A convenient method for obtaining free energies of activation by the coalescence temperature of an unequal doublet

Shanan-Atidi, H.; Bar‐Eli, K.

doi:10.1021/j100699a054

Cited by 351 publications

(160 citation statements)

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“…An analytical method, however, has been developed for estimating the activation free energies for a 2:1 site exchange. 46 This method is outlined in the Experimental Section, and the values obtained for the activation energies given in Table 7 are reasonable as they are similar to those in Table 6. c As T c and ∆ν are determined by an extrapolation of the temperature dependence of the CMe 3 protons in C 7 D 8 as described in the Experimental Section.…”

Section: (D) Quantitative Evaluation Of the N-cme 3 Rotation Barriersupporting

confidence: 54%

Coordination of 1,4-Diazabutadiene Ligands to Decamethylytterbocene: Additional Examples of Spin Coupling in Ytterbocene Complexes

2007

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The paramagnetic 1:1 coordination complexes of (C 5 Me 5 ) 2 Yb with a series of diazabutadiene ligands, RN=C(R')C(R')=NR, where R= CMe 3 , CHMe 2 , adamantyl, p-tolyl, p-anisyl, and mesityl when R'=H, and R= p-anisyl when R'= Me, have been prepared. The complexes are paramagnetic, but their magnetic moments are less than expected for the two uncoupled spin carriers, (C 5 Me 5 ) 2 Yb(III, 4f 13 ) and the diazabutadiene radical anions (S= ½), which implies exchange coupling between the spins. The variable temperature 1 H NMR spectra show that rotation about the R-N bond is hindered and these barriers are estimated. The barriers are largely determined by steric effects but electronic effects are not unimportant.2

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Section: (D) Quantitative Evaluation Of the N-cme 3 Rotation Barriersupporting

confidence: 54%

Coordination of 1,4-Diazabutadiene Ligands to Decamethylytterbocene: Additional Examples of Spin Coupling in Ytterbocene Complexes

2007

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“…8 Application of this equation to the two proton doublets at 7.85 and 7.63 ppm, which are assumed to coalesce at 323 K (Fig. 2), yields a free energy of activation of 67 kJ mol À1 .…”

Section: Resultsmentioning

confidence: 99%

NMR and semi-empirical study of the tautomerism of�2,2?-bisbenzimidazolyl

Zucco

Dall’Oglio

Salmoria

et al. 1998

J. Phys. Org. Chem.

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A dynamic NMR study of the tautomerism of 2,2'-bisbenzimidazolyl in DMSO-d 6 and a mechanistic interpretation of the process, based on a stepwise, single-proton transfer and formation of a zwitterionic intermediate, are presented. This interpretation is substantiated by semi-empirical calculations of the postulated intermediate and transition state, that yield results which are compared with previous studies on related aliphatic systems.

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“…The coalescence temperatures for the signals at 36.7 pprn and 66.5 pprn at -50 f 5°C and -57 * 5°C and chemical shift differences of 56.1 and 126.9 Hz, respectively, were used to calculate rate constants at coalescence of 191.1 and 84.5 s-I, respectively, by means of the method of ShananAtidi and Bar-Eli for unequally populated sites (25). Fractional populations for the two sites of 0.67 and 0.33 were used.…”

Section: Solution Nuclear Magnetic Resonance Spectral Resultsmentioning

confidence: 99%

The structure of 2,2-dibutyl-1,3,2-dioxastannane in the solid state and in solution

Grindley¹,

Thangarasa²,

Bakshi³

et al. 1992

Can. J. Chem.

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Can. J. Chem. 70, 197 ( 1 992).Crystals of 2,2-dibutylil,3,2-dioxastannane (I) are orthorhombic, of space group Pnma, with a = 7.663(3), b = 18.437(2), c = 9.277(4) A, Z = 4, R = 0.0568 (R,,. = 0.0551) for 1183 independent reflections with I > 3u(I). Compound 1 is a polymer in which each monomer unit i : joined to the next by a four-membered (SnOI? ring. The Sn-0 bond lengths inside the monomer units average 2.04 A while those between monomers average 2.57 A. The mirror plane of the crystal contains the atoms in the four-membered rings and the other oxygen atoms. Two of the three remaining carbon atoms in the six-membered rings of the monomer units are close to the mirror plane. The other carbon atom is disordered above and below the plane. It was shown by "'Sn NMR spectroscopy that solutions of 1 contain mixtures of oligomers that consist mainly of dimers, trimers, and tetramers in chloroform-d. AGO values for dimer-trimer equilibria and dimer-tetramer equilibria of -2.5 and -1.5 kcal mol-' were obtained from integration of low temperature " 9~n NMR spectra. These values favour the higher oligomers slightly less than those for 2,2-dibutyl-1,3,2-dioxastannolane.Key words: 1,3,2-dioxastannanes, stannylene acetals, X-ray crystallography, 'I9sn NMR spectroscopy. Le compose 1 est un polymkre dans lequel chaque unit6 de monomere est like a la suivante par un cycle aoquatre chainons (SnO),. La longueur moyenne des liaisons Sn-0 a l'intkrieur des unites de monomkre est tgale a 2,04 A alors que celle observke entre les monomkres est de 2,57 A. Le plan miroir du cristal contient les atomes des cycles a quatre chainons ainsi que les autres atomes d'oxygtne. Deux des trois autres atomes de carbone des cycles a six chainons des unites de monom6re se trouvent pres du plan miroir. L'autre atome de carbone est dCsordonnC au-dessus et au-dessous du plan.

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A convenient method for obtaining free energies of activation by the coalescence temperature of an unequal doublet

Cited by 351 publications

References 1 publication

Coordination of 1,4-Diazabutadiene Ligands to Decamethylytterbocene: Additional Examples of Spin Coupling in Ytterbocene Complexes

Coordination of 1,4-Diazabutadiene Ligands to Decamethylytterbocene: Additional Examples of Spin Coupling in Ytterbocene Complexes

NMR and semi-empirical study of the tautomerism of�2,2?-bisbenzimidazolyl

The structure of 2,2-dibutyl-1,3,2-dioxastannane in the solid state and in solution

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