title: A study of conformational stability and vibrational assignments of 1-aminocyclopropanecarboxylic acid c-C3H4(NH2)-COOH.
abstract: The structural stability of 1-aminocyclopropanecarboxylic acid was investigated at DFT-BLYP, DFT-B3LYP and ab initio MP2 levels of theory with 6-311G(**) basis set. The molecule was predicted at the three levels of calculation to exist in cis-syn<-->trans-syn conformational equilibrium. The equilibrium constants for the conformational interconversion were calculated and found to correspond to an equilibrium mixture of about 35% cis-syn and 65% trans-syn conformations at 298.15 K. The cis-trans rotational barrier and the NH(2)syn-anti inversion barrier were estimated to be about 6 and 7 kcal/mol, respectively. The O-H rotational barrier was calculated to be of the order 12-14 kcal/mol. The vibrational frequencies of the two stable conformers of the acid were computed at the BLYP and the B3LYP levels of theory. Only vibrational assignments were provided for the low energy trans-syn conformer on the basis of normal coordinate analysis and experimental data. No clear evidence was found for the presence of the second high energy cis-syn structure in the spectra of the molecule.
authors.affiliation: Department of Chemistry, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia. hbadawi@kfupm.edu.sa
authors.forename: Hassan M
authors.initials: HM
authors.lastname: Badawi
mesh_terms: D000598:Amino Acids, Cyclic / Q000737:chemistry*; D003198:Computer Simulation; D007536:Isomerism; D008958:Models, Molecular; D008968:Molecular Conformation; D013055:Spectrophotometry, Infrared; D013059:Spectrum Analysis, Raman; D013816:Thermodynamics
chemical_list: D000598:Amino Acids, Cyclic; C023863:1-aminocyclopropane-1-carboxylic acid