NH Stretching Vibrations of Jet-Cooled Aniline and Its Derivatives in the Neutral and Cationic Ground States

Abstract

NH stretching vibrations of jet-cooled aniline and its various derivatives were observed in the neutral and cationic ground states. Infrared-ultraviolet double-resonance spectroscopy was utilized for the observation in the neutral ground state, and autoionization-detected infrared spectroscopy was used in the measurement of the cationic ground state. Low-frequency shifts of the NH frequencies were seen upon ionization, though the magnitude of the shifts was much smaller than those of the OH stretching vibrations observed for phenol derivatives. NH vibrational frequencies of meta and para isomers of aniline derivatives showed a positive correlation with the Hammett σ parameters of the substituents in the neutral ground state, while a negative correlation was found for the cationic ground state. Intramolecular hydrogen bond formation was found for o-cyanoaniline in both the neutral and cationic ground states based on the infrared spectra of deuterated isotopomers as well as theoretical calculations, showing that the hydrogen bond strength is remarkably enhanced upon ionization.

Microsolvation of the 4‐Aminobenzonitrile Cation (ABN+) in a Nonpolar Solvent: IR Spectra of ABN+Ln (L=Ar and N2, n≤4)

“…The NÀH stretching fundamentals of neutral AN were measured in S 0 to be n a/s = 3508/3421 cm À1 ; [68] [68] are slightly larger than those in ABN + by Dn a/s = + 4/ + 3 cm À1 , [19] again in line with the predicted shifts ofDn a/s = + 6/ + 5 cm…”

“…As a consequence of the slightly weaker and longer NÀH bonds, the NH 2 group in ABN + is more acidic, and thus, a better proton donor than that in AN + , leading to stronger hydrogen bonds and larger accompanying Dn a/s shifts upon hydrogen bonding ( Figure S2 + relative to AN + has previously been rationalized by the presence of the electron-withdrawing CN group, which in turn increases conjugation of the lone pair of the planar NH 2 group with the aromatic p electrons, and thus, electron transfer from the NÀH bonding orbitals to the positively charged aromatic ring. [68] This view is supported by the NBO analysis of ABN + and AN + and is described in Figure S3 in the Supporting Information. H!CN substitution increases the positive partial charge on the NH 2 group by 0.01 e and that on the C 6 H 4 ring skeleton by 0.16 e. Thus, the hydrogen and p bonds become stronger upon substitution of the CN group (Table 1).…”

The World of Non-Covalent Interactions: 2006

“…an infrared absorption is characterized by an ion dip. This type experiment has been very successful, and with the advent of new optical parametric IR laser sources the OH and NH 31 vibration region of various species has been extensively probed.…”

Resonance-enhanced multiphoton ionization (REMPI) spectroscopy of the 35Cl and 37Cl isotopomers of p-chloroanisole

“…Due to the natural abundance of chlorine isotopes, the 35 Cl and 37 Cl isotopomers of p-chloroanisole were detected by high-resolution time-of-flight (TOF) mass spectrometry, and thus, the resonance-enhanced two-photon ionization (R2PI) spectra [12,13] of the two isotopomers were measured. Because the R2PI process occurs when the laser wavelength is tuned to an intermediate state of the molecule, the R2PI spectrum of pchloroanisole not only provides useful information about the molecular properties, but also presents a promising method for the determination of p-chloroanisole [14,15].…”