Cross polarization and magic angle sample spinning NMR spectra of model organic compounds. 3. Effect of the /sup 13/C-/sup 1/H dipolar interaction on cross polarization and carbon-proton dephasing. [4-ethoxyphenylacetic acid; bis(3,5 ditert-butyl-4-hydroxybenzyl) ether; 3,5-diisopropylphenol]

Journal Article · Wed Nov 02 00:00:00 EST 1983 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00360a025· OSTI ID:5237616

Alemany, L B; Grant, D M; Alger, T D; Pugmire, R J

Carbon-13 NMR studies involving conventional cross polarization and dipolar dephasing techniques at a variety of contact and delay times, respectively, provide valuable information on the magnitude of /sup 13/C-/sup 1/H dipole-dipole interactions. In solids whose spectra have overlapping resonances, such techniques discriminate between protonated and nonprotonated carbons. In dipolar dephased spectra, dipolar and rotational modulation of the resonances can occur for methine and methylene carbons, which are strongly coupled to the directly bonded protons. Methyl carbons exhibit a very wide range of effective dipolar couplings because of rapid methyl rotation that varies depending upon the structural environment. Dipolar modulation in methyl groups is not observed. Carbon atoms in tert-butyl methyl groups experience even weaker effective dipolar interactions than other methyl carbon atoms. These motionally decreased dipolar interactions are similar to those experienced by the quaternary aliphatic carbon atom. Steric crowding of a tert-butyl group on an aromatic ring causes (on the average) one of its methyl groups to differ in mobility from the other two. A biexponential decay not evident in any of the other functional groups studied results for both the quaternary and methyl carbons in the tert-butyl group. Nonprotonated sp/sup 2/-hybridized carbon atoms also exhibit weak dipolar couplings because of the remoteness of protons. The magnitude of the coupling varies substantially as a result of variations in motional freedom and structure. 8 figures, 2 tables.

• Research Organization: Univ. of Utah, Salt Lake City
• DOE Contract Number: AC02-78ER05006
• OSTI ID: 5237616
• Journal Information: J. Am. Chem. Soc.; (United States), Vol. 105:22
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ACETIC ACID ESTERS
NMR SPECTRA
ETHERS
PHENOLS
DATA ACQUISITION
EXPERIMENTAL DATA
PULSE TECHNIQUES
STRUCTURAL CHEMICAL ANALYSIS
TEMPERATURE DEPENDENCE
ULTRALOW TEMPERATURE
AROMATICS
CARBOXYLIC ACID ESTERS
DATA
ESTERS
HYDROXY COMPOUNDS
INFORMATION
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
SPECTRA
400301* - Organic Chemistry- Chemical & Physicochemical Properties- (-1987)