New Mechanism for the Broadening of the Hydrogen Stretching Peak on Hydrogen Bonding

Two-bond, carbon-proton coupling in halogenated ethylenes

“…bond coupling in m-disubstituted compounds with arrangement 4 is interpretable as the result of the large and positive substituent effects arising from structures 1 and 3 so that a large, positive two-bond coupling would be expected (and is observed). On the other hand, the trans isomers (5) would have contributions of types 2…”

“…Changes in bond angles and/or long-range s-bond order or orbital-orbital polarizability effects may account for part or all of the small deviations from additivity, but it seems clear the major influence on the twobond coupling can be rationalized by additivity of substituent effects in the monosubstituted compounds. 5 The remaining problem is how to interpret the couplings in the monosubstituted vinyl compounds themselves. The two-bond, carbon-proton coupling in situations like 3 may be understood in terms of the molecular orbital theory developed by Pople and Bothner-By for proton-proton coupling.6 A positive substituent effect was shown to be associated with the withdrawal of electrons from the -CH2fragment by an electronegative substituent.…”

A Global Analytical Representation of the Potential Energy Surface of the FHF– Anion

“…For more than half a century, this system has been the subject of a large number of experimental ,− and theoretical − ,− studies; this list is not complete, the reader may find additional references in the cited work. Experimental thermodynamic studies ,, of the binding energy along the path of reaction , yielded reaction enthalpies ranging between 35 and 60 kcal mol –1 (1 kcal = 4.184 kJ).…”

“…The unusual nature of its bonding has made it an interesting system for numerous vibrational spectroscopic, infrared (IR), and Raman studies in sodium or potassium crystals, − in matrix isolation, , and in the gas phase. ,, The best experimental spectroscopic study so far of FHF – and FDF – was provided by Kawaguchi and Hirota using IR diode laser spectroscopy in conjunction with the magnetic field modulation technique and led to the conclusive assignment of the three fundamental as well as of two combination bands. The lowest energy vibrational mode in FHF – , ν̃ 1 = 583.0539(13) cm –1 , has been assigned to the symmetric stretching motion.…”

IR Spectrum of FHF– and FDF– Revisited Using a Spectral Method in Four Dimensions

“…The bifluoride ion (FHF – ) is the simplest representative of the hydrogen bihalides XHY – (X, Y = F, Cl, Br, or I), a family of compounds well characterized experimentally − as well as theoretically. − The ongoing interest in FHF – arises from the fact that it presents one of the strongest hydrogen bonds known. For the dissociation of the hydrogen bond toward F – –HF, energies ( D 0 ) of up to ca.…”