2-Methyl-l-heptene

S)-4-Methyl-1 -hexene (12), (+) (S)-4-methyl-2-hexene, and ( + )(S)-5-methyl-l-heptene (12) were synthesized and subjected to hydroformylation under a relatively high carbon monoxide pressure. The main product in all instances was the result of formylation of the terminal carbon atom on or next to the double bond of the starting olefin. The optical yields of these products were about 94% (Table I). 

The polymers of the optically active and racemic 4-methyl-1-hexene and the poly-(S)-5-methyl-l-heptene have isotactic structure (115) the same structure seems probable also in the case of the other polymers prepared till now from optically active or racemic a-olefins. 

The X ray spectra of the optically active and optically inactive polymers seem identical in the case of poly-4-methyl-l-hexene but different in the case of poly-5-methyl-l-heptene and poly-3-methyl-1-pentene (80,96). 

I. R. spectra of polymers of optically active and racemic monomers (12) having similar stereoregularity are identical in the case of poly-5-methyl-l-heptene, but slightly different in the case of poly-3-methyl-l-pentene and poly-4-methyl- 1-hexene. A very characteristic crystallinity band has been found in the I. R. spectrum of poly-5-methyl-l-heptene at 12.06 fi bands which seem connected with stereoregularity have been found in the I. R, spectrum of poly-4-methyl-l-hexene at 10.06 fi the nature of these bands has been proved when preparing a practically atactic sample by hydrogenation of poly-4-methyl-l-hexyne (24). 

The optical activity has been evaluated in some cases also in the solid state (112), and for the poly-(S)-5-methyl-l-heptene it appears of the same order of magnitude as in the liquid state and in solution (110). 

The failure in separating in fractions possessing optical activity of opposite sign the stereoregular polymers of racemic 5-methyl-l-heptene, polymerized in the presence of the same catalyst as that used to prepare polymers from racemic 3-methyl-l-pentene and 4-methyl-1-hexene (75), might be an indication that, in order to obtain prevailingly (R) and (S) separable polymers instead of random copolymers from racemic vinyl monomers, the asymmetric carbon atom of the monomer must be in a or in / position with respect to the double bond. 

Considering the polymers in which the side chain asymmetric carbon atom is in the y-position with respect to the main chain, a remarkable difference in molar rotation has been found between the monomeric units of the polymers and the model compounds in the case of poly-(S)-5-methyl-l-heptene but not in the case of poly-[(S)-2-methyl-butyl]-vinyl-ether or in the case of poly-(S) l.3-dimethyl-butyl methacrylate. The discrepancy might be related both to conformational and to electronic (113 a) factors. 

In these isotactic polymers, the optical purity of the monomer affected the optical activity via the relationship to the excess helical sense of the polymer (Figure l).47 In the case of isotactic poly[(5)-4-methyl-1-hexene] (2) and poly[(A)-3,7-dimethyTl-octene] (3), an increase in the optical purity of the monomers resulted in an increase in the optical activity of the polymers in a nonlinear fashion the optical activity of the polymers leveled off when the optical purity of the monomer reached ca. 80%. In contrast, in the case of isotactic poly[(5)-5-methyl-l-heptene] (4), the... 

Figure 4-21. Molar optical rotation per monomeric unit [< )] as a function of optical purity % of the monomer for poly[(S)-4-methyl-l-hexene] (top curve) poly[(S)-5-methyl-l-heptene], and poly[(R)-3,7-dimethyl-l-octene] (bottom curve) (after P. Pino, F. Ciardelli, G. Montagnoli, and O. Pieroni).

See Aoetylmesilyl oxide. 5-Methyl-l-heptenic Acid 2-Isoamylacrylic acid, 1-iso-octenic acid)... 

Fig. 2. Molar optical rotation [(0] f) ) vs polymerized monomer optical purity of isotactic vinyl polymers having the asymmetric carbon atom in the 7 position to the main chain. -O- poly-[(/J)-o -phenylethyl]-methacrylate -C- poly-(+)-menthylmethacrylate poly-(5 )-5-methyl-l-heptene poly-[(5 )-2-methylbutyl]-vinyl ether.

In other optically active polymers, as well as in some polymers from achiral monomers, chiral structures, characterized by all isomorphous helical chains in the unit cell, have been found. For instance, in isotactic poly(5-methyl-l-hexene) [94], isotactic poly(ubutylacrylate) [95], and optically active isotactic poly((S)-5-methyl-l-heptene) [94b,c], chiral pseudo-hexagonal or tetragonal packing with isomorphous 3/1 or 4/1 helical chains have been found. 

LiAIHa/TiCI 4/monomer Poly[(5)( -l-)5-methyl-l-heptene] Benzene 30-40 - 78.1 - Ill 6.25 8.88 (MC) Carbon tetrachloride 25 ... 

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