Influence of Substitution, Hybridization, and Solvent on the Properties of C−HO Single-Electron Hydrogen Bond in CH3−H2O Complex

Evidence For a Water-Stabilised Ion Radical Complex: Photoelectron Spectroscopy and Ab Initio Calculations

A photoelectron spectrum corresponding to an unknown 174m/z anion complex has been recorded. Initially believed to be I−…CH3CH2OH (173m/z), the spectrum has been assigned as belonging to that of an I−…H2O…CH3CH2 radical anion complex. The major peaks in the photoelectron spectrum occur at 3.54eV and 4.48eV as the 2P3/2 and 2P1/2 spin-orbit states of iodine respectively. Ab initio calculations were performed in order to rationalise the existence of the complex, with all structures converging to a ‘ring-like’ geometry, with the iodide anion bound to both the water molecule as well as a hydrogen of the ethyl radical, with the other hydrogen of water bound to the unpaired electron site of the ethyl. Simulated vertical detachment energies of 3.59eV and 4.53eV were found to be in agreement with the experimental results.

Triel bonds in RZH2···NH3: hybridization, solvation, and substitution

The influence of hybridization, substitution, and solvation on the triel bond has been investigated in the complexes of RZH₂···NH₃ (Z = B and Al). The magnitude of the π-hole on the triel atom is related to the nature of the Z atom and the hybridization of R. CH₃BH₂ has the largest π-hole among RBH₂, while for RAlH₂ the largest π-hole is found in CH≡CAlH₂. The interaction energy is partly inconsistent with the magnitude of the π-hole on the triel atom and the orbital interaction from the N lone pair of NH₃ into the empty p orbital of the triel atom. The strongest B···N triel bond is found in CH≡CBH₂···NH₃, while the weakest Al···N triel bond is in CH₃AlH₂···NH₃. The strength of the triel bond is increased in solvents, and its enhancement is prominent with the increase of solvent polarity. Solvents also change the nature of the Al···N triel bond from an electrostatic interaction to a partially covalent one. The F substituent in the triel donor strengthens the triel bond, depending on the substitution position and number. Graphical Abstract The π-hole triel bonded complexes between RZH2 (Z =B and Al) and NH3 have been investigated. We focused on the effects of hybridization, solvent, and substitution on the strength and nature of π-hole triel bond.

Dual role for alkali metal cations in enhancing the low-temperature radical polymerization of N,N-dimethylacrylamide

Alkali metal cations, including the Li⁺ cation, have been proposed to play a dual role in radical polymerization of N,N-dimethylacrylamide.

A σ-hole interaction with radical species as electron donors: does single-electron tetrel bonding exist?

A single-electron tetrel bond was predicted and characterized in FXH₃⋯CH₃ (X = C, Si, Ge, and Sn) complexes.

Triplex blue-shifting hydrogen bonds of ClO4(-)···H-C in the nanointerlayer of montmorillonite complexed with cetyltrimethylammonium cation from hydrophilic to hydrophobic properties

In this study, molecular interactions of perchlorate (ClO4(-)), an emerging pollutant, with cetyltrimethylammonium(CTMA(+)) complexed in the nanointerlayer of negatively charged montmorillonite were characterized using the zeta potentials, FTIR, Raman, and XRD spectroscopy and quantified using quantum mechanical calculations and sorption experiments. We found that blue-shifting hydrogen bonds assisted in the uptake of ClO4(-) from water into the nanointerlayer spacing of CTMA(+)-montmorillonite and were tunable according to CTMA(+) loading. FTIR spectra presented an obvious 47 cm(-1) blue shift in the C-H vibration coming from the N-terminal methyl group of CTMA(+) when ClO4(-) was absorbed. Quantum mechanical calculations based on density functional theory demonstrated that triplex blue-shifting hydrogen bonds of C-H···O were formed between the three terminal methyl groups of CTMA(+) and three oxygen atoms of ClO4(-). The contribution of blue-shifting hydrogen bonds to perchlorate uptake switched from a ClO4(-)/CTMA(+) ratio of 0.0453 at low CTMA(+) loadings to a ClO4(-)/CTMA(+) ratio of 0.2563 (5.6-fold) at high CTMA(+) loadings, which can be ascribed to the evolution of the nanointerlayer microenvironments from hydrophilic properties to hydrophobic properties. The blue-shifting hydrogen bond of C-H···O that is tunable with the hydrophobic nature of the organic phase should be recognized to elucidate the biochemical behavior of perchlorate in organisms.

Effect of the resonance of the C-H and O-H bond stretching vibrations on the IR spectra of the hydrogen bond in formic and acetic acid

It is shown that the resonance of the O-H and C-H bond stretching vibrations is responsible for a noticeable intensity redistribution effect in the IR spectra of associated formic acid molecules in the gaseous phase. This effect is manifested by a considerably high growth in intensity of the νC-H band, which overlaps the νO-H band contour in the spectra. A vibronic coupling of the Herzberg-Teller-type expressed by the second order term in the perturbation theory is the most probable source of these spectral effects. The presented mechanism explains the variation of the effect magnitude accompanying the phase transitions. The proposed model also facilitates the understanding of the H/D isotopic effects in the spectra as well as the essential difference in the corresponding spectral properties between the formic and the acetic acid.

Weak H-bonds. Comparisons of CH···O to NH···O in proteins and PH···N to direct P···N interactions

Whereas CH···O H-bonds are usually weaker than interpeptide NH···O H-bonds, this is not necessarily the case within proteins. The nominally weaker CH···O are surprisingly strong, comparable to, and in some cases stronger than, the NH···O H-bonds in the context of the forces that hold together the adjacent strands in protein β-sheets. The peptide NH is greatly weakened as proton donor in certain conformations of the protein backbone, particularly extended structures, and forms correspondingly weaker H-bonds. The PH group is a weak proton donor, but will form PH···N H-bonds. However, there is a stronger interaction in which P can engage, in which the P atom, not the H, directly approaches the N electron donor to establish a direct P···N interaction. This approach is stabilized by the same sort of electron transfer from the N lone pair to the P-H σ* antibond that characterizes the PH···N H-bond.

Ab initio study of lithium-bonded complexes with carbene as an electron donor

The complexes H(2)C-LiX (X = H, OH, F, Cl, Br, CN, NC, CH(3), C(2)H(3), C(2)H, NH(2)) have been studied with quantum chemical calculations at the MP2/6-311++G(d,p) level. A new type of lithium bond was proposed, in which the carbene acts as the electron donor. This new type of lithium bond was characterized in view of the geometrical, spectral and energetic parameters. The Li-X bond elongates in all lithium bonded complexes. The Li-X stretch vibration has a red shift in the complexes H(2)C-LiX (X = H, OH, F); however, it exhibits a blue shift in the complexes H(2)C-LiX (X = Cl, Br, CN, NC, CH(3), C(2)H(3), C(2)H, NH(2)). The binding energies are in a range of 16.88-21.13 kcal/mol, indicating that the carbene is a good electron donor in the interaction. The energy decomposition analyses show that the electrostatic contribution is largest, polarization counterpart is followed, and charge transfer is smallest. The effect of substitution and hybridization on this type of lithium bond has also been investigated.