Cryospectroscopic and ab initio studies of haloform–trimethylamine H-bonded complexes

Isotope Effects on the Vaporization of Organic Compounds from an Aqueous Solution-Insight from Experiment and Computations

An isotope fractionation analysis of organic groundwater pollutants can assess the remediation at contaminated sites yet needs to consider physical processes as potentially confounding factors. This study explores the predictability of water–air partitioning isotope effects from experiments and computational predictions for benzene and trimethylamine (both H-bond acceptors) as well as chloroform (H-bond donor). A small, but significant, isotope fractionation of different direction and magnitude was measured with ε = −0.12‰ ± 0.07‰ (benzene), ε_C = 0.49‰ ± 0.23‰ (triethylamine), and ε_H = 1.79‰ ± 0.54‰ (chloroform) demonstrating that effects do not correlate with expected hydrogen-bond functionalities. Computations revealed that the overall isotope effect arises from contributions of different nature and extent: a weakening of intramolecular vibrations in the condensed phase plus additional vibrational modes from a complexation with surrounding water molecules. Subtle changes in benzene contrast with a stronger coupling between intra- and intermolecular modes in the chloroform–water system and a very local vibrational response with few atoms involved in a specific mode of triethylamine. An energy decomposition analysis revealed that each system was affected differently by electrostatics and dispersion, where dispersion was dominant for benzene and electrostatics dominated for chloroform and triethylamine. Interestingly, overall stabilization patterns in all studied systems originated from contributions of dispersion rather than other energy terms.

The infrared study of fluoroform + methyl fluoride mixtures in argon and nitrogen matrices. Evidence of nonlinear blue-shifting complex formation

The FTIR spectra of fluoroform + methyl fluoride mixtures trapped in argon and nitrogen matrices are studied at T~10-30 K. Spectroscopic changes observed in the region of the CH stretching mode of fluoroform are typical for weak blue shifting H - bonds of CH⋯F type. The degeneracy lifting effect found on E - type bands of fluoroform interacted with methyl fluoride suggests the complex formation of a nonlinear form. The experimental results are confirmed by ab initio calculations of fluoroform + methyl fluoride based on the second order Møller-Plesset theory of perturbations utilizing advanced basis set. Nonlinear complexes are stabilized by the basic CH⋯F interaction and additionally by van der Waals-type CD⋯FC contacts between deuterated methyl fluoride and fluoroform.

Infrared photodissociation spectroscopy of cold cationic trimethylamine complexes

Infrared spectroscopic studies reveal the general trends in the stepwise growth motif of trimethylamine (TMA)_n⁺ complexes.

Identification and H(D)-bond energies of C-H(D)Cl interactions in chloride-haloalkane clusters: a combined X-ray crystallographic, spectroscopic, and theoretical study

The cationic (1,3,5-triazapentadiene)Pt(II) complex [Pt{NH[double bond, length as m-dash]C(N(CH2)5)N(Ph)C(NH2)[double bond, length as m-dash]NPh}2]Cl2 ([]Cl2) was crystallized from four haloalkane solvents giving [][Cl2(CDCl3)4], [][Cl2(CHBr3)4], [][Cl2(CH2Cl2)2], and [][Cl2(C2H4Cl2)2] solvates that were studied by X-ray diffraction. In the crystal structures of [][Cl2(CDCl3)4] and [][Cl2(CHBr3)4], the Cl(-) ion interacts with two haloform molecules via C-DCl(-) and C-HCl(-) contacts, thus forming the negatively charged isostructural clusters [Cl(CDCl3)2](-) and [Cl(CHBr3)2](-). In the structures of [][Cl2(CH2Cl2)2] and [][Cl2(C2H4Cl2)2], cations [](2+) are linked to a 3D-network by a system of H-bondings including one formed by each Cl(-) ion with CH2Cl2 or C2H4Cl2 molecules. The lengths and energies of these H-bonds in the chloride-haloalkane clusters were analyzed by DFT calculations (M06 functional) including AIM analysis. The crystal packing noticeably affected the geometry of the clusters, and energy of C-HCl(-) hydrogen bonds ranged from 1 to 6 kcal mol(-1). An exponential correlation (R(2) > 0.98) between the calculated Cl(-)H distances and the energies of the corresponding contacts was found and used to calculate hydrogen bond energies from the experimental Cl(-)H distances. Predicted energy values (3.3-3.9 kcal mol(-1) for the [Cl(CHCl3)2](-) cluster) are in a reasonable agreement with the energy of the Cl3C-HCl(-) bond estimated using ATRFTIR spectroscopy (2.7 kcal mol(-1)).

Complexes of carbon dioxide with dihalogenated ethylenes: structure, stability and interaction

Interactions of ethylene and its 1,2-dihalogenated derivatives with CO₂ induce twenty four molecular complexes with stabilization energies in the range of 1.1 to 7.5 kJ mol⁻¹ as computed at the CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVDZ level of theory.

Infrared spectroscopy and ab initio study of hydrogen bonded Cl3CD·N(CH3)3 complex in the gas phase

FTIR spectra of the gas phase Cl3CD+TMA mixture have been studied at room temperature in ∼800-4000 cm(-1) frequency domain. The formation of the H-bonded Cl3CD…TMA complex has been detected. Spectroscopic parameters of the band ascribed to the complex were evaluated. MP2 frozen core ab initio calculations have been carried out with the Pople-type 6-311++G(d,p) basis set. The equilibrium geometries and harmonic vibrational frequencies of the complex were obtained using CP-corrected gradient techniques. The ''freq=anharm'' option has been tested for Cl3CD monomer and Cl3CD…TMA complex to examine possible anharmonic effects on the vibrations localized on the proton donor. The effects of Darling-Dennison and Fermi resonances on the frequency of the stretching vibration of the CH proton donor were analyzed.

Remarkable effects of substitution on stability of complexes and origin of the C–H⋯O(N) hydrogen bonds formed between acetone's derivative and CO2, XCN (X = F, Cl, Br)

What are the important factors affecting C–H bond length changes in C–H⋯O and C–H⋯N hydrogen bonds?

A theoretical investigation on the conformation and the interaction of CHF₂OCF₂CHF₂ (desflurane II) with one water molecule

The conformation and the interaction of CHF₂OCF₂CHF₂ (desflurane II) with one water molecule is investigated theoretically using the ab initio MP2/aug-cc-pvdz and DFT-based M062X/6-311++G(d,p) methods. The calculations include the optimized geometries, the harmonic frequencies of relevant vibrational modes along with a natural bond orbital (NBO) analysis including the NBO charges, the hybridization of the C atom and the intra- and intermolecular hyperconjugation energies. In the two most stable conformers, the CH bond of the F2HCO- group occupies the gauche position. The hyperconjugation energies are about the same for both conformers and the conformational preference depends on the interaction between the non-bonded F and H atoms. The deprotonation enthalpies of the CH bonds are about the same for both conformers, the proton affinity of the less stable conformer being 3 kcal mol−1 higher. Both conformers of desflurane II interact with water forming cyclic complexes characterized by CH…O and OH…F hydrogen bonds. The binding energies are moderate, ranging from −2.4 to −3.2 kcal mol−1 at the MP2 level. The origin of the blue shifts of the ν(CH) vibrations is analyzed. In three of the complexes, the water molecule acts as an electron donor. Interestingly, in these cases a charge transfer is also directed to the non bonded OH group of the water molecule. This effect seems to be a property of polyfluorinated ethers.

Strong hyperconjugative interactions in isolated and water complexes of desflurane: a theoretical investigation

Ab initio MP2/aug-cc-pvDZ and density functional B3LYP calculations with the 6-311++G(d,p) basis set are performed to investigate the conformation of desflurane (CHF2OCHFCF3), its acidity/basicity and its interaction with one water molecule. The calculations include the optimized geometries, the harmonic frequencies of relevant vibrational modes, the binding energies with water, and a detailed natural bond orbital (NBO) analysis Iincluding the NBO charges, the hybridization of the C atoms and the intra- and intermolecular hyperconjugations. The relative energies of the two most stable conformers are discussed as a function of the total hyperconjugative energies resulting from the interaction of lone pairs of the O and F atoms to the different antibonding orbitals of desflurane. The proton affinity is the same for both conformers but the acidity of the CH bond is larger for the less stable conformer. The binding energies of the complexes of two desflurane conformers with one water molecule range from -2.75 to -3.23 kcal mol(-1). Depending on the structure of the complexes, the CH bonds involved in the interaction are contracted or elongated. The σ*(CH) occupation predominates over the hybridization effect in determining the CH bond length. There is an unexpected charge transfer to the external OH bond of the water molecule. This effect is in good agreement with theoretical data on the complexes between fluorinated dimethyl ethers and water and seems to depend on the number of F atoms implanted on the ether molecule.