Medium-Dependent Crossover from the Red to Blue Shift of the Donor’s Stretching Fundamental in the Binary Hydrogen-Bonded Complexes of CDCl₃ with Ethers and Ketones

Abstract

Mid-infrared spectra for C–D···O hydrogen (H)-bonded binary complexes of CDCl3 with acetone (AC), cyclohexanone (CHN), diethyl ether (DEE), and tetrahydrofuran (THF) have been measured in the vapor phase at room temperature and in an argon matrix at 8 K. Remarkable matrix effect has been observed in each case with respect to the spectral shift of the donor group’s stretching fundamental (ΔνC–D). In the case of complexes with AC and CHN, the sign of ΔνC–D changes from a few wavenumbers positive (blue shift) in the vapor phase to a few tens of wavenumbers negative (red shift) in the argon matrix. For the two ether complexes, although no apparent reversal in the sign of ΔνC–D occurs, but the magnitudes of the red shifts in the matrix are manifold larger, and the bands appear with large enhancement in transition intensity. The medium effect has been explained consistently in terms of the local hyperconjugative charge transfer interaction at the H-bonding sites of the complexes and its interplay with the H-bond distance that varies with the physical conditions of the medium. Under the matrix isolation condition, νC–D bands of CHN and THF complexes depict a large number of substructures, which has been interpreted in terms of matrix site effect as well as Fermi resonance enhancement of the fingerprint combination tones and trapping of more than one isomer of the complexes in the matrix sites.

Factors contributing to halogen bond strength and stretch or contraction of internal covalent bond

“…One of the more intriguing developments in the H-bond field was the recent discovery that a number of HBs ignore this rule, and shift their AH stretching frequency to the blue. [21][22][23][24][25][26][27][28][29][30][31] In these cases, the bond length also changes in the opposite direction, contracting instead of elongating. After some initial thought that perhaps this contrary behavior disqualified these interactions as true H-bonds, it was soon agreed that they are indeed H-bonds in all respects, despite their unexpected spectral behavior.…”

Role of O–H⋯O/S conventional hydrogen bonds in considerable Csp2–H blue-shift in the binary systems of acetaldehyde and thioacetaldehyde with substituted carboxylic and thiocarboxylic acids

“…36 A slight C sp 3-H stretching frequency blue-shi of 8.7 cm −1 in C sp 3-H/N nonconventional hydrogen bond was recently observed in the complex between chloroform with acetonitrile in the gas phase using Fourier transform IR (FTIR) spectroscopy by Behera et al 27 Remarkably, a similar change of the C sp 3 -H stretching frequency from blue shi in the gas phase to red shi in the argon matrix was also observed in complexes of deuterated chloroform with acetone and cyclohexanone. 37 Recently, the blue shi of the stretching frequency was found in the C sp 2 -H bond and the extent of stretching frequency was even much higher than that of the C sp 3 -H bond as a proton donor, in spite of the larger polarity of the former with respect to the latter one. Indeed, a C sp 2 -H signicant blue shi by 81 O 96 cm −1 in the C sp 2 -H/O hydrogen bond formed in the complexes of formic acid with formaldehyde and thioformaldehyde has been recently discovered.…”

“… 36 A slight C sp 3 –H stretching frequency blue-shift of 8.7 cm −1 in C sp 3 –H⋯N nonconventional hydrogen bond was recently observed in the complex between chloroform with acetonitrile in the gas phase using Fourier transform IR (FTIR) spectroscopy by Behera et al 27 Remarkably, a similar change of the C sp 3 –H stretching frequency from blue shift in the gas phase to red shift in the argon matrix was also observed in complexes of deuterated chloroform with acetone and cyclohexanone. 37 …”

Confinement effects on C–H and C–F stretching vibrational frequencies of difluoromethane in cold inert gas matrixes: a combined infrared spectroscopy and electronic structure theory study

“…The other interesting examples are the hindrance of the proton tunnelling in the double-well potential of malonaldehyde [5], and disappearance of the signatures of rotational motion of water, compared to that in the vapour phase [6]. Very recently, Bhattacharya et al [7] have demonstrated that the spectral shifts for the C-D stretching vibration of CDCl 3 in the binary C-D• • • O hydrogen bonded complexes between CDCl 3 and various ethers and ketones are significantly altered, both in terms of sign and magnitude, when confined in an argon matrix compared to the shifts observed in the gas phase. Similar changes in spectral shifts of the C-H stretching fundamental of chloroform of the hydrogen bonded binary CHCl 3 -NH 3 complex were also reported.…”