| Abstract
| - This work reports the first experimental study of the cyanoacetic acid (CAA) monomer. Samples of CAAwere isolated in low-temperature argon, krypton, and xenon matrixes and characterized using FTIRspectroscopy. Annealing experiments revealed the presence of different conformers in the matrixes. The directinterconversion of the gauche−cis (gc) into the cis−cis (cc) conformer was observed upon annealing ofmatrixes before formation of aggregates. The use of different matrix host gases enabled separation of theobserved conformational effects from the site-splitting of IR absorptions. The assignment of the experimentalspectra was based on both the annealing results and the comparison of the experimental data with results oftheoretical calculations performed at the B3LYP/aug-cc-pVTZ level of theory. The relative energies of theobserved conformers, as well as the transition states separating these forms, were calculated at the MP2,MP4, QCISD, and CCSD levels of theory with the aug-cc-pVxZ (x = D, T, and Q) basis sets. The planar ccconformer was found to be the lowest energy form of CAA. The second conformer, with a nonplanar backbone,gc, is doubly degenerated by symmetry and was predicted to be 1.3 kJ mol-1 (ZPVE corrected CCSD/aug-cc-VTZ energies) less stable than the cc form. In matrixes a fraction of the gc conformer undergoes geometricaldistortion toward the planar trans−cis (tc) structure, which in the gaseous phase corresponds to the saddlepoint between the two mirror gc forms.
|
