Configurational methyl

Influence of the Configuration, Methylation, and the Counterions on Transfection Efficiency... 

Bonner et al. found that the hydrogenolysis of optically active methyl or ethyl atrolac-tates (48, X = OH) in refluxing ethanol with large amounts of Raney Ni proceeded largely with retention of configuration methyl D-(+)-2-phenyl-2-methoxypropionate... 

The cobalt(I) cobalamin catalyzed reduction of a-methyl-a,P-unsaturated carbonyl compounds produces the corresponding saturated derivatives having an (5)-configuration at the a-carbon (Scheme 81) 424 highest enantiomeric excess (33%) is exhibited by the (Z)-configurated methyl ketone. The... 

Baker s yeast reduction of methyl 2-(l,3-dithian-2-yl)-3-oxobutanoate gives the syn-configurated methyl (2R,3S)-2-(l,3-dithian-2-yl)-3-hydroxybutanoate in 42% yield and high diastereo- and enantioselectivity (92% de, >99% ee)225. Reduction of the ethyl ester shows a similar selectivity with a chemical yield of 62%. 

Another study confirms the spacing criticality and shows different negative contributions of R- and S-configured methyl groups in the 4-position (30). Different negative effects for 2- and 3-OH... 

The observed rotational transitions are split due to the internal rotation of the methyl group. Structural data See [OOCam] (Planar configuration, methyl group anti to the phenyl ring). 

Fig. 2. Atrolactic acid method for the correlation of configuration, methyl group is added from the least hindered side of carbonyl.

The FAB-m.s. and tandem m.s. anal is of nearly thirty chemicalfy modified cyclodextrins has been reported. Tandem FAB-m.s. studies on a series of isomeric methyl glycopyranosides have demonstrated that the intensities of the [M + K] ions relative to those of the [DEA +K] ions (where DEA = diethanolamine) produced by CAD (as alternative firagments of the selected [M + K -t- DEA]" " precursor cluster ions) are sensitive to sugar configuration. Methyl o-D-talopyranoside yielded the most intense [M + K] ion because it complexes the potassium ion strongest. ... 

Hase W L 1972 Theoretical critical configuration for ethane decomposition and methyl radical recombination J. Chem. Rhys. 57 730-3... 

Pig. 2. By replacing the methyl group in p-methlyphenol with a series of softcore iiitcTaction sites it is possible to spread the range of configurations sampled to include configurations with and without a cavity in the para position. 

Epoxides and aziridines are also capable of electrophilic subsitution of indoles. Indolylmagncsium bromide and cyclohexene oxide react to give 3-(lrans-2-hydroxycyclohexyl)indole[14]. Reaction of indoles with epoxides also occurs in the presence of Lewis acids. For example, indole reacts with methyl 2S,3R-epoxybutanoate at C3 with inversion of configuration[15]. 

The pair of isomers designated as and trans 2 butene have the same constitution both have an unbranched carbon chain with a double bond connecting C 2 and C 3 They differ from each other however m that the cis isomer has both of its methyl groups on the same side of the double bond but the methyl groups m the trans isomer are on oppo site sides of the double bond Recall from Section 3 11 that isomers that have the same constitution but differ m the arrangement of their atoms m space are classified as stereoisomers as 2 Butene and trans 2 butene are stereoisomers and the terms as and trans specify the configuration of the double bond... 

This compound therefore has the R configuration It is (/ ) (+) 2 methyl 1 butanol... 

Compounds in which a chirality center is part of a ring are handled in an analo gous fashion To determine for example whether the configuration of (+) 4 methyl cyclohexene is R or S treat the right and left hand paths around the nng as if they were independent substituents... 

Representation of the polymer chain in an extended zigzag conformation as shown m Figure 7 16 reveals several distinct structural possibilities differing with respect to the relative configurations of the carbons that bear the methyl groups... 

Which product compound A B or C would you expect to be formed when 1 methyl 1 2 epoxycyclopentane of the absolute configuration shown IS allowed to stand in methanol containing a few drops of sulfuric acid Compare your answer with that given for Problem 16 13... 

Gutta percha is a natural polymer of isoprene (3-methyl-l,3-butadiene) in which the configuration around each double bond is trans. It is hard and horny and has the following formula ... 

The features that occur near 5 = 1.0 ppm are associated with the protons of the a-methyl group. The location of this peak depends on the configurations of the nearest neighbors. 

Optically active 2-arylalkanoic acid esters have been prepared by the Friedel-Crafts alkylation of arenes with optically active a-sulfonyloxy esters (40). Friedel-Crafts alkylation of ben2ene with (5)-methyl 2-(chlorosulfonyloxy)- or 2-(mesyloxy)propionate proceeded with predorninant inversion of configuration (<97%) to give (5)-methyl 2-phenylpropionate. 

DUactide (5) exists as three stereoisomers, depending on the configurations of the lactic acid monomer used. The enantiomeric forms whereia the methyl groups are cis are formed from two identical lactic acid molecules, D- or L-, whereas the dilactide formed from a racemic mixture of lactic acid is the opticaUy iaactive meso form, with methyl groups trans. The physical properties of the enantiomeric dilactide differ from those of the meso form (6), as do the properties of the polymers and copolymers produced from the respective dilactide (23,24). 

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