Conformational equilibrium of formanilide: detection of the pure rotational spectrum of the tunnellingcisconformer

Abstract

2005)Conformational equilibrium of formanilide: detection of the pure rotational spectrum of the tunnelling cis conformer, Formanilide has been investigated by molecular beam Fourier transform microwave spectroscopy. The rotational spectra of two conformers, with the formyl hydrogen cis or trans with respect to the phenyl group have been measured. Their relative energy has been estimated to be 350 AE 150 cm À1 , the trans form being more stable. In the cis species the plane of the pseudo-peptidic group forms an angle of AE34.7(5) (equilibrium value) with the ring. The two equivalent configurations, corresponding to the þ or -sign, are tunnelling through a barrier to planarity of 152(2) cm À1 .

Stepwise Microhydration of Aromatic Amide Cations: Formation of Water Solvation Network Revealed by Infrared Spectra of Formanilide+–(H2O)n Clusters (n ≤ 5)

“…This result is consistent with previous molecular beam experiments 55,60,61 but is quite different from observations in microwave and solution experiments reporting a roughly equal population of both rotamers at room temperature. 54,56,67 Interestingly, the calculations suggest that the planarity of the amide group and its coplanarity with the phenyl ring are not much affected by the microhydration of the amide group in FA + −(H 2 O) n , in line with the high torsional barriers for both internal rotations.…”

“…61 These values are in accordance with the theoretical predictions. 54,56,61,62,68 Isomer-selective IR spectra of t-/c-FA recorded in the hydride stretch (amide A, ν NH , ν CH ) and fingerprint (amide I−II) ranges demonstrate the large structural differences of the amide groups in the two isomers. 59,60 Interestingly, clusters of FA with polar (L = H 2 O) and nonpolar ligands (L = Ar) have so far only been observed for the more stable t-FA rotamer.…”

The complete conformational panorama of formanilide–water complexes: the role of water as a conformational switch

“…The angle between the amide and the phenyl ring in the cis configuration defined as the dihedral angle C 1 -N-C 2 -C 3 was found experimentally to be 34.7. 22 The trans configuration is planar.…”

“…17,18 Formanilide (N-phenylformamide, C 7 H 7 NO, see Scheme 1) is a formamide derivative which presents a cis-trans conformational equilibrium. [20][21][22] In fact, a MB-FTMW study has shown that both forms of formanilide are present in the supersonic expansion being the trans conformer most stable by ca. 350 cm 1 .…”

“…350 cm 1 . 22 In this context, the observation of the microsolvated clusters of cis-and trans-formanilide would allow exploring the diverse interaction sites between Scheme 1. Formanilide in the cis (left) and trans (right) configurations.…”