Brightening and locking a weak and floppy N-H chromophore: the case of pyrrolidine.
The N-H stretching signature of the puckering equilibrium between equatorial and axial pyrrolidine is analyzed via FTIR and Raman spectroscopy in supersonic jets as a function of aggregation. Vibrational temperatures along the expansion axis can be extracted from the Raman spectra and allow for a localization of the compression shock waves. While the equatorial conformation is more stable in the ground state monomer, this preference is probably switched in the excited state with one N-H stretching quantum. Furthermore, the dominant dimer involves an axial donor and the trimer and tetramer structures seem to prefer uniform axial conformations. The IR intensity is boosted by up to 3 orders of magnitude upon aggregation, whereas the Raman scattering intensity shows only moderate hydrogen bond effects. B3LYP and MP2 calculations provide a reasonable description of the N-H vibrational dynamics under the influence of self-aggregation. In mixed dimers with pyrrole, pyrrolidine assumes the role of a hydrogen bond acceptor.
Hesse
Susanne
S
Institut für Physikalische Chemie, Universität Göttingen, Tammannstrasse 6, 37077 Göttingen, Germany.
Wassermann
Tobias N
TN
Suhm
Martin A
MA
D056004:Molecular Dynamics Simulation; D011759:Pyrrolidines / Q000737:chemistry*; D011789:Quantum Theory; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman; D013696:Temperature
D011759:Pyrrolidines; C032519:pyrrolidine