A shortening of the C-H bond lengths and a blue shift stretching frequencies for C-F small middle dot dotH-C groups indicates that anti-hydrogen bonds are present difluoromethane dimer. The most stable conformer has three such interactions (shown schematically).

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTGas-phase tautomeric equilibrium of 2-pyridinone and 2-hydroxypyridine by microwave spectroscopyL. D. Hatherley, R. Brown, P. Godfrey, A. Pierlot, W. Caminati, Damiani, S. Melandri, L. B. FaveroCite this: J. Phys. Chem. 1993, 97, 1, 46–51Publication Date (Print):January 1993Publication History Published online1 May 2002Published inissue 1 January 1993https://pubs.acs.org/doi/10.1021/j100103a011https://doi.org/10.1021/j100103a011research-articleACS...

Abstract A gas‐phase nitrogen–nitrogen noncovalent interaction has been unveiled in the nitroethane–trimethylamine complex an environment free from solvent and matrix effects using rotational spectroscopy supersonic expansion. Different quantum chemical models (NOCV/CD NBO) agree indicating that this largely prevails over C−H⋅⋅⋅O C−H⋅⋅⋅N hydrogen bonds. Furthermore, a SAPT analysis shows electrostatic dispersion interactions play comparable role stabilizing complex. The conformational...

Recently reported rotational spectroscopic studies on small dimers and oligomers bound by weak hydrogen bonds show that the driving forces, spatial arrangement dynamical features displayed are very different from those involved in stronger conventional bonds. The binding energies (similar to of van der Waals interactions) imply stabilization dimer is often obtained networks Even presence multiple partner molecules a high degree internal freedom within complex. This paper analyses several...

The supersonic molecular beam (absorption millimeter wave and microwave Fourier transform) spectra of the 1:1 complex between pyrimidine four isotopomers water (H2O, HDO, D2O, H218O) have been assigned. derived moments inertia are consistent with a planar (or nearly planar) structure adduct in which one hydrogen molecule is bound to nitrogen aromatic ring, “free” entgegen ring. Only high level ab initio calculations (6-31G**+MP2-BSSE) account for coplanarity ring molecule. bond stretching...

The free jet millimeter wave spectra of four isotopomers the 1:1 complex between difluoromethane and water have been observed assigned. molecule lies in FCF plane difluoromethane, linked through an O−H···F hydrogen bond to one fluorine atom, entgegen second one. H parameters are r(F···H) = 2.20 Å, ∠(F···H−O) ≅ 135°, ∠(C−F···H) 93°, respectively. oxygen is zusammen C "free" moiety. value 90° C−F···H angle indicative preservation p character lone pairs adduct.

The rotational spectra of two isotopologues (CF3(35)Cl-CO and CF3(37)Cl-CO) the CF3Cl-CO adduct have been investigated analyzed using supersonic-jet Fourier transform microwave spectroscopy, found to features a symmetric top. Rotational, centrifugal distortion, nuclear quadrupole ((35)Cl (37)Cl) coupling constants precisely obtained from high-resolution measurements. subunits complex are held together via ClC halogen bond interaction. Information on internal dynamics dissociation energy is provided.

Completely planar is the hydrogen-bonded complex of pyrazine and water (see sketch), which was obtained by supersonic expansion investigated rotational spectroscopy. The molecule lies in plane aromatic ring, lone pair electrons on nitrogen atom functions as acceptor N⋅⋅⋅H–O hydrogen bond, not—as corresponding benzene complex—the π electrons.

The rotational spectrum of the weakly bound complex pentafluoropyridine·water has been investigated with pulsed jet Fourier transform microwave spectroscopy. From analysis parameters parent species and three water isotopologues, structural arrangement adduct unambiguously established. results show that full ring fluorination pyridine a dramatic effect on its binding properties: It inverts electron density distribution above ring, creating π-hole, respect to typical π-cloud benzene pyridine....

Calcitonin (CT) inhibits osteoclastic bone resorption and induces calcium uptake from body fluids. A comparative study of the conformational behaviours therapeutic calcitonins [salmon (s), eel (e), a synthetic calcitonin analogue (Elcatonin), porcine (p) human (h) calcitonins] as function solvent polarity temperature have been performed by circular dichroism spectroscopy. Elements secondary structure were lacking in H 2 O but could be observed 2,2,2‐trifluoroethanol sodium dodecyl sulphate....

The trimer of difluoromethane, (CH2F2)3, has been characterized by supersonic jet Fourier transform microwave spectroscopy. rotational spectrum displays all types (μa, μb, and μc) transitions, showing that the adduct does not possess any element molecular symmetry. investigation three 13C species in natural abundance indicates carbon atoms form a triangle where C−C distances are 3.648(2), 3.825(8), 3.942(6) Å, respectively. subunits held together nine CH···F weak hydrogen bonds.

The keto−enol tautomerism of 4-hydroxypyrimidine and the related molecules S-methyl-2-thiouracil 2-thiouracil has been investigated using synchrotron-based techniques. populations constituent tautomers thermodynamic parameters have obtained by analysis core-level photoemission spectra. effect substituents on stability revealed. Attaching additional OH (or SH) groups to aromatic ring stabilizes dioxo oxo-thione) forms. However, substitution hydrogen in position 2 an S-CH3 group (that is,...

The topology of the interaction water with benzene changes drastically upon full H→F substitution on aromatic ring: weak O-H⋅⋅⋅π hydrogen bond is replaced by a O⋅⋅⋅π linkage, about same strength. Hexafluorobenzene-water appears to be prototype system investigate this kind bond. pulsed Fourier transform microwave technique has been used for detection rotational spectra normal species and five isotopologues which unambiguously led identification geometry. Quantum mechanical calculations have...

The rotational spectra of the 1:1 formic acid-carbon dioxide molecular complex and its monodeuterated isotopologues are analysed in 6.5-18.5 59.6-74.4 GHz frequency ranges using a pulsed jet Fourier transform microwave spectrometer free-jet absorption millimetre wave spectrometer, respectively. Precise values quartic centrifugal distortion constants obtained from measured frequencies, quadrupole coupling determined deuterium hyperfine splittings. Structural parameters estimated moments...

The rotational spectrum of jet-cooled tetrahydrofuran has been investigated in the 8–18 and 60–78 GHz frequency ranges. Only four lowest vibrational levels remain populated jet conditions. Two pseudorotation spacings have measured directly to be ΔE01=21 307.71(3) MHz ΔE23=61 205.69(3) MHz. They used, together with 10 far infrared transition frequencies effective moments inertia ground state their shifts upon excitation observed this work, determine potential energy function for associated...

All change: The dynamics, location, and hydrogen-bond features of CHF3 change drastically on going from the benzene–CHF3 to pyridine–CHF3 molecular adduct. barrier internal rotation increases almost nothing ≈0.6 kJ mol−1; moiety moves into ring plane above, a CH⋅⋅⋅N linkage replaces CH⋅⋅⋅π contact (see figure).

The free jet millimeter-wave absorption spectrum of 1,3-cyclohexanedione has been investigated in the 59.6-74.4 GHz frequency range, and rotational spectra two conformational species, chair-diketo boat-diketo, probably one excited vibrational state belonging to form have assigned. Quantum chemical calculations, performed at B3LYP/6-311++G** MP2/6-311++G** levels, were used characterize potential energy surface minima. related interconversion observed diketonic species was modeled DFT level.

The weakly bound 1:1 complex between acrylonitrile (CH2═CHCN) and water has been characterized spectroscopically in the millimeter wave range (59.6-74.4 GHz) using a Free Jet Absorption Millimeter Wave spectrometer. Precise values of rotational quartic centrifugal distortion constants have obtained from measured frequencies normal isotopically substituted moiety (DOH, DOD, H(18)OH). Structural parameters estimated their differences among isotopologues: planar structure with two subunits held...