By the methyl group

The water repeUency of sUicone finishes results from the low CST (ca 22 mN/m or dyne/cm) produced by the methyl groups in the sUicone that are oriented away from the fiber surface. The CST is lower than that produced by any class of compounds except for fluorochemicals. 

The classical theory of methylation with diazomethane was developed by Arndt from a different basis. It depends on the postulate (which can be traced back to von Pechmann " 0 of direct methylation mobile hydrogen in an acid compound is directly replaced by the methyl group, i.e., the methyl group appears in the place which the hydrogen previously occupied. For the reaction of tautomeric substances with diazomethane, the following equation is applicable ... 

Unlike unsubstituted and 3,4-disubstituted 1H-azepine-1 -carboxylates, which dimerize on heating, methyl 2-methyl-l//-azepine-l-carboxylate remains unchanged at 130 C, but on heating to 200°C ring contracts to Ar-(methoxycarbonyl)-2-methylaniline (64% mp 60°C).115 Similarly, the 4,5-dimethyl- and 3,6-dimethyl-l//-azepine-1-carboxylates, in which [6 + 4] dimerization is sterically retarded by the methyl groups, give only the A-arylurethanes. Methyl 2,7-dimethyl-1//-azepine-1-carboxylate is particularly stable and remains unchanged even after 24 hours at 200 C. 

The C2 symmetry of sulfide 13 means that a single diastereomer is formed upon alkylation (Scheme 1.10). Attack from the Si face of the ylide is preferred as the Re face is shielded by the methyl group cis to the benzylidene group (28). Metzner postulates that this methyl group also controls the conformation of the ylide, as a steric clash in 27b renders 27a more favorable [16]. However, computational studies by Goodman revealed that 27a was not particularly favored over 27b, but it was substantially more reactive, thus providing the high enantioselectivity observed... 

The relative graduation of ECT and x(HOMO) is not influenced during variation of X by introduction of a methyl group at a- and p-position. However, ECT as well as x(HOMO) are shifted in the direction of increased donor ability of the monomer by the methyl group. This shift is much more visible at the p-position than the a-position, for instance, the CT energy is decreased by an a-methyl group by 9 kJ mol-1 and by P-methyl group by about 24 kJ mol-1 (see Table 12). 

N-Benzoyl-Lalanine methyl ester is in turn about eight times more reactive than is its D enantiomer). The open-chain compounds may not bind to the enzyme in the same manner, however, as does the locked substrate. The conformation around the amido bond of the open-chain compounds, for example, can be transoid rather than cisoid (81). In addition, if equatorial 24 is considered to be the reactive conformer for both the Dand L enantiomers, and if the alanine methyl group is attracted to the hydrophobic aromatic binding subsite, then structures 34 and 38 would result. The L enantiomer of N-benzoyl-phenylalanine methyl ester 38 in this representation has approximately the same conformation as equatorial L-24. But attraction of the methyl of the D enantiomer to the location occupied by the methyl group of the L enantiomer causes the carbomethoxy group to move from the position it occupies in D-24. 

The 3-21+G reaction path to 13 is illustrated in Figure 7 and involves the intermediacy of the ion-dipole complex 12. As shown in Figure 5, the well-depth for 12 is reduced to 14.3 kcal/mol since the chloride ion is kept by the methyl group about 1.5 A farther from the carbonyl carbon than in 9. This interaction energy for Ci" CH3C0Ci compares favorably with the value of 11 kcal/mol estimated by Asubiojo and Brauman from their ICR experiments (4). 

The rearrangement ions [M —OH] , [M —H20] and [M — H2O- -OH] (equation 30) were not present if 63 had no ortho methyl substituent but they were present in all of 64. Accordingly, at least one of the eliminated hydrogens must be supplied by the methyl group and not by the aromatic rings. Some formation of [M — SO2] occurred also in both 63 and 64. 

A crystal structure is available for the SnCl4 complex of 2-benzyloxy-3-pentanone.89 The steric shielding by the methyl group with respect to the C=0 is evident in this structure (Figure 2.1). NMR studies indicate that the reaction involves... 

Synthetic Applications of the Diels-Alder Reaction. Diels-Alder reactions have long played an important role in synthetic organic chemistry.74 The reaction of a substituted benzoquinone and 1,3-butadiene, for example, was the first step in one of the early syntheses of steroids. The angular methyl group was introduced by the methyl group on the quinone and the other functional groups were used for further elaboration. 

The use of substitution at the 3-position to modify the steric environment about the metal center has been described in Section II,D,1. In a similar vein, substitution at the remote 5-position has been used with the specific goal of providing steric protection for the B-H moiety in attempts to inhibit ligand degradation. Indeed, as will be described, the steric protection that is provided by the methyl groups of the... 

Treatment of ZnMe2 with the thallium salt of a bis(pyrazolyl)hydroborate gave the methylzinc complex [BpZnMe] 104 in which zinc is three coordinate.162 This complex reacted with paraformaldehyde, Scheme 73, with the direct insertion of the CH20 moiety into the B-H bond to produce the methylzinc complex 105 (Figure 51), in which zinc is tetrahedrally surrounded by the methyl group and the newly formed N,N,O-ligand.163... 

After several years of effort it has been possible to reproduce Schmidbaur fs addition of methyliodide W The problem appears to be that the methyliodide product is extremely photosensitive in solution. It decomposes with the production of methyl radicals and the ultimate formation of a mixture of the Au(I), and Au(II) diiodide products. The X-ray crystal structure of the methyliodide product is presented in Figure 5. Two features are to be noted. Firstly, the metal-metal distance lengthens only a small amount, 0.04A, but the Au iodide distance lengthens by approximately 0.20. The structural trans effect caused by the methyl group is not attenuated by the Au-Au bond. 

Complex C (Scheme 21) seems to shows stable penta-coordination for apparently very different reasons. The compound is cationic, but the counterion is a non-coordinating tetraarylborate. Interestingly, neither the dichloromethane solvent nor the diethylether present in the reaction mixture seem to coordinate to the open site in solution. The compound was crystallized from a tetrahydrofuran/pentane mixture as the tetrahy-drofuran (THF) solvate, but in the crystal structure, the THF is remote from the open site at platinum. The open site is shielded somewhat by the methyl groups of the protonated TpMe2 ligand, but it does not appear completely inaccessible. A reasonable explanation for the... 

Compare with this the greater susceptibility to substitution caused by OH and NH2 and even by the methyl group in toluene. Trinitrotoluene is manufactured on a large scale as an explosive. 

The dipole moment of phosphabenzene is reinforced by the methyl group shown in (147) and increases it from 1.46 to 1.77 D thus it resembles pyridine, which has the heteroatom at the negative end of the dipole.181 The magnitudes and trends of the dipole moments of the methylphosphines have been investigated by MO studies and the dipoles partitioned into bond moments, bond polarization, and lone-pair moments.182 The reciprocal effects of the double bond and the phosphorus atom in... 

The chemical structure of PO differs from EO by the methyl group (-CH3), as shown in Figure 11-1. The difference is more than just a matter... 

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