Conformational studies by dynamic NMR. 33. Possible applications of the magic angle spinning technique for identifying meso and racemic conformers in the solid state

Journal Article · Fri Jan 08 04:00:00 EST 1988 · J. Org. Chem.; (United States)

DOI:https://doi.org/10.1021/jo00236a035· OSTI ID:6333917

Casarini, D; Lunazzi, L; Macciantelli, D

The /sup 13/C magic angle spinning NMR spectrum of a meso compound in the solid often displays a different number of lines with respect to its racemic isomer. Usually the meso isomers that have a symmetric conformation in the crystal are expected to yield the same spectral multiplicity as in solution (e.g., meso-2,3-dimethylsuccinic acid). Exceptions might in principle occur in the few cases when the center of molecular symmetry is not coincident with a center of crystallographic symmetry: examples of this type, however, were not encountered in the present work. On the other hand the isomeric racemic derivatives are normally expected to have solid-state spectra with a larger number of lines than in solution (e.g., d,l-2,3-dimethylsuccinic acid). In a very limited number of cases solid-state spectra with unsplit lines can be encountered: an example (trans-1,2-cyclohexanedicarboxylic acid) is reported here and discussed. In the case of N,N'-diisopropyl-N,N'-dimethyl-1,5-naphthyldiamine (1) the /sup 13/C solution spectrum at -90/degrees/C does show the existence of two conformers with unequal proportions: one of them being meso, the other racemic. The solid-state spectrum of 1 shows that some of the lines of the major conformer are split into two with respect to the solution spectrum whereas those of the minor conformer are unsplit, as in solution. On this basis the racemic structure has been tentatively assigned to the major conformer and the meso structure to the minor conformer. In favorable circumstances, as those here reported, these features might possibly be helpful in discriminating meso from racemic conformers when they cannot be physically separated nor investigated by X-ray diffraction.

• Research Organization: Universita, Bologna (Italy)
• OSTI ID: 6333917
• Journal Information: J. Org. Chem.; (United States), Journal Name: J. Org. Chem.; (United States) Vol. 53:1; ISSN JOCEA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
400202 -- Isotope Effects
Isotope Exchange
& Isotope Separation
ALKANES
AMINES
AROMATICS
CARBON 13
CARBON ISOTOPES
CARBOXYLIC ACIDS
CONDENSED AROMATICS
CYCLOALKANES
CYCLOHEXANE
DATA
DICARBOXYLIC ACIDS
EVEN-ODD NUCLEI
EXPERIMENTAL DATA
HYDROCARBONS
INFORMATION
ISOMERS
ISOTOPES
LIGHT NUCLEI
MOLECULAR STRUCTURE
NAPHTHALENE
NMR SPECTRA
NUCLEI
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
SPECTRA
STABLE ISOTOPES
SUCCINIC ACID