Carbon-13 spin-lattice relaxation in condensed aromatic compounds

Journal Article · Thu Mar 20 04:00:00 EST 1980 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100443a013· OSTI ID:5269896

Alger, T D ^[1]; Hamill, Jr, W D; Pugmire, R J; Grant, D M; Silcox, G D; Solum, M

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1. Utah State Univ., Logan

Several aromatic compounds (naphthalene, phenanthrene, pyrene, acenaphthene, and xanthone) have been studied at 25.1 and 75.3 MHz and 33/sup 0/C. The /sup 13/C spin-lattice relaxation measurements, T/sub 1/, are measured at the two frequencies along with determinations of the nuclear Overhauser enhancement (NOE). Independent estimations of the relaxation contributions are made for the dipolar and chemical shift anisotropy mechanisms. For the carbon-13 nuclei with attached protons, the NOE measurements range from a low of 2.7 to a maximum value of 3.0 (dominated by dipolar relaxation), and the values of T/sub 1/ are in the range of 3 to 11 s. Since dipolar mechanisms dominate, these values are relatively unaffected by field variations. In contrast, the values of the NOE parameter for nonprotonated carbons vary from 1.1 to 2.5. The average value of NOE in such cases is about 2.1 at 25.1 MHz and 1.5 at 75.3 MHz. For these nonprotonated carbons, the relative contributions of T/sub 1//sup D/ and T/sub 1//sup CSA/ at 25.1 MHz are approximately equal and relatively large (greater than 100 s and as large as 300 to 1000 s). In contrast, at 75.3 MHz the l/T/sub 1//sup CSA/ contribution dominates these nonprotonated carbons. The chemical shift anisotropic relaxation time T/sub 1//sup CSA/ is in the range of 30 to 90 s at this higher field strength. Chemical shift anisotropies similar to those measured in simple aromatic compounds (200 to 250 ppM) are adequate to account for the observed values of T/sub 1//sup CSA/.

• OSTI ID: 5269896
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 84:6; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ACENAPHTHENE
AROMATICS
CARBON 13
CARBON ISOTOPES
CONDENSED AROMATICS
DATA
DATA FORMS
EVEN-ODD NUCLEI
EXPERIMENTAL DATA
HETEROCYCLIC COMPOUNDS
HYDROCARBONS
INFORMATION
ISOLATED VALUES
ISOTOPES
LIGHT NUCLEI
NAPHTHALENE
NUCLEI
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
PHENANTHRENE
PURINES
PYRENE
RELAXATION
SPIN-LATTICE RELAXATION
STABLE ISOTOPES
XANTHINES