones — to 22.5 and 23.7 kcal/mole, respectively 279,282)... 

It should be mentioned that fulvene can also yield benzene by ring expansion [116,121]. However, in contrast to methylcyclopentadiene, two hydrogen atoms are not ejected from the molecule as fulvene is an isomer of benzene. The barrier for... 

In contrast to the [l,5]-sigmatropic rearrangement of pentadienes, that of cy-clopentadienes proceeds at an appreciable rate at room temperature along a suprafacial pathway [36, 37]. For example, the enthalpy of activation for the hydrogen shift in 5-methylcyclopentadiene, is 20. kcal/mol [38] and that in cyclopentadiene itself, which has been proven isotopically to be intramolecular, is 24. kcal/mol [39]. The latter reaction is illustrated in Fig. 8.8, in which the circled hydrogen atom is depicted as migrating from Ci to C2. 

Methylcyclopentadiene readily undergoes reaction with metal carbonyls 47) and even 1,3-diphenylcyclopentadiene reacts with iron carbonyl 4S). A novel method for obtaining a ferrocene with one substituted ring, is the reaction of 1,3-diphenylcyclopentadiene with the dimer of cyclopentadienyl-iron dicarbonyl at 170° C to produce 1,3-diphenylferrocene in 15% yield. Other substituted cyclopentadienes which have been used are tetraphenyl-cyclopentadienone in the preparation of tetraphenyl(hydroxy)cyclopenta-dienylmanganese tricarbonyl 49) and indene in the preparation of the dimer of indenylmolybdenum tricarbonyl (50). A variety of substituted fulvenes have been used in the preparation of substituted cyclopentadienyl metal tricarbonyl compounds of Cr, Mo, and W (57, 52). This latter reaction proceeds best in the presence of a solvent, such as 1,2-dimethoxyethane, to permit easy abstraction of hydrogen. 

Methylcyclopentadiene undergoes homolytic bond cleavage of a C—H bond to form a radical that exhibits five resonance structures. Determine which hydrogen is abstracted and draw all five resonance stmctures of the resulting radical. 

Step la. The liquid-pha.se metalation reaction between methylcyclopentadiene (MCP) and sodium in a solvent of diethylene glycol dimethyl ether (diglyme) to produce sodium methylcyclopentadiene and hydrogen gas ... 

Fig. 4 Stress tensor analysis of the reactant in the 1,5-sigmatropic hydrogen shift reaction from 5-methylcyclopentadiene to 1-methylcyclopentadiene. The eigenvectors of the stress tensor at the heps of the two active C-H bonds are shown. The stress tensor was computed at the B3LYP/ 6-31 lG(d,p) level. Further details can be found in the paper of Guevara-Gareia et al. [32]...

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