Rotation Of CH Research Articles

Microwave spectra, molecular geometries, and internal rotation of CH3 in N-methylimidazole⋯H2O and 2-methylimidazole⋯H2O Complexes.

Broadband microwave spectra have been recorded between 7.0 and 18.5 GHz for N-methylimidazole⋯H2O and 2-methylimidazole⋯H2O complexes. Each complex was generated by co-expansion of low concentrations of methylimidazole and H2O in argon buffer gas. The rotational spectra of five isotopologues of each complex have been assigned and analysed to determine rotational constants (A0, B0, C0), centrifugal distortion constants (DJ, DJK) and parameters that describe the internal rotation of the CH3 group. The results allow the determination of parameters in the (r0) molecular geometry of each complex. H2O is the hydrogen bond donor and the pyridinic nitrogen of imidazole is the hydrogen bond acceptor in each case. The ∠(O–Hb⋯N3) angles are 177(5)° and 166.3(28)° for N-methylimidazole⋯H2O and 2-methylimidazole⋯H2O respectively. These results are consistent with the presence of a weak electrostatic interaction between the oxygen atom of H2O and the hydrogen atom (or CH3 group) attached to the C2 carbon atom of imidazole, and with the results of density functional theory calculations. The (V3) barrier to internal rotation of the CH3 group within N-methylimidazole⋯H2O is essentially unchanged from the value of this parameter for the N-methylimidazole monomer. The same parameter is significantly higher for the 2-methylimidazole⋯H2O complex than for the 2-methylimidazole monomer as a consequence of the weak electrostatic interaction between the O atom and the CH3 group of 2-methylimidazole.

Rotation of CH3+ Cations in Helium Droplets.

Observation of the free rotation of molecules in helium droplets enabled microscopic study of interaction of quantum rotors with a superfluid environment at T = 0.4 K. This work extends studies of rotation in helium to molecular cations, such as methenium, CH3+. The spectrum of the v3 band of CH3+ around 3130 cm-1 has three prominent peaks assigned to the rotational structure of the band. While the free CH3+ is an oblate top, in helium it behaves as a prolate top. This effect is ascribed to the strong binding of two He atoms along the figure axis of the ion. Our results indicate that the other He atoms within the first solvation shell remain fluxional and in disparity with the widely accepted model of a rigid He "snowball" surrounding ions.

Microwave spectra and structures of 2-fluoro-4-picoline

Rotational spectrum of the ground state of 2-fluro-4-picoline has been investigated by pulsed jet Fourier transform microwave spectroscopy. Besides the parent species, all the mono-substituted 13C and 15N isotopologues in natural abundance have been also measured and assigned. The rotational spectrum displays the features of the quadrupole coupling effect of the 14N nucleus with a near-free internal rotation of CH3 top. The V3 barrier (191 (60) J/mol) to the internal rotation of CH3 has been estimated from the unexpected low values of the inertial defects.

LAR-CH: A Cluster-Head Rotation Approach for Sensor Networks

In wireless sensor networks, sensors are expected to work autonomously for a long time with a finite source of energy. Therefore, the sensors must be energy efficient in their duties to prolong the network lifetime. Cluster-based protocols are widely used in the literature to prolong the network lifetime. Clustering protocols use cluster-head rotation (CH-rotation) and re-clustering methods to rotate the energy-intensive load of CH nodes among other nodes of the network. Re-clustering is a global method, so its overhead cost is higher compared with CH-rotation. Existing clustering protocols employ an energy threshold on the residual energy of the CH for CH-rotation. This energy threshold can be static or dynamic. The static threshold does not consider the current energy load of the CH for CH-rotation. Thus, it increases premature death of CH nodes. In this paper, a load-aware rotation of CH (LAR-CH) approach is proposed, which sets a dynamic threshold for CH-rotation to reduce the premature death of CH nodes. The LAR-CH uses the current energy load of the CH to determine the dynamic threshold for CH-rotation. The simulation results show that LAR-CH reduces the premature death of CH nodes by 40% compared with the low-energy adaptive clustering hierarchy protocol.

Proton dynamics in tetramethylammonium cadmium chloride (CH3)4NCdCl3 single crystal by using 1H NMR measurements

Tetramethylammonium (TMA) cadmium chloride (TMCC), (CH3)4NCdCl3, has four phases with first-order transition temperatures at 104 and 118 K. To investigate the proton dynamics, we performed 1H nuclear magnetic resonance spectroscopy on a single TMCC crystal and measured the spin–lattice relaxation rate 1/T1 and rotating frame relaxation rate 1/T1ρ in the range of 65−300 K at 206.4 MHz under ∼4.8 T. 1/T1 displays an abrupt increase at 111.5 K and 1/T1ρ exhibits a sudden jump between 110 and 120 K. The discontinuities of both 1/T1 and 1/T1ρ across the phase transitions are unique in TMCC and have not been observed in other TMA-based compounds. Above 118 K, the temperature dependence of both T1 and T1ρ is linear, which indicates Arrhenius behavior. Below 118 K, T1 has a single minimum, and both T1 and T1ρ are linear in the low temperature range. This behavior at 206.4 MHz is very different from the double minima observed in T1 at 14.7 MHz for powder TMCC samples and in both T1 and T1ρ for other TMA-based compounds. By fitting two different regimes to the Bloembergen-Purcell-Pound curves, we extract both Ea and τ0 above and below 118 K. By carefully analyzing the T1 and T1ρ data, we ascertain that the coexistence of CH3 and TMA motions displays the double minima, unlike the T1 and T1ρ data at 206.4 MHz. Therefore, we conclude that the only active proton dynamics of TMCC originate from the CH3 rotation, and there is no reorientation of TMA ions, unlike other TMA-based compounds. Both T1 and T1ρ data confirm that the proton dynamics of the CH3 groups suddenly switch from rapid rotation above 118 K to slow rotation below 118 K, with no TMA ion dynamics in TMCC.

Proton-Coupled Electron Transfer to a Molybdenum Ethylene Complex Yields a β-Agostic Ethyl: Structure, Dynamics and Mechanism.

The interconversion of molybdenum ethylene and ethyl complexes by proton-coupled electron transfer (PCET) is described, an unusual transformation in organometallic chemistry. The cationic molybdenum ethylene complex [(PhTpy)(PPh2Me)2Mo(C2H4)][BArF24] ([1-C2H4]+; PhTpy = 4'-Ph-2,2',6',2″-terpyridine, ArF24 = [C6H3-3,5-(CF3)2]4) was synthesized, structurally characterized, and its electronic structure established by a combination of spectroscopic and computational methods. The overall electronic structure is best described as a molybdenum(III) complex with a metallacyclopropane and a redox neutral terpyridine ligand. Addition of the nonclassical ammine complex [(PhTpy)(PPh2Me)2Mo(NH3)][BArF24] ([1-NH3]+) to [1-C2H4]+ resulted in a net C-H bond-forming PCET reaction to yield the molybdenum ethyl [(PhTpy)(PPh2Me)2Mo(CH2CH3)][BArF24] ([1-CH2CH3]+) and amido [(PhTpy)(PPh2Me)2Mo(NH2)][BArF24] ([1-NH2]+) compounds. The reaction was reversed by addition of 2,4,6-tri tert-butylphenoxyl radical to [1-CH2CH3]+. The solid-state structure of [1-CH2CH3]+ established a β-agostic ethyl ligand that is maintained in solution as judged by variable temperature 1H and 13C NMR experiments. A combination of variable-temperature NMR experiments and isotopic labeling studies were used to probe the dynamics of [1-CH2CH3]+ and established restricted β-agostic -CH3 rotation at low temperature (Δ G‡ = 9.8 kcal mol-1 at -86 °C) as well as ethyl isomerization by β-hydride elimination-olefin rotation-reinsertion (Δ H‡ = 19.3 ± 0.6 kcal mol-1; Δ S‡ = 3.4 ± 1.7 cal mol-1 K-1). The β-(C-H) bond-dissociation free energy (BDFE) in [1-CH2CH3]+ was determined experimentally as 57 kcal mol-1 (THF) supported by a DFT-computed value of 52 kcal/mol-1 (gas phase). Comparison of p Ka and electrochemical data for the complexes [1-C2H4]+ and [1-NH3]+ in combination with a deuterium kinetic isotope effect ( kH/ kD) of 3.5(2) at 23 °C support a PCET process involving initial electron transfer followed by protonation leading to the formation of [1-CH2CH3]+ and [1-NH2]+ or a concerted pathway. The data presented herein provides a structural, thermochemical and mechanistic foundation for understanding the PCET reactivity of organometallic complexes with alkene and alkyl ligands.

Activation Energy of Organic Cation Rotation in CH3NH3PbI3 and CD3NH3PbI3: Quasi-Elastic Neutron Scattering Measurements and First-Principles Analysis Including Nuclear Quantum Effects.

The motion of CH3NH3+ cations in the low-temperature phase of the promising photovoltaic material methylammonium lead triiodide (CH3NH3PbI3) is investigated experimentally as well as theoretically, with a particular focus on the activation energy. Inelastic and quasi-elastic neutron scattering measurements reveal an activation energy of ∼48 meV. Through a combination of experiments and first-principles calculations, we attribute this activation energy to the relative rotation of CH3 against an NH3 group that stays bound to the inorganic cage. The inclusion of nuclear quantum effects through path integral molecular dynamics gives an activation energy of ∼42 meV, in good agreement with the neutron scattering experiments. For deuterated samples (CD3NH3PbI3), both theory and experiment observe a higher activation energy for the rotation of CD3 against NH3, which results from the smaller nuclear quantum effects in CD3. The rotation of the NH3 group, which is bound to the inorganic cage via strong hydrogen bonding, is unlikely to occur at low temperatures due to its high energy barrier of ∼120 meV.

Proton Spin-Lattice Relaxation in Organic Molecular Solids: Polymorphism and the Dependence on Sample Preparation.

We report solid-state nuclear magnetic resonance 1 H spin-lattice relaxation, single-crystal X-ray diffraction, powder X-ray diffraction, field emission scanning electron microscopy, and differential scanning calorimetry in solid samples of 2-ethylanthracene (EA) and 2-ethylanthraquinone (EAQ) that have been physically purified in different ways from the same commercial starting compounds. The solid-state 1 H spin-lattice relaxation is always non-exponential at high temperatures as expected when CH3 rotation is responsible for the relaxation. The 1 H spin-lattice relaxation experiments are very sensitive to the "several-molecule" (clusters) structure of these van der Waals molecular solids. In the three differently prepared samples of EAQ, the relaxation also becomes very non-exponential at low temperatures. This is very unusual and the decay of the nuclear magnetization can be fitted with both a stretched exponential and a double exponential. This unusual result correlates with the powder X-ray diffractometry results and suggests that the anomalous relaxation is due to crystallites of two (or more) different polymorphs (concomitant polymorphism).

Vibrational analysis, conformational stability, force constants, internal rotation barriers, MP2=full and DFT calculations of 1,3-dimethyluracil tautomers

The molecular structure of 1,3-dimethyluracil (C6H8N2O2; 1,3-DMU) is studied theoretically and experimentally using Gaussian 98 calculations and different spectroscopic techniques. The vibrational spectrum for 1,3-DMU in the solid phase is recorded in the IR range 4000-400 cm–1. Initially, in order to get the most stable structure, twelve structures were proposed for the titled compound as a result of the internal rotation of CH3 around C–N bonds and keto-enol tautomerism. The single point energy and frequency calculations are obtained by MP2 (Full) and DFT/B3LYP methods with the 6-31G(d) basis set using the Gaussian 98 computation package. After the complete relaxation of twelve isolated isomers, the (diketo) tautomer was the only favored structure owing to its low energy relative to the other isomers and the prediction of real frequencies. This interpretation is supported by the recorded infrared spectrum that shows the presence of only the diketo tautomer. Aided by the normal coordinate analysis and potential energy distributions, a confident vibrational assignment of the fundamental frequencies is calculated. The results are discussed herein and compared with similar molecules whenever possible.

α-Agostic Interactions and Growing Chain Orientation for Olefin Polymerization Catalysts

Growing chain orientational preference is one of the key factors determining the stereoselectivity of olefin polymerization and related reactions such as carboalumination; α-agostic interactions are an important component of this preference. Using insertion of ethene in the M–CH3 bond as a model, the intrinsic orientational preference was evaluated for a number of important catalyst types through determination of the energy profile for methyl group rotation at the insertion TS. Ti and Zr metallocenes show a pronounced preference (Ti, 10 kcal/mol; Zr, ∼6 kcal/mol) for a classical α-agostic arrangement with a single short M···CH contact and an elongated C–H bond; on CH3 rotation the agostic elongation mostly disappears. In contrast, for all non-metallocene systems studied the orientational preference is much smaller or even opposite that of metallocenes. Moreover, on CH3 rotation the agostic C–H bond elongation gets spread out over two C–H bonds rather than disappearing. These results point to greater chain...

Effect of different treatment on endophytic bacterial communities in continuous cropping of Chrysanthemum morifoliu

To reveal the effect of rotation cropping and bacterial manure on the growth of Chrysanthemum morifolium and screen the beneficial endophytic, the diversity of endophytic and dominant genera of different treatment groups were analyzed. Four different treatments were continuous cropping, rotation, self-made organic fertilizer and commercially available fertilizer, respectively. Endophytic bacterial diversity and dominant genera in different organs were examined using Terminal Restriction Fragment Length Polymorphism (T-RFLP). The results showed that enzyme Hae III was more appropriate than enzyme Hinfl because the number of TRFs digested by enzyme Hae III was more than that of enzyme Hinfl. In comparison of diversity, the endophytic bacterial communities' diversity index in group of cropping rotation and fertilizer was higher than that of continuous cropping which indicated that the addition of exogenous microorganism in soil could increase the diversity of plant endophyte. 18 dominant species were selected, including 3 kinds of Firmicutes, 4 kinds of Actinomycetes and 11 kinds of Proteobacteria. The results of dominant species comparison showed that the number of dominant species in continuous cropping of Ch. morifolium was significantly less than that of the rotation group. Some dominant bacteria in rotation group and fertilizer group such as Arthrobacter, Streptomyces, Streptomyces, Flavobacterium and Mycobacterium were not found in the continuous cropping of Ch. mortfolium group. Dominant species of fertilizer treatment group was similar with the rotation group, and the continuous cropping group's dominant species was more abundant. It indicates that these bacteria may be able to mitigate hindrance in continuous cropping, especially the Flavobacterium which can decompose the pathogenic fungi is worthy of further attention. Compared with leaves, there are more dominant species in roots and stems. The diversity of edophytic bacterial communities in continuous cropping of Ch. morifolium stays below than that in the rotation of Ch. morifolium, and fertilizer treatment can increase the diversity of continuous cropping so that it could mitigate hindrance in continuous cropping.

Substituent effect on geometric and electronic structure of benzenesulfonic acid: gas-phase electron diffraction and quantum chemical studies of 4-CH3C6H4SO3H and 3-NO2C6H4SO3H molecules

A combined gas-phase electron diffraction/mass-spectrometric and quantum chemical (B3LYP/cc-pVTZ, MP2/cc-pVTZ) study of the molecular structures of para-methylbenzenesulfonic acid (4-MBSA) and meta-nitrobenzenesulfonic acid (3-NBSA) was carried out. On the basis of mass spectrometric analysis, it was found that the substituted benzenesulfonic acids are thermostable at least up to 431(3) K. The fragmentations of 4-MBSA and 3-NBSA molecules under electron impact were analyzed. Quantum chemical calculations show that the 4-MBSA molecule exists as an enantiomeric pair, which is formed as a result of rotation of OH group about the S–O(H) bond. The 3-NBSA molecule has two conformers with different orientations of the O–H bond with respect to the nitro group and two corresponding enantiomers. The equilibrium configurations of 4-MBSA and both conformers of 3-NBSA have similar structures of the SO3H group, with the O–H bond eclipsing one of the S=O bonds. Selected experimental bond distances for 4-MBSA/3-NBSA are (A) rh1(C–C)av = 1.403(3)/1.395(4); rh1(C–S) = 1.765(5)/1.784(5); rh1(S=O)av = 1.433(4)/1.438(4); and rh1(S–O) = 1.618(4)/1.620(4). The potential functions for the internal rotation of SO3H, OH, and CH3 or NO2 groups were calculated, and the transition states between enantiomers (conformers) were determined. The influence of substituent's nature on molecular geometry as well as on the energies of frontier orbitals and red-ox properties of the compounds is discussed. The inductive and mesomeric substituent effects were estimated from the donor–acceptor interaction energies of the natural bond orbitals of substituent and benzene frame. The correlation between group electronegativities and cooperative energetic characteristics of inductive and mesomeric effects of substituents is shown.

Rotational and Translational Dynamics of N-Butyl-N-methylpiperidinium Trifluoromethanesulfonimide Ionic Liquids Studied by NMR and MD Simulations

Translational and rotational dynamics of the room temperature ionic liquid N-butyl-N-methylpiperidinium trifluoromethanesulfonimide, [C4mpip][Tf2N], were investigated by 1H, 19F, and 13C nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) simulation. 1H NMR and MD results for the temperature-dependent diffusion coefficients, D, spin–lattice relaxation times, T1, and rotational correlation times, τc, for each site in the cation of [C4mpip][Tf2N] are in good agreement. The T1 data indicate a long N–CH3 group rotation time, comparable to the overall molecular reorientation time. Correlation time comparisons between 1-butyl-3-methylimidazolium RTILs with different anions (Cl–, PF6–, Tf2N–) argue against invoking hydrogen bond interactions between the N–CH3 hydrogens and the electron rich center of the anion as an explanation of the long N–CH3 rotation times. Correlation time comparisons between piperidinium and pyrrolidinium RTILs with a common anion (Tf2N–) suggest that correlation time...

Rotational and Translational Dynamics of Rhodamine 6G in a Pyrrolidinium Ionic Liquid: A Combined Time-Resolved Fluorescence Anisotropy Decay and NMR Study

NMR spectroscopy and time-resolved fluorescence anisotropy decay (TRFAD) are two of the most commonly used methods to study solute-solvent interactions. However, only a few studies have been reported to date using a combined NMR and TRFAD approach to systematically investigate the overall picture of diffusional and rotational dynamics of both the solute and solvent. In this paper, we combined NMR and TRFAD to probe fluorescent rhodamine dye in a pyrrolidinium-based room temperature ionic liquid (RTIL), an emergent environmentally friendly solvent type used in several energy-related applications. A specific interaction of the R6G cation and [Tf2N] anion was identified, resulting in near-stick boundary condition rotation of R6G in this RTIL. The diffusional rates of the R6G solute and [C4mpyr][Tf2N] solvent derived from (1)H NMR suggest the rates are proportional to their corresponding hydrodynamic radii. The (1)H and (13)C NMR studies of self-rotational dynamics of [C4mpyr][Tf2N] showed that the self-rotational correlation time of [C4mpyr](+) is 47 ± 2 ps at 300 K. At the same temperature, we find that the correlation time for N-CH3 rotation in [C4mpyr](+) is 77 ± 2 ps, comparable to overall molecular reorientation. This slow motion is attributed to properties of the cation structure.

Mid-infrared spectra of methane dispersed in solid neon and argon

We have recorded, in absorption, infrared spectra of samples of methane, CH 4 and CD 4, dispersed at molar fraction 0.0001–0.005 in solid neon, in solid argon and in their equimolar solid mixture in the temperature range 3–21 K and in the spectral domain 5000–500 cm −1 at resolution 0.04–0.2 cm −1. We undertook quantitative fitting of the spectral profiles with components of gaussian and lorentzian shapes. Comparison of our spectra in regions of fundamental modes both ν 3 and ν 4 with published spectra of CH 4 and CD 4 in either crystalline para-dihydrogen or droplets of liquid helium indicates evidence for hindered rotation of CH 4 molecules in Ar but not for rotation of CH 4 or CD 4 in Ne or in a mixture of Ne and Ar. For CD 4 in solid Ar, the evidence for even hindered rotation is ambiguous. We make new assignments of lines to 13CH 4 and 13CD 4 in their environments in solid Ne and Ar.

A quantum chemical study of the structure and energy of β-diketonates. XVII. Internal rotation of radical substituents in β-diketonate molecules

A quantum chemical study of the internal rotation of CX3 (X = H, F, CH3) radical substituents in scandium and calcium β-diketonate complexes is performed. Calculations are carried out using the GAUSSIAN-03 program at the HF and DFT/B3LYP levels with relativistic effective core pseudo-potentials and valence double zeta basis sets. Analytical expressions V(φ) are obtained that describe the potential energy variation during the rotation of CX3 groups. The rotation of CH3 and CF3 groups is shown to be described by a simple potential of the form V = V0/2 + V3cos(3φ), while for the description of the rotation of tert-butyl groups it is required to use a more complex function V = V0/2 + V3cos(3φ) + V6cos(6φ). Based on the obtained expressions for V(φ), the effective torsion angles φef of the rotation of CX3 groups are calculated for different temperatures. It is shown that φef obtained based on the quantum chemical calculations are close to the values obtained in electron diffraction experiments.

Advances in Use of p‐H2 as a Novel Host for Matrix IR Spectroscopy

AbstractA review of recent advances in IR spectroscopy using p‐H2 as a matrix host in our laboratory is presented. The softness of this novel p‐H2 matrix host not only makes high‐resolution spectroscopy feasible but also provides new applications. Molecular motion, such as the rotation of C2H4, internal rotation (torsion) of CH3OH, and rotation of CH3F about a single axis are characterized in this p‐H2 matrix. In contrast, no evidence for rotation of CH3I and CH3 was found. The diminution of the cage effect leads to the possibility of production of free radicals via either photolysis in situ or bimolecular reactions of molecules with atoms that are produced in situ from their molecular precursors. Taking advantage of these unique features, we identified the IR spectrum of CH3 produced from photolysis of CH3I and CH3S produced from photolysis of CH3SCH3 and CH3SSCH3. The reaction of Cl with CS2 in solid p‐H2 yields ClSCS instead of ClCS2. The reaction of Cl with HCOOH in solid p‐H2 yields only a complex, Cl·HCOOH, not HCl and HOCO. The presence of o‐H2 in trace proportions turned out to be an important factor in the interpretation of IR spectra of species embedded in solid p‐H2. Experimental techniques to minimize the amount of o‐H2 and to characterize its relative concentration with spectra of H2O·o‐H2 are discussed.

Chirality of and gear motion in isopropyl methyl sulfide: A Fourier transform microwave study

Isopropyl methyl sulfide (CH(3))(2)CHSCH(3) was investigated by Fourier transform microwave spectroscopy. Two rotational isomers gauche and trans were detected. The rotational spectra of gauche were found fit to an asymmetric rotor pattern, except for being split by the internal rotation of CH(3) attached to S with the potential barrier V(3) of 601.642 (65) cm(-1) and for exhibiting the effect of tunneling between the two equivalent gauche forms in a few high-K transitions. The tunneling was discussed from a viewpoint of chirality. The trans spectra appeared generally similar to those of gauche, with V(3) to the S-CH(3) internal rotation of 559.00 (11) cm(-1), but satellite lines accompanied the ground torsional state lines in some high-K transitions. These satellites were ascribed to the excited state of the C(isop)-S torsion. In fact, the potential function for this torsion was shown by an ab initio calculation to be flat or even of double minima around the trans position, which was presumably caused by a gear coupling between the two methyl groups of the isopropyl group and the one in the S-CH(3).

CH3 Internal Rotation in the S0 and S1 States of 9-Methylanthracene

Fluorescence excitation spectra and dispersed fluorescence spectra of jet-cooled 9-methylanthracene-h12 and -d12 (9MA-h12 and 9MA-d12) have been observed, and the energy levels of methyl internal rotation (CH3 torsion) in the S0 and S1 states have been analyzed. The molecular symmetry of 9MA is the same as that of toluene (G12). Because of two-fold symmetry in the pi system, the potential curve has six-fold barriers to CH3 rotation. In toluene, the barrier height to CH3 rotation V6 is very small, nearly free rotation. As for 9MA-h12, we could fit the level energies by potential curves with the barrier heights of V6(S0) = 118 cm(-1) and V6(S1) = 33 cm(-1). These barrier heights are remarkably larger than those of toluene and are attributed to hyperconjugation between the pi orbitals and methyl group. The dispersed fluorescence spectrum showed broad emission for the excitation of 0(0)(0) + 386 cm(-1) band, indicating that intramolecular vibrational redistribution efficiently occurs, even in the vibronic level of low excess energy of the isolated 9MA molecule.

NMR Studies on Effects of Temperature, Pressure, and Fluorination on Structures and Dynamics of Alcohols in Liquid and Supercritical States

We measured 1H NMR chemical shifts (delta H) and 1H and 2H NMR spin-lattice relaxation times (1H- and 2H-T1) of methanol, ethanol, 2-propanol, 2,2,2-trifluoroethanol, and 1,1,1,3,3,3-hexafluoro-2-propanol in the temperature range from 298 to 673 K at reduced pressures ( Pr = P/ Pc) of 1.22 and 3.14. The delta H values showed that the degree (X HB) of hydrogen bonding decreased in the order of methanol > ethanol >2-propanol > H2O, and that the hydrogen bonding was much affected by fluorination, because of the intramolecular H-F interactions in supercritical (sc) states. Moreover, 1H- T 1 measurements revealed that the relaxation processes of OH groups in nonfluoroalcohols are controlled by dipole-dipole (DD) and spin-rotation (SR) mechanisms below and above the critical temperature (Tc), while the cross-correlation effects connected with intramolecular DD interactions between a carbon atom and an adjacent proton played an important role for hydrocarbon groups (CHn, n = 1-3) under sc conditions. This interpretation was also supported by two other results. The first is that the intramolecular H-F interactions strongly inhibit the internal rotation of CH and CH2 groups of sc fluoroalcohols, and the second is that the molecular reorientational correlation times (tauc(D)) obtained from 2H- T 1 values of deuterated hydrocarbon groups (CDn ) at temperatures above T c have significantly less temperature dependence than those of OD groups. Actually, the apparent activation energy (DeltaEa) for molecular reorientational motions in sc alcohols was smaller compared with liquid alcohols, being about 1 order of magnitude.