Sonia Melandri

Bio: Sonia Melandri is an academic researcher from University of Bologna. The author has contributed to research in topics: Rotational spectroscopy & Hydrogen bond. The author has an hindex of 27, co-authored 148 publications receiving 2742 citations. Previous affiliations of Sonia Melandri include Monash University, Clayton campus & University of Coimbra.

The C‐F⋅⋅⋅H‐C “Anti‐Hydrogen Bond” in the Gas Phase: Microwave Structure of the Difluoromethane Dimer

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

Gas-phase tautomeric equilibrium of 2-pyridinone and 2-hydroxypyridine by microwave spectroscopy

Abstract: The tautomerism of 2-hydroxypyridine/2-pyridinone has been investigated by microwave spectroscopy using both a conventional spectrometer and also a jet-cooled millimeter-wave spectrometer. We have observed spectra attributable to both the (Z)-hydroxy tautomer and the pyridinone tautomer and also their monodeutero isotopomers, the relative abundances in both spectrometers being about 3: 1 in favor of the hydroxy form. From relative intensity and dipole moment measurements, we estimate the energy difference between the vibrational ground states of the two tautomers to be ΔE 0,0 =270 (30) cm -1

The hydrogen bond between water and aromatic bases of biological interest: An experimental and theoretical study of the 1 : 1 complex of pyrimidine with water

Abstract: The supersonic molecular beam (absorption millimeter wave and microwave Fourier transform) spectra of the 1:1 complex between pyrimidine and four isotopomers of water (H2O, HDO, D2O, and H218O) hav...

A new criterion for the determination of molecular structures from ground state rotational constants

Abstract: Kraitchman has shown that a single isotopic substitution on an atom is sufficient to determine directly the coordinates of that atom with respect to the principal axes of the original molecule. Kraitchman's formulas represent exact solutions of the equations for the equilibrium moments of inertia. However, the effects of the zero‐point vibrations are such that the coordinates obtained by substitution from the ground state moments of inertia I0 are systematically less than r0. These coordinates have here been called r (substitution) or rs, and it is found that rs≃(r0+re)/2, and Is= ∑ imirsi2≃(I0+Ie)/2.In the usual method of solution, the coordinate of one atom is determined from the equation for I0, and therefore the difference I0—Is must be made up by this one coordinate. This introduces a large error in the structures normally determined from ground state constants, and results in variations of 0.01 A in structures determined from different sets of isotopic species. If instead, we obtain the structure on...

Red-, blue-, or no-shift in hydrogen bonds: a unified explanation.

Abstract: We provide a simple explanation for X-H bond contraction and the associated blue shift and decrease of intensity in IR spectrum of the so-called improper hydrogen bonds This explanation organizes hydrogen bonds (HBs) with a seemingly random relationship between the X-H bond length (and IR frequency and its intensity) to its interaction energy The factors which affect the X-H bond in all X-H [midline ellipsis] Y HBs can be divided into two parts: (a) The electron affinity of X causes a net gain of electron density at the X-H bond region in the presence of Y and encourages an X-H bond contraction (b) The well understood attractive interaction between the positive H and electron rich Y forces an X-H bond elongation For electron rich, highly polar X-H bonds (proper HB donors) the latter almost always dominates and results in X-H bond elongation, whereas for less polar, electron poor X-H bonds (pro-improper HB donors) the effect of the former is noticeable if Y is not a very strong HB acceptor Although both the above factors increase with increasing HB acceptor ability of Y, the shortening effect dominates over a range of Ys for suitable pro-improper X-Hs resulting in a surprising trend of decreasing X-H bond length with increasing HB acceptor ability The observed frequency and intensity variations follow naturally The possibility of HBs which do not show any IR frequency change in the X-H stretching mode also directly follows from this explanation

Fluorinated liquid crystals – properties and applications

Abstract: This critical review begins with a brief, but essential, introduction to the special nature of liquid crystal materials, their peculiar properties, and their commercial applications, followed by an introductory insight into the remarkable nature of the fluoro substituent, and its fascinating influence on the properties of organic compounds. However, the main focus of the review is to discuss the enormous amount of exciting research on fluorinated liquid crystals that has been reported. The small size of the fluoro substituent enables its incorporation into all types of liquid crystal, including calamitic, discotic, banana, lyotropic, and polymers, without ruining the liquid crystalline nature of the material. However the fluoro substituent is larger than hydrogen, and hence causes a significant steric effect, which combined with the high polarity, confers many fascinating, and often remarkable, modifications to melting point, mesophase morphology and transition temperatures, and the many other very important physical properties, such as dielectric anisotropy, optical anisotropy, and visco-elastic properties. There are many different positions within a liquid crystal structure where a fluoro substituent can be located, including (i) a terminal position, (ii) within a terminal chain, as a semi-fluorinated or as a perfluorinated chain, or as one fluoro substituent at a chiral centre, (iii) as part of a linking group, and (iv) a lateral position in the core section. Such variety enables the interesting and advantageous tailoring of properties, both for the fundamental purposes of establishing structure–property relationships, and for materials targeted towards commercially-successful liquid crystal display applications.