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Effect of chain length on the glyme-separated ion-pair formation in bolaform salts of α,ω-(9-fluorenyl)polymethylenes (1978)

Collins, George L. ; Hogen Esch, Thieo E. ; Smid, Johannes

Springer

Journal of solution chemistry 7 (1978), S. 9-18

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ISSN: 1572-8927

Keywords: Optical spectroscopy ; bolaform electrolytes ; ion pairs ; ion-pair aggregation ; glyme-separated ion pairs ; α,ω-(9-fluorenylsodium)-polymethylenes ; fluorenylsodium ; tetraglyme ; tetrahydrofuran ; tetrahydropyran

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Abstract Formation constants of tetraglyme (glyme 5) separated ion pairs of bolaform electrolytes of the type Na+,−Fl(CH2) n Fl−, Na+ (Fl− denoting a fluorenyl carbanion) were measured spectrophotometrically in tetrahydrofuran (THF) and tetrahydropyran (THP) at 25°C as a function of the chain lengthn, withn=2, 3, 4, or 6. The ratiosK 1/K 2 of the first and second glyme ion-pair separation steps were found to be equal to the statistical factor 4 in all cases except in THP for the compoundn=2, where the ratio is 15. Values ofK 1 as well as K 2 increase considerably with chain length, the former by a factor 19 asn increases from 2 to 6. The ion-pair separation with glyme 5 is easier in THP than in THF. The results are discussed in terms of differences in external cation solvation and the possible involvement of cyclized structures or curled conformations as a result of interactions between the terminal ion pairs.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00654214

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Stereochemical control in anionic polymerization of 2-vinylpyridine and related vinyl monomers (1995)

Hogen-Esch, Thieo E. ; Jin, Qiao ; Dimov, Dimo

Chichester : Wiley-Blackwell

Journal of Physical Organic Chemistry 8 (1995), S. 222-230

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ISSN: 0894-3230

Keywords: Organic Chemistry ; Physical Chemistry

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Physics

Notes: The alkylation, silylation and other electrophilic reactions of 1-lithio-1,3-bis(2-pyridyl)butane (2a) in THF at -78°C leads to meso-like products that may be accounted for by intramolecular coordination of Li ion with the penultimate 2-pyridyl group. This is also demonstrated by proton-transfer equilibria between 1-lithio-2-ethylpyridine and 2a, allowing the determination of the ΔH and ΔS of intramolecular chelation in 2a. The ΔS of chelation is nearly zero, probably as a result of chelation-induced desolvation of Li ion. Surprisingly, however, the corresponding addition of 2-vinylpyridine to 2a and higher P2VPLi homologs in THF is not stereoselective. In toluene at -78°C the t-BuLi-initiated polymerization of 2-VP is actually somewhat syndiotactic (rr = 0·44). The presence in this polymerization of at least one equivalent of t-BuOLi or other tertiary ROLi surprisingly leads to isotactic P2VP. SEC viscometric and other studies indicate that both the P2VPLi- and P2VPLi-ROLi complexes are monomeric in toluene. The stereochemistry is apparently due to a 1 : 1 P2VPLi-ROLi complex that discriminates between the two pro-chiral faces of the anion by preferntial coordination of the (ROLi2) moiety to the meso-prochiral face. Isotactic-like addition now occurs by electrophilic attack of 2-VP that is syn with respect to the (ROLi2) ‘counter ion.’

Additional Material: 2 Ill.