1495-14-3Relevant academic research and scientific papers
Complete 13C NMR Spectra of the Axial Forms of Methyl- Ethyl- and Isopropylcyclohexane
Squillacote, Michael E.,Neth, Joann M.
, p. 53 - 56 (1987)
Low temperature 13C NMR spectral data have been obtained for equatorial and axial methyl- ethyl- and isopropylcyclohexane using a high-temperature cryogenic trapping technique. 13C chemical shift differences between major and minor conformations of each compound are discussed in terms of chemical shift theories.A convenient synthesys of deuteriated dichlorofluoro- and difluorochloromethane, which are excellent low-temperature NMR solvent, is also presented. - KEY WORDS Low temperature 13C NMR; methylcyclohexane; ethylcyclohexane; isopropylcyclohexane; axial and equatorial conformers.
Symmetrization of cationic hydrogen bridges of protonated sponges induced by solvent and counteranion interactions as revealed by NMR spectroscopy
Pietrzak, Mariusz,Wehling, Jens P.,Kong, Shushu,Tolstoy, Peter M.,Shenderovich, Ilya G.,Lopez, Concepcion,Claramunt, Rosa Maria,Elguero, Jose,Denisov, Gleb S.,Limbach, Hans-Heinrich
experimental part, p. 1679 - 1690 (2010/06/17)
The properties of the intramolecular hydrogen bonds of doubly 15N-labeled protonated sponges of the 1,8-bis(dimethylamino)naphthalene (DMANH+) type have been studied as a function of the solvent, counteranion, and temperature using low-temperature NMR spectroscopy. Information about the hydrogen-bond symmetries was obtained by the analysis of the chemical shifts δH and δN and the scalar coupling constants J(N,N), J(N,H), J(H,N) of the 15NH15N hydrogen bonds. Whereas the individual couplings J(N,H) and J(H,N) were averaged by a fast intramolecular proton tautomerism between two forms, it is shown that the sum | J(N,H)+J(H,N)| generally represents a measure of the hydrogen-bond strength in a similar way to δH and J(N,N). The NMR spectroscopic parameters of DMANH+ and of 4-nitro-DMANH+ are independent of the anion in the case of CD3CN, which indicates ion-pair dissociation in this solvent. By contrast, studies using CD2Cl2, [D8]toluene as well as the freon mixture CDF3/ CDF2Cl, which is liquid down to 100 K, revealed an influence of temperature and of the counteranions. Whereas a small counteranion such as trifluoroa-cetate perturbed the hydrogen bond, the large noncoordinating anion tetrakis[3,5-bis(trifluoromethyl)phenyl]borate B[{C6H3(CF3)2}4] - (BARF-), which exhibits a delocalized charge, made the hydrogen bond more symmetric. Lowering the temperature led to a similar symmetrization, an effect that is discussed in terms of solvent ordering at low temperature and differential solvent order/disorder at high temperatures. By contrast, toluene molecules that are ordered around the cation led to typical high-field shifts of the hydrogen-bonded proton as well as of those bound to carbon, an effect that is absent in the case of neutral NHN chelates.
