How water links to cis and trans peptidic groups: the rotational spectrum of N-methylformamide\u2013water

We investigated the Fourier transform microwave spectra of the hydrated forms of the N-methylformamide (NMF) in a supersonic expansion and assigned the rotational spectra of two mono-hydrated species. The conformation of each molecular complex was reliably determined on the basis of the values of the rotational constants, of the relative intensities of a- and b-type transitions, and of the features of the 14N quadrupole hyperfine structure of the rotational transitions. In both complexes water acts as a proton donor and NMF has a trans configuration of the peptidic group. In the most stable of these conformers, water is also weakly bound to the methyl group

The two conformers of acetanilide unraveled using LA-MB-FTMW spectroscopy

Acetanilide has been investigated by laser ablation molecular beam Fourier transform microwave LA-MB-FTMW spectroscopy. The rotational spectrum of both trans and cis conformers have been analyzed to determine the rotational and 14N quadrupole coupling the constants. The spectrum of the less abundant cis conformer has been assigned for the first time. The doublets observed for this conformer have been interpreted in terms of the tunneling motion between two equivalent non-planar conformations through a small barrier in which the acetamide group and phenyl ring plane are perpendicular. The results are compared with those of the related formanilide

Tautomerism and Microsolvation in 2-Hydroxypyridine/2-Pyridone

The Fourier transform microwave spectra of the hydrated forms of the tautomeric pair 2-pyridinone/2-hydroxypyridine (2PO/2HP) has been investigated in a supersonic expansion. Three hydrated species, 2PO-H2O, 2HP-H2O, and 2PO-(H2O)2, have been observed in the rotational spectrum. Each molecular complex was confidently identified by the features of the 14N quadrupole hyperfine structure of the rotational transitions. The presence of water affects the tautomeric equilibrium \u2013N=C(OH)\u2013  \u2013NH\u2013C(=O)\u2013, which is shifted to the enol form for the bare molecules 2PO/2HP but to the keto tautomer for the hydrated forms

Nuclear quadrupole coupling interactions in the rotational spectrum of tryptamine

Four conformers of tryptamine have been detected in a supersonic expansion and characterized by laser ablation molecular beam Fourier transform microwave spectroscopy LA-MB-FTMW in the 5\u201310 GHz frequency range. The quadrupole hyperfine structure originated by two 14N nuclei has been completely resolved for all conformers and used for their unambiguous identification. Nuclear quadrupole coupling constants of the nitrogen atom of the side chain have been used to determine the orientation of the amino group involved in N\u2013H p interactions: to the p electronic system of the pyrrole unit in the Gauche-Pyrrole conformers (GPy) or to the phenyl unit in the Gauche-Phenyl ones

Protic Group Tunnelling in the 1:1 Complexes of Dimethylether with HF, HCl and H2O

The rotational spectra of the molecular adducts concerning dimethylether (DME) show interesting features such as: (i) three weak C-H 7 7 7O improper H-bonds in the DME-DME dimer [1] and, (ii) the tunnelling splittings of Ar and Ne in the 1:1 complexes with DME [2,3]. Here we report the results of the studies on the interactions of DME with strong proton donors such as H2O, HF and HCl. All of them tunnel between the two lone pairs of the O atom of DME, generating huge inversion splittings in the rotational spectra. From them it has been possible to determine the rates and pathways of the inversion processes. . Millimeter wave absorption free jet and molecular beam Fourier transform microwave spectroscopy techniques have been used for the experiments.DME 7 7 7HCl is shown on the figure to the right. HCl is tunnelling from above to below the COC plane with a frequency of 8215.7 MHz. [1] \u2013 Y. Tatamitani, B. Liu, J. Shimada, T. Ogata, P. Ottaviani, A. Maris, W. Caminati and J. L. Alonso, J. Am. Chem. Soc., 124 (2002) 2739. [2] \u2013 P. Ottaviani, A. Maris, W. Caminati, Y. Tatamitani, Y. Suzuki, T. Ogata and J. L. Alonso, Chem. Phys. Letters, 361 (2002) 341. [3] \u2013 A. Maris and W. Caminati, J. Chem. Phys., 118 (2003) 1649