ChemInform Abstract: The Structure of Gaseous Cyclopropanecarboxylic Acid as Studied by Microwave Spectroscopy, Electron Diffraction and ab initio Calculations.

Abstract

structure structure (organic substances) K 9000 -060The Structure of Gaseous Cyclopropanecarboxylic Acid as Studied by Microwave Spectroscopy, Electron Diffraction and ab initio Calculations.-The syn-syn conformer is found to be the most stable one (Cs symmetry). - (MARSTOKK, K.-M.; MOELLENDAL, H.; SAMDAL, S.; Acta Chem. Scand. 45 (1991) 1, 37-45; Dep. Chem., Univ. Oslo, N-0315 Oslo, Norway; EN)

Microwave Spectrum for a Second Higher Energy Conformer of Cyclopropanecarboxylic Acid and Determination of the Gas Phase Structure of the Ground State

“…The bond angles in the ring remained fairly constant, with the angles changing by only 1°. The bond lengths within the cyclopropane ring also agree fairly well with previous structural work . Differences between these structures most likely arise from the combination of the microwave data with electron diffraction work since the diffraction structure will represent an average over vibrational and rotational states.…”

“…The fits for the rotational constants of the 13 C isotopologues of the low-energy CPCA conformer were performed using Pickett’s SPFIT program, and these results are shown in Table under the “experimental” column. During the fits of the 13 C transitions from the low-energy conformer, the centrifugal distortion constants were held fixed to the values obtained by Marstokk et al, due to these constants being measured for high J and K transitions and so likely to be more accurately determined. Also in Table are the rotational constants from the best-fit structure (under the “calculated” column) and the deviation of these constants for the best-fit structure from the experimentally determined values (m–c).…”

“…They are important throughout biology and can be synthesized and utilized for many important reactions. , Structural information on these types of molecules is important to obtain to understand the chemistry and reactivity behind these enzymatic processes in biology or reactions performed in the lab. Infrared, Raman, microwave, and X-ray crystal structure studies have been reported previously for cyclopropanecarboxylic acid (CPCA). − To obtain a more accurate gas-phase structure, transitions from 13 C singly substituted isotopologues were needed to continue from the previous work. This work extends the microwave spectroscopic work to include these 13 C measurements and allows us to obtain a best-fit gas-phase structure of CPCA.…”

“…From these ab initio calculations, it is reasonable that rotational transitions from this high-energy conformer should be observed but significantly weaker than the previously measured low-energy conformer. In the work by Marstokk et al, this higher-energy conformer was searched for in the 26.5–38.0 GHz range but was not observed, most likely due to the low abundance and low populations for the high- J transitions. In the present work, we report the microwave measurements and fits to determine rotational and centrifugal distortion constants of this higher-energy conformer of CPCA.…”