Methyl substitution properties, table

OC-Methylstyrene. This compound is not a styrenic monomer in the strict sense. The methyl substitution on the side chain, rather than the aromatic ring, moderates its reactivity in polymerization. It is used as a specialty monomer in ABS resins, coatings, polyester resins, and hot-melt adhesives. As a copolymer in ABS and polystyrene, it increases the heat-distortion resistance of the product. In coatings and resins, it moderates reaction rates and improves clarity. Physical properties of a-methylstyrene [98-83-9] are shown in Table 12. 

The compounds Ln(C5H5)2Cl also have been made only with the lanthanides above samarium (772). These compounds are stable in the absence of air and moisture, sublime near 200 °C, are insoluble in non-polar solvents, and exhibit room temperature magnetic moments near the free ion values (772, 113). The chloride ion may be replaced by a variety of anions including methoxide, phenoxide, amide and carboxylate. Some of these derivatives are considerably more air-stable than the chloride — the phenoxide is reported to be stable for days in dry air. Despite their apparent stability, little is known about the physical properties of these materials. The methyl-substituted cyclopentadiene complexes are much more soluble in non-polar solvents than the unsubstituted species. Ebulliometric measurements on the bis(methylcyclopentadienyl)lanthanide(III) chlorides indicated the complexes are dimeric in non-coordinating solvents (772). A structmre analysis of the ytterbium member of this series has been completed (714). The crystal and molecular parameters of this and related complexes are compared in Table 5. 

If one of these structural conditions is not fulfilled, the molecule loses its unique properties. This is exemplified byTV-methyl substituted poly(p-phenylene terephthalamide) Its equilibrium rigidity (Table 10) is 20 times lower than that of the unsubstituted analog (Table 9) and approaches that of poly(m-phenylene isophthalamide). Probably, in this ase, the coplanar rrans-structure of the amide group is distorted by steric interactions of the pendant methyl group as in poly(alkyl iso-cyanate)s. 

As confirmation of an inert radical production mechanism, iodine compounds are particularly effective because of the production of I atoms. However, there are big deficiencies in our understanding of the details of anti-knock chemistry. This is illustrated by the large differences in antiknock effectiveness shown in MacKinven s measurements between substances with apparently very similar composition [27]. As shown in Table 7.3, some of the methyl substituted diphenyl oxalates are quite good antiknocks, with up to 1.1 times the molar effectiveness of NMA. But another is pro-knock. The mechanism responsible for this structure/property dependence is not known. More recently, high effectiveness has been reported for ashless materials related to dialkyl amino fulvenes [28-31], but no credible mechanisms have been published. No ashless anti-knocks have proved sufficiently cost-effective to be used commercially. 

The methyl-substituted phenylpyridine cyclometallated Ir(III) complexes, Ir(ptpy)2(bpy)+ and Ir(mppy)2(bpy)+, have been prepared and investigated [103,104]. The UV-visible absorption properties of these complexes are similar to that of the nonsubstituted ppy complex, displaying charge transfer transitions in the 325-468 nm spectral region. The emission spectra are also similar to that of the nonsubstituted complex. At room temperature in fluid solvents they display an emission maximum at 595 nm, but in rigid matrix at 77 K a dual structured emission with maxima centered at 527 and 550 nm are observed. The luminescence lifetimes are very close to those of Ir(ppy)2(bpy)+ (Table 2). 

A comparison of the attractant activity of 55 (5-OH, 7-OMe, tectochrysin), with that of 57 (5,7-di-OH, chrysin), and that of 77 (5-OH, 6,7-diOMe) with that of 54 (5,6,7-triOH) revealed that 7-0-methylation significantly increased activity. However, the 7-0-ethyl derivative (79) was of considerably lower activity when compared with the 7-0-methyl derivative (55), probably as a result of steric effects. Although 6-hydroxylation had a negative effect on activity (compare 54 with 57), it was found that 6-methoxylation markedly increased activity (compare 55 with 77). Based on the high activity of the 6,7-methylenedioxy-substituted flavone (6) and the 6,7-dimethoxy derivative (77), the presence of small alkoxy groups at C-6 and C-7 would seem to be effective in enhancing the zoospore attractant properties (Table 12) [83]. 

There were no difficulties when 3-methyl substituted 4-cyclohexene-1,2-di-carboxylic acid or its diglycidyl ester was epoxidized with PAA. The yield and properties of the synthesized triepoxides (XXXVII, Scheme 41) are given in Table 7 [25,26]. 

Stereochemical relationships play an especially important role in the properties of polymers. Consider the three polypropylene segments illustrated as Fischer projections in Figure 2.35. In the isotactic polymer, all of the methyl-substituted carbon atoms have the same configuration. In the syndiotactic polymer, the methyl-substituted carbon atoms have alternating configurations. In the atactic polymer there is a random pattern of configurations at the methyl-substituted carbon atoms. As with smaller molecules, the physical properties of diastereomeric polymers differ. Table 2.2 shows file relationship between tacticity and properties of polypropene. ... 

Since the cyanobiphenyl derivatives had proved to be excellent materials for electro-optic displays, equivalent homopolymer poly-siloxane liquid crystals, based on these low molar mass mesogens, were synthesized. Their properties are summarized in Table 1. Since the homopolymers only exhibited smectic phases, copolymers were prepared using destabilizing 2-methyl-substituted ester side-groups. As shown in Table 2, at sufficiently high ester-group concentrations, a... 

Thermodynamic contributions from the internal rotation of several symmetric tops may be readily calculated by appropriate summation of terms in Table 4. Few reliable calculations, however, have been reported. Thermodynamic properties of propane and several methyl-substituted benzenes have been reported, for example, but subsequent more accurate work has shown the necessity for considering that the internal rotation may be restricted. " Although the subsequent calculations for m-xylene and p-xylene used 6-fold internal rotation barriers of 2.1 to 3.1 kJ mol", more recent statistical calculations for toluene employing the presence of free rotation suggest that internal rotation in the two xylenes may be effectively unrestricted. 

From the kinetic properties of L-aminoamidase (Table 9) it can be concluded that an additional methylene group adjacent to the C atom in the a-methyl-substituted substrate results in an increased affinity of the enzyme for this substrate. On the other hand, much lower affinities are observed for substrates with a bulky group directly adjacent to the C atom. Finally, the purified enzyme displays L-selective amino acid amide hydrolase activity toward both a-H- and a-alkyl-substituted amino acid amides. The enzyme has the lowest enantioselectivity toward alanine amide E 25). 

Mechanical Properties Related to Polymer Structure. Methacrylates are harder polymers of higher tensile strength and lower elongation than thek acrylate counterparts because substitution of the methyl group for the a-hydrogen on the main chain restricts the freedom of rotation and motion of the polymer backbone. This is demonstrated in Table 3. 

Table 3.5-1 lists the E-r values for the allcylammonium thiocyanates and nitrates and the substituted imidazolium salts. It can be seen that the values are dominated by the nature of the cation. For instance, values for monoallcylammonium nitrates and thiocyanates are ca. 0.95-1.01, whereas the two tetraalkylammonium salts have values of ca. 0.42-0.46. The substituted imidazolium salts lie between these two extremes, with those with a proton at the 2-position of the ring having higher values than those with this position methylated. This is entirely consistent with the expected hydrogen bond donor properties of these cations. 

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