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Titolo:
AN EVALUATION OF THE OVERALL ROTATIONAL CORRELATION TIMES OF TETRAALKYLAMMONIUM IONS IN SOLUTION - C-13 NMR RELAXATION STUDY
Autore:
MASUDA Y; TOBITA J; MURAMOTO A;
Indirizzi:
OCHANOMIZU UNIV,FAC SCI,DEPT CHEM,BUNKYO KU TOKYO 112 JAPAN
Titolo Testata:
Bulletin of the Chemical Society of Japan
fascicolo: 7, volume: 71, anno: 1998,
pagine: 1555 - 1563
SICI:
0009-2673(1998)71:7<1555:AEOTOR>2.0.ZU;2-E
Fonte:
ISI
Lingua:
ENG
Soggetto:
NUCLEAR MAGNETIC-RESONANCE; AQUEOUS-SOLUTIONS; CONCENTRATION-DEPENDENCE; DIELECTRIC FRICTION; LIQUIDS; MOTION; RAMAN; SPECTROSCOPY; MODEL; FLUID;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
52
Recensione:
Indirizzi per estratti:
Citazione:
Y. Masuda et al., "AN EVALUATION OF THE OVERALL ROTATIONAL CORRELATION TIMES OF TETRAALKYLAMMONIUM IONS IN SOLUTION - C-13 NMR RELAXATION STUDY", Bulletin of the Chemical Society of Japan, 71(7), 1998, pp. 1555-1563

Abstract

The C-13 NMR spin-lattice and spin-spin relaxation times (T-1 and T-2), and the nuclear Overhauser effect (NOE) were measured for tetraalkylammonium ions (R4N+, R= C2H5 (EI), n-C3H7 (n-Pr), n-C4H9 (n-Bu), and n-C5H11 (n-Pen)) in the concentrated aqueous solutions of their bromides or chlorides. A minimum was observed in the temperature dependence of T-1 for the alpha-carbon in each solution. The value was 1.2-1.4 times higher than that predicted assuming only the isotropic overall rotation of the R4N+ ion. This increase in the T-1 minimum values was ascribed to the rotations around the N-alpha-C bonds with an restriction in the azimuthal angle for each bond. The ranges where the N-alpha-C bonds could rotate with the time scales much less than those for the overall rotations were determined by the values of the T-1 minima for the corresponding R4N+ ions as +/-20 degrees, +/-17 degrees, +/-20 degrees, and 1200 centering the gauche conformations, respectively, for Et4N+, n-Pr4N+, n-Bu4N+, and n-Pen(4)N(+). These values well reproduced the T-2 and NOE values observed at various temperatures in the concentrated aqueous solutions of the R4N+ halides. By using the thus obtainedranges of the azimuthal angles, the overall rotational correlation times in the dilute aqueous solutions (0.01 mol kg(-1)) were also determined. The obtained rotational correlation times were compared with those calculated using the Stokes-Einstein-Debye equation and the effect of the hydrophobic hydration was discussed.

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Documento generato il 11/07/20 alle ore 16:55:10