6533b7cffe1ef96bd1258dd6
RESEARCH PRODUCT
Why betaine crystallizes in high local C s symmetry. An ab initio MO and DFT study of anhydrous betaine and betaine monohydrate
Ilkka PitknenTommi H. NyrnenReijo Suontamosubject
Crystallographychemistry.chemical_compoundBetaineStereochemistryChemistryHydrogen bondIntramolecular forceAnhydrousAb initioMoleculeTrimethylglycinePhysical and Theoretical ChemistryBasis setdescription
A theoretical study of the structure, charge distribution, rotational barrier and fundamental vibrations of anhydrous betaine (CH3)3NCH2COO (trimethylglycine) was carried out and compared with available experimental data. Calculations were carried out at HF, MP2 and B3LYP levels using a 6-31+G(d,p) basis set. The calculated rotational barrier of the betaine carboxylic group is 40.5 kJ/mol at the MP4(SDQ)/6-311G(d,p)//HF/6-31+G(d,p) level of theory. The rotation of the carboxylic group changes the molecule from a highly symmetric (C s ) conformation into a twisted conformation resulting in shortening of the molecule by about 50 pm. Natural population analysis (NPA) indicates intramolecular interaction between the carboxylic oxygen and the nearest methyl hydrogens resulting in internal hydrogen bonding. MP4(SDQ)/6-311G(d,p) single-point NPA calculations on a betaine monohydrate model taken from the X-ray geometry show an expected weakening in the internal hydrogen bond. Calculations explain why betaine preferentially crystallizes in high local C s symmetry.
| year | journal | country | edition | language |
|---|---|---|---|---|
| 1999-02-15 | Theoretical Chemistry Accounts: Theory, Computation, and Modeling (Theoretica Chimica Acta) |