Evidence of the weakness of the OH⋯F hydrogen bond from a conformational study of 3-fluoro-1-propanol by microwave spectroscopy

The rotational spectra of the OH and OD isotopic species have been observed for three rotamers of 3-fluoro-1-propanol. One of them (HBC form) displays an internal hydrogen bond with a distorted chair conformation of the six-membered ring. The other two rotamers have the oxygen atom gauche with respect to the C₂C₃ bond, the hydroxyl hydrogen trans with respect to the C₁C₂ bond and the fluorine atom gauche (GGT form) and trans (TGT form), respectively, with respect to the C₂C₁ bond. The energies of the vibrational ground states of the HBC and TGT forms are ～0.4 and 1.0 kcal/mole higher than that of the GGT form, respectively (from relative intensity measurements). The hydrogen bond is therefore rather weak in this compound. With compounds capable of forming OH?O or OH?N bonds, the conformation appropriate for hydrogen bonding is normally the most stable form. Several excited states have been analyzed for the TGT and GGT rotamers in order to have additional data with respect to the potential function for the internal rotation about the C₃C₂ bond.     

The a-Type K = 0 Microwave Spectrum of the Methanol Dimer

The rotational spectrum of (CH₃OH)₂ has been observed in the region 4-22 GHz with pulsed-beam Fabry-Perot cavity Fourier-transform microwave spectrometers at NIST and at the University of Kiel. Each a-type R(J), K_a = 0 transition is split into 15 states by tunneling motions for (CH₃OH)₂, (¹³CH₃OH)₂, (CH₃OD)₂, (CD₃OH)₂, and (CD₃OH)₂. The preliminary analysis of the methyl internal rotation presented here was guided by the previously developed multidimensional tunneling theory which predicts 16 tunneling components for each R(J) transition from 25 distinct tunneling motions. Several isotopically mixed dimers of methanol have also been measured, namely ¹³CH₃OH, CH₃OD, CD₃OH, and CD₃OD bound to ¹²CH₃OH. Since the hydrogen bond interchange motion (which converts a donor into an acceptor) would produce a new and less favorable conformation from an energy viewpoint, it does not occur and only 10 tunneling components are observed for these mixed dimers. The structure of the complex is similar to that of water dimer with a hydrogen bond distance of 2.035 Å and a tilt of the acceptor methanol of 84° from the O-H-O axis. The effective barrier to internal rotation for the donor methyl group of (CH₃OH)₂ is ν₃ = 183.0 cm⁻¹ and is one-half of the value for the methanol monomer (370 cm⁻¹), while the barrier to internal rotation of the acceptor methyl group is 120 cm⁻¹.     

磁几何阻挫材料羟基氯化钴的中红外光谱特征

使用3种光谱仪测量了磁几何阻挫材料羟基氯化钴Co₂(OH)₃Cl的中红外(4000—400 cm^-1)吸收光谱,筛选出确信为Co₂(OH)₃Cl的本征吸收峰数据,结合已知的晶体结构参数,指认了官能团和指纹区相应谱峰的来源.在指认中着重探讨了羟基伸缩振动基频模vOH的具体实验数据,根据固体中氢键的特点,以Co₃—O平均距离为基准,推算了本样品 关键词： 红外光谱 几何阻挫 羟基氯化钴 三聚氢键     

Microstructured hydroxyl environments and Raman spectroscopy in selected basic transition-metal halides

Raman vibrational spectra of the selected basic (hydroxyl OH and deuteroxyl OD) transition-metal halides, geometrically frustrated material series α-, β-, γ-Cu₂(OH)₃Cl, α-Cu₂(OH)₃Br, β-Ni₂(OH)₃Cl, β-Co₂(OH)₃Cl, β-Co₂(OH)₃Br, γ-Cu₂(OD)₃Cl, and β-Co₂(OD)₃Cl are measured at room temperature and analysed to investigate the relationship between the microstructured OH environments and their respective Raman spectra. Among these selected samples, the last two are used to determine the OH stretching vibration region (3600 cm^-1—3300 cm^-1) and OH bending vibration region (1000 cm^-1—600 cm^-1) of OH systems in the spectra. Through the comparative analysis of the distances d(metal—O), d(O—halogen), and d(OH), the strong metal—O interaction and trimeric hydrogen bond (C_3v, C_s or C₁ symmetry) are found in every material, but both determine simultaneously an ultimate d(OH), and therefore an OH stretching vibration frequency. According to the approximately linear relationship between the OH stretching vibration frequency and d(OH), some unavailable d(OH) are guessed and some doubtful d(OH) are suggested to be corrected. In addition, it is demonstrated in brief that the OH bending vibration frequency is also of importance to check the more detailed crystal microstructure relating to the OH group.     

Rotational spectra, conformational structures, and dipole moments of thiodiglycol by jet-cooled FTMW and ab initio calculations

The rotational spectra of three low-energy conformers of thiodiglycol (TDG) (HOCH₂CH₂SCH₂CH₂OH) have been measured in a molecular beam using a pulsed-nozzle Fourier-transform microwave spectrometer. To determine the likely conformational structures with ab initio approach, conformational structures of 2-(ethylthio)ethanol (HOEES) (CH₃CH₂SCH₂CH₂OH) were used as starting points together with the consideration of possible intramolecular hydrogen bonding in TDG. Three lower-energy conformers have been found for TDG at the MP2=Full/6311G** level and ab initio results agree nicely with experimentally determined rotational constants. In addition, Stark measurements were performed for two of the three conformers for dipole moment determinations, adding to our confidence of the conformational structure matches between experimental observations and ab initio calculations. Of the three lower-energy conformers, one displays a compact folded-like structure with strong hydrogen bonding between the two hydroxyl groups and the central sulfide atom. Two other conformers have relatively open chain-like structures with hydrogen bonding between each of the hydroxyl groups to the central sulfur atom, of which one has pure b-type dipole moment according to the ab initio results.     

Structural studies of liquid alcohols by neutron diffraction

Neutron diffraction measurements have been made on methyl alcohol at room temperature for an incident wavelength of 0·94 Å. Cross sections have been obtained for CD₃OD, CD₃OH, and mixtures of these compounds. These data are subtracted to obtain the separated structure factors for intermolecular H₀H₀, the hydroxyl components, and the non-hydroxyl components. The Fourier transformations of the structure factors show components of both intra- and intermolecular distribution functions. Width parameters obtained from model fits are too large for thermal vibrations and are interpreted as geometrical broadening due to the stretching of bonds, variations in bond angles, and rotation of the methyl group. Differences in the real space distribution function between hydrogen and deuterium are noted.     

Rotational isomerism in 3-chloro-1-propanol from the microwave spectrum

The rotational spectra of two conformations of 3-chloro-propanol were observed for the four possible $\text{Cl(35)}\text{Cl(37)}$ and $\text{H}\text{D}$ isotopic species. For both conformations the oxygen atom is gauche with respect to the C₂C₃ bond and the hydroxyl hydrogen is trans with respect to the C₂C₁ bond. In one conformation (T) the chlorine is trans with respect to C₁C₂ and it is gauche in the other form (G). The ground state of the G form is about 0.7 kcal/mole more stable than that of the T form. A discussion is given about the failure to observe the H bond species. The most likely reason is the too close approach of Cl and O in this hypothetical configuration. The quadrupole coupling constants were obtained for the G form. The rotational spectra of five excited states of the T form and of one excited state of the G species were measured. Partial r₀ and r_s structures are given.     

HOD分子在?1B1态的光解动力学： 产物OH/OD的分支比以及OD键解离能

利用H(D)原子里德堡态时间飞渡谱技术研究了HOD超声射流分子束在124 nm附近的?态光解动力学．实验测量了HOD分子在?态的转动分辨的吸收谱,并得到了五个转动峰下H+OD以及D+OH通道的产物总的平动能谱．通过对产物平动能谱的分析,得到了?态解离产物OH和OD的分支比,并与Β态和?态相应解离产物的分支比做了对比．实验结果确定了HOD分子OD键的解离能为41751.3±5 cm^-1.     

Study of dynamics in pentachlorophenol in the solid state by 1D Nuclear Quadrupole Resonance exchange spectroscopy

The paper reports studies of the dynamic process in pentachlorophenol (PCP) in the solid state by one-dimensional Nuclear Quadrupole Resonance (NQR) exchange spectroscopy employing shaped rf pulses. Pentachlorophenol exhibits intramolecular hydrogen bonding between the hydroxyl proton and one of the o-chlorines. Reorientation of the hydrogen bond with migration of the hydroxyl proton from one o-chlorine to the other is possible in a wide temperature range. In this process the two o-chlorines are exchanged; at the same time this implies the exchange of the two m-chlorines as well, which we have chosen to monitor, modeling it as a two-site exchange process. A detailed analysis of the appropriate Bloch-McConnell equation is performed to formulate the relevant kinetic matrix. The exchange pulse sequence implemented by us involves suitably modulated shaped RF pulses to achieve simultaneous on-resonance excitation of the two exchanging sites. This approach results in a clear definition of the exchange time window and requires only a short experiment time. Kinetic parameters, namely, the spin-lattice relaxation rate and the exchange rate are deduced from the experimental signal intensities. Variable temperature measurements in the range 213 K–318 K have been carried out to extract the activation parameters as well.     

Conformation and hydrogen bond in 1,2-propanediol

The high-resolution microwave spectrum of two conformations, each with an internal hydrogen bond has been observed for the four possible $\text{H}\text{D}$ isotopic species of 1,2-propanediol. In both rotamers the hydroxyl in position 1 acts as proton donor to the oxygen in position 2, whose hydrogen is trans with respect to the C₁C₂ bond. In one case the methyl group is trans with respect to the C₁O₁ bond (T form) and in the other one is gauche (G form). The former is the more stable with ΔE_TG = ?0.58 kcal/mole. The dipole moment components have been obtained as: μ_a^T = 2.524, μ_b^T = 0.00, μ_c^T = 0.471, μ_a^G = 2.247, μ_b^G = 0.258, μ_c^G = 0.518 D. Evidence of the O ? O “shrinkage” upon deuteration has been observed as the r_s(HH) distances between the hydroxyl hydrogens are not consistent within the experimental errors with respect to the choice of the parent molecule. The spectra of some excited states have been measured for the T form.     

Raman and mid-infrared spectroscopic study of geometrically frustrated hydroxyl cobalt halides at room temperature

Mid-infrared absorption and Raman spectra of the geometrically frustrated material series,hydroxyl cobalt halides β-Co 2 (OH) 3 Cl and β-Co 2 (OH) 3 Br,are first,to the best of our knowledge,measured at room temperature,to study the corresponding relationship between their vibrational spectral properties and crystal microstructures.Through the comparative analysis of the four spectra we have categorically assigned the OH-related vibration modes of hydroxyl groups in the trimeric hydrogen bond environment (Co 3 ≡OH) 3… Cl/Br,and tentatively suggested vibration modes of O-Co-O,Co-O and Cl/Br-Co-Cl/Br units.These results can also become the basis for analysing their low-temperature spectral properties,which can help to understand the underlying physics of their exotic geometric frustration phenomena around phase transition temperatures.     

IR Spectroscopic Investigation and Conformational Analysis of Unsaturated C<Superscript>20</Superscript> and C<Superscript>22</Superscript> Steroid Alcohols

With the IR-spectroscopy method and the quantum-chemical AM1 method, the Δ²² and Δ²³ steroids containing a hydroxyl group at C²⁰ or C²² have been studied in order to elucidate the mutual arrangement in space of the hydroxyl group and of the double bond in the side chain of the molecules. The conformational analysis of steroid alcohols has been performed and the population of their stable conformers has been calculated. The frequencies of the bands in the IR spectra of alcohols in the region of the stretching vibration of OH groups have been assigned to certain conformers and the possibility of formation of the intramolecular hydrogen bond of the OH groups with the π-electron cloud of C=C bonds has been analyzed. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 317–324, May–June, 2005.     

Associative versus dissociative adsorption of water on Al(100)

The adsorption of water on Al (100) at 100 K has been studied using Fourier transform infrared-reflection absorption spectroscopy (FTIR-RAS), nuclear reaction analysis (NRA) and work function measurements (Δφ). All results are consistent with molecular adsorption, as no evidence was found for other possible dissociation products such as atomic O or D (H) at this temperature. By condensing alternating layers of D₂O and H₂O, it was found that a narrow feature in the _v(OD) (_v(OH)) region of the spectrum at 2720 cm⁻¹ (3700 cm⁻¹) is associated with non-hydrogen bonded OD (OH) groups in water molecules existing at the ice-vacuum interface. Surface hydroxyl groups resulting from dissociative adsorption exhibit a broader O-D stretch at 2760 cm⁻¹.     

How polar hydroxyl groups affect surface hydrophobicity on model talc surfaces

Based on molecular dynamics simulations, we have studied the wetting behaviors of water on the talc-like surface with different surface polarity by modifying the charge distribution of surface hydroxyl (–OH) groups. With the change of the charge of the hydrogen atom (denoted as δ_q) in –OH group, the contact angle decreases from 91° to 50° and then remains constant. On the surfaces with the larger charge of hydrogen atoms (δ_q ≥ 0.2 e), a water droplet is formed above a water monolayer, which is exactly contacted on the surface. Each water molecule in the monolayer forms one hydrogen bond (H bond) with surface –OH groups, without participating in any H bond with the water molecules within the monolayer or with the water molecules above the monolayer. The polarity of the –OH group also has a great influence on the dynamic behaviors of the interface water, such as residence time, hydrogen bond lifetime and self-diffusion coefficient. The diffusion of water molecules in the water monolayer near the highly polar surface is greatly suppressed, and the residence time of water molecules in the water monolayer even exceeds 12 ns.     

Exploring the reaction channels between arsine and the hydroxyl radical

The aim of this study was to present the reaction mechanism channels between arsine (AsH₃) and hydroxyl (OH) which was evaluated at CCSD(T)/CBS//CCSD/cc-pVTZ level. One potential channel is the hydrogen abstraction pathway (R1), leading to AsH₂ and H₂O products, which occurs due to the formation of an entrance complex (AsH₃OH) followed by a 1,2-hydrogen shift pathway (involving the proton transfer from the arsine group to hydroxyls, with one leading to the products). Additional channels are accessed via H-elimination pathways of the entrance complexes, forming arsinous acid (AsH₂OH; R2) and arsine oxide (AsH₃O; R3). In this respect, R2 is the only exoergic route of the three exit channels, representing the major branching ratio at 200–1000 K and, after 2000 K, R1 increases gradually becoming the major route of this reaction. In contrast, even at 4000 K, R3 is a highly unfeasible pathway. Therefore, the information predicted here provides new insights into the neutral–neutral chemical reaction dynamics regarding the Group V hydrides. On the other side, the R2 pathway may have some potential to solve the arsine oxidation puzzle as a possible primary pathway to the arsenic-oxygen species formation.     

Far infrared laser lines produced by methanol and its isotopic species: A review

Methanol (CH₃OH) is considered today one of the most important active media for the generation of laser radiation in the far-infrared (FIR) spectral region. Together with ten of its other isotopic species, it is responsible for the major part of the laser lines generated by the optical pumping technique. Due to the extreme importance of those molecules as laser generators, we understood that there was a necessity of a comprehensive work which would include as much pratical information as possible about each line.Chang et al⁽¹⁾ early recognized methanol as a source of strong FIR laser lines. Since then, more than 100 papers were published containing information about new laser emission. Recently, Moruzzi et al⁽¹¹⁴⁾ presented a review of 575 lines produced by¹²CH₃OH. In the present paper, we have extended the review to the various isotopic modifications of this molecule (namely¹³CH₃OH, CD₃OH,¹³CD₃OH, CD₃OD,¹³CD₃OD, CH₃OD, CH ₃ ¹⁸ OH, CH₂DOH, CH₂DOD and CHD₂OH), a total of nearly 2000 lines with wavelengths ranging from 19µm to 3030µm.     

H bonding of substituted pyridines on silica

The infrared spectra of a series of substituted pyridines which were adsorbed on silica have been obtained. A linear correlation is obtained between the wavenumber shift of the OH stretching fundamental of the surface hydroxyl groups towards lower wavenumber and the Hammett polar substituent parameter of the adsorbate. Deviations are only observed for tert.-butyl substituents in ortho-position and for ortho-substituents which render a dual interaction with neighbouring OH groups possible. The optical density of an IR continuous absorption is a function of the proton affinity of the adsorbate and it can be explained by assuming the formation of protonated adsorbed species which exhibit symmetrical NH⁺… N bond.     

Direct ab initio dynamics study of rate constants and kinetic isotope effects for C2(A3Π u ) + CH3OH reaction

The hydrogen abstraction of CH₃OH by C₂ (A³Π _u ) has been investigated by direct ab initio dynamics over a wide temperature range 200–3000?K. The potential energy surfaces (PESs) have been constructed at the UCCSD(T)/aug-cc-pVTZ//UMP2/6-311++G(d,p) levels of theory. Two different hydrogen abstractions on the methyl and hydroxyl sites of methanol are considered. For the methyl H-abstraction, it is essentially a hydrogen atom transfer (HAT), whereas the hydroxyl site H-abstraction is better described as a proton coupled electron transfer (PCET) according to the Natural Bond Orbital (NBO) analysis. The results suggest that the methyl site reaction is dominant, and the calculated rate constants are roughly consistent with available experimental values. On the other hand, the temperature dependence of deuterium kinetic isotope effects (KIEs) analysis reveals a substantial normal isotope effect in the methyl H-abstraction process, while normal and inverse KIEs coexist in the hydroxyl H-abstraction channel. Furthermore, the three and four–parameter expressions of Arrhenius rate constants are also provided within 200–3000?K.     

Hydrogen in the approximant <Emphasis Type="Italic">i</Emphasis>-TiZrHf: The energy state,charge, and diffusion

The energy of hydrogen dissolution in different tetrahedral pores of a 1/1 approximant of the icosahedral TiZrHf quasicrystal has been determined in terms of the density functional theory and ab initio pseudopotentials. At low and high degrees of loading of TiZrHf with hydrogen, the charges of atoms involved in the system and the Mayer bond order have been calculated for all possible M-M and M-H pairs. The diffusion coefficient of a single hydrogen atom in the system under study has been estimated numerically.