Neopentyl group

Despite the anhydride stmcture, it is remarkably stable, surviving addition to the highly alkaline viscose, the acidic coagulating bath, and also resisting multiple laundering of the rayon fabric. The unusual stability may be attributed to the sulfur atoms, which enhance hydrophobicity, and to the stericaHy hindering neopentyl groups that retard hydrolysis. 

Neopentyl group, 89 S j2 reaction and, 366 Neoprene, synthesis and uses of,... 

A graphic demonstration of the importance of steric factors on kJkK is provided by the contrasting behavior of radicals 30 and 31. The sclf-rcaction of cumyl radicals (30) affords predominantly combination while the radical 31, in which an a-methyl is replaced by a neopentyl group, gives predominantly disproportionation. 65... 

The dynamic resolution of an aldehyde is shown in Figure 8.40. The racemization of starting aldehyde and enantioselective reduction of carbonyl group by baker s yeast resulted in the formation of chiral carbon centers. The enantiomeric excess value of the product was improved from 19 to 90% by changing the ester moiety from the isopropyl group to the neopentyl group [30a]. 

Reactions favoring [2 + 2] cycloaddition tended to be those that had strongly electronegative groups on the sp2-hybridized silicon but only H and the neopentyl group on the sp2-hybridized carbon atom. Butadiene and cyclohexadiene generally favored [2 + 2] cycloaddition with these silenes. The [2 + 2] adducts with cyclohexadiene appear to be kinetic products, since they cleanly isomerized to the Diels-Alder adducts over time.182... 

The common name neopentyl group is approved by the IUPAC. 

Entries 10 and 11 were obtained by the reaction of the bridged tetrachlorides Cl2RSn(CH2)4SnRCl2 with the polymeric bridged oxides [R1(0)Sn(CH2)4Sn(0)R1]B. In the crystal, the neopentyl groups occupy the outer four corners of the tetrameric block in solution, the tetramers are in equilibrium with their corresponding mixed dimers. 

It may be concluded from the different examples shown here that the enantioselective copper-catalyzed allylic substitution reaction needs further improvement. High enantioselectivities can be obtained if chirality is present in the leaving group of the substrate, but with external chiral ligands, enantioselectivities in excess of 90% ee have only been obtained in one system, limited to the introduction of the sterically hindered neopentyl group. 

C-13 nmr spectra were taken of all the alkali metal compounds of I and II from Li to Cs. As expected, changing the counter-ion had very little effect on the chemical shifts of the carbons in the neopentyl group in either I or II, or on the extra methyl group in II, compared with the parent hydrocarbon ( 3). 

Formation of XXVII by loss of a proton from the tertiary carbon atom in the neopentyl group of XXVI rather than from the tertiary carbon atom in the secondary isopentyl group is, however, hardly to be expected. Furthermore, the addition of a tertiary olefin to a secondary carbonium ion is also unexpected (compare the results on the copolymerization of n-butylene with isobutylene, page 46). A somewhat more likely combination consists of the addition of the tertiary carbonium ion. XXVIII to fert-butylethylene (XXIX) followed by a 1,3-shift of a... 

The fact that about five times as much of 2,3,4,4-tetramethyl-l-pentene (XXXVIII) was obtained as its 2-isomer (XXXIX) indicates that the loss of a proton from either of the two methyl groups takes place about five times as easily as do the loss of the proton on the tertiary carbon atom that is part of the neopentyl system. Similarly, the relative amounts of 3,5,5-trimethyl-2-hexene and its 3-isomer (XL and XLI) indicates that the loss of a proton from the ethyl group occurs about five times as readily as from the neopentyl group no loss of a proton from the methyl group appears to have occurred. By analogy with the formation of the two isomeric diisobutylenes from the ear-bonium ion VI it would be expected that the carbonium ion XLII which leads to the formation of 2,4,4-trimethyl-2-hexene (XLIII) would yield the 1-isomer in about four to five times the amount of the 2-isomer. The failure to find any of the 1-isomer was little less than startling (Whitmore and Mixon, 47). 

The structure of cyclopentadienyl(neopentyl)magnesium (65) in the gas phase has been determined by gas-phase electron diffraction . The Mg—C bond distances of the rf-bonded cyclopentadienyl group are 2.328(7) A while the Mg—C bond distance of the neopentyl group was found to be 2.12(2) A. 

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