| Autor: |
Carol Sutcliffe, James M Hewitt, Allen D Godwin, George C. Levy |
| Rok vydání: |
1978 |
| Předmět: |
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| Zdroj: |
Journal of Magnetic Resonance (1969). 29:553-562 |
| ISSN: |
0022-2364 |
| DOI: |
10.1016/0022-2364(78)90013-6 |
| Popis: |
Combined use of carbon-13 and nitrogen-15 NMR spectral data can give unique insight into the molecular dynamics of nitrogen-containing organic compounds and ions. 13 C and 15 N spin-lattice relaxation data and chemical shifts are reported for aniline and also for o -, m -, and p -aminobenzoic acids in solution as the cations, anions, and neutral compounds. 15 N and 13 C dipolar T 1 values obtained as a function of temperature for aniline and anilinium ion allowed estimation of the activation energy for overall molecular reorientation ( 13 C T 1 's) and for the composite internal-overall motion of the amine functions ( 15 IN T 1 's). The calculated values using both nuclei were the same: 3 kcal mole −1 for aniline and 4.8 kcal mole −1 for anilinium ion. '3C spin-lattice relaxation times T 1 's for the neutral and ionized aminobenzoic acids probe inter- and intra molecular association through hydrogen bonding and ion pairing. 13 C and 15 N relaxation and shielding data give evidence for possible intramolecular association between the amine and carboxyl functions in ortho -aminobenzoic acid and its mono-ions. 15 N T 1 and nuclear Overhauser enhancement (NOE) data indicate that aniline or substituted aniline NH 2 or NH 3 + groups undergo rapid but not free internal rotation (and/or inversion in the case of NH 2 groups), at rates at least comparable with the rate of overall reorientation for these systems ( τ c ≈ 10 −10 sec). o- and m-Aminobenzoic acids are effectively diprotonated in CF 3 SO 3 H solution. 15 N T 1 's) and NOE's for these two species indicate that the NH 3 + groups spin essentially freely in this highly acidic, nonnucleophilic medium. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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