Lateral methyl substituent

Large lateral groups e.g., alkyl ehains) have been included in mesogenic materials (e.g., 102a) for purely academic purposes. A lateral methyl substituent (102b) causes a significant depression in T j despite the position of substitution being relatively... 

Broer, D. J., Boven, J., Mol, G. N., and Challa, G., In situ photopolymerization of oriented liquid-crystalline acrylates 4. Influence of a lateral methyl substituent on monomer and oriented polymer network properties of a mesogenic diacrylate, Makromol. Chertt, 190, 2255, 1989. 

The effect of lateral methyl groups in the spacer on the phase behavior has been studied in several polybibenzoates [18,19] derived from poly(tetramethy]ene p,p bibenzoate), P4MB. The branched polymers display transition temperatures significantly lower than P4MB. Moreover, the substituents have a clear effect on the kind of mesophase formed. Thus, P4MB displays a smectic A mesophase, while the lateral methyl groups... 

These two studies highlight the high reactivity of C-H bonds close to Ru. Consequently, Gmbbs later reported a catalyst in which rotation of the phenyl group is restricted by methyl substituents at the 4-position of the NHC, thus preventing decomposition by C-H activation [50],... 

Many other structural variants were pursued, the most beneficial being the introduction of fluorine or methyl at the 6a position and, later, methyl at the 16a or 16(3 position. Considerable improvements in biological activity were also created by esterification of hydroxyl substituents at C-17 and C-21. Some aspects of the synthesis of the 16-methyl glucococorticoids are detailed later in a summary of some of the work undertaken by my colleagues in Schering. 

Table 9.7. When the aromatic reactant carries an EWG, the selectivity increases, since the TS occurs later. For example, while toluene is about 20 times more reactive than benzene, /j-nitrotoluene is about 200 times more reactive than nitrobenzene. The effect of the methyl substituent is magnified as a result of the later TS. 

Highly substituted cyclohexanes and cyclopentanes have been prepared by means of a cascade process involving the use of a nitroalkene as Michael acceptor and an a-substituted p-ketoester incorporating a lateral p-substituent with a terminal methyl ketone moiety at the convenient position, ready to... 

In 2000, MacMillan and his co-workers presented the first enantioselective organocatalytic 1,3-dipolar cycloaddition of nitrones 187 and a,p-unsaturated aldehydes 28 (dipolarphiles) to afford the e do-(45)-isoxazolidine adducts 188, Scheme 3.59 [75]. With the LUMO-lowering activation of a,p-unsaturated aldehydes 28 and enforced formation of (fi)-iminium isomer, the HClO -salt of catalyst 30 effectively promote cycloaddition of the dipolarphile. In addition, e do-cycloaddition effectively alleviated nonbonding interaction between the nitrone phenyl group and the neopentyl methyl substituent on the catalyst framework. Later, in 2002, Karlsson and Hbgberg reported the organocatalytic enantioselective 1,3-dipolar cycloaddition of... 

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