Vibrational Properties of the Isotopomers of the Water Dimer Derived from Experiment and Computations

Abstract

The water dimer and its 11 deuterated isotopomers are investigated utilizing coupled cluster theory and experimental data as input for a perturbational determination of the isotopomer frequencies. Deuterium substitution reduces the H-bond stretching frequency by maximally 12 cm À1 from 143 to 131 cm À1 , which makes a spectroscopic differentiation of H-and D-bonds difficult. However, utilizing the 132 frequencies obtained in this work, the identification of all isotopomers is straightforward. The CCSD(T)/CBS value of the binding energy D e is 5.00 kcal mol À1 . The binding energy D 0 of the water dimer increases upon deuterium substitution from 3.28 to maximally 3.71 kcal mol À1 reflecting a decrease in the zero point energy contribution. The entropy values of the D-isotopomers increase from 73 to 77 entropy units in line with the general observation that a mass increase leads to larger entropies. All 12 isotopomers possess positive free binding energies at 80 K and a reduced pressure of 110 Pa, which means that they can be spectroscopically observed under these conditions.

Decoding chemical information from vibrational spectroscopy data: Local vibrational mode theory

“…Based on a fruitful combination of quantum chemical predictions and experimental realization, for the first time, nonclassical H‐bonding involving a BH⋯ π interaction could be identified 268,269 . According to the Cremer–Kraka criteria for covalent bonding, 294,295 this interaction is electrostatic in nature with a BSO n of 0.35, being comparable to what we found for the H‐bond in the water dimer 174,250 …”

“…268,269 According to the Cremer-Kraka criteria for covalent bonding, 294,295 this interaction is electrostatic in nature with a BSO n of 0.35, comparable to what we found for the H-bond in the water dimer. 174,250 A method for the quantitative assessment of aromaticity and anti-aromaticity based on vibrational spectroscopy was developed, 270 which led to a new understanding of Clar's rule. 296 The analysis of 30 mono-and polycyclic conjugated hydrocarbons confirmed Clar's rule of disjoint benzene units in many cases, but corrects it in those cases where peripheral pi-delocalization leads to higher stability.…”

Re‐evaluation of the bond length–bond strength rule: The stronger bond is not always the shorter bond

“…[29][30][31] The usefulness of the local vibrational mode description of the bond strength has been documented by the characterization of CC bonds, [29,[32][33][34] NN bonds, [35] CO bonds, [36] CX bonds with X 5 F, Cl, Br, I, [37][38][39][40] H-bonding, [41][42][43][44] pnicogen bonding, [45,46] and the characterization of isotopomers. [47] The main objectives of this work are (i) to critically reevaluate previously published reverse BLBS relationships, (ii) to introduce reliable bond strength orders (BSOs) needed for characterizing unusual bonds, (iii) to elucidate the interplay of electronic and electrostatic factors determining the stability of electron-rich bonds, and (iv) to derive a rational for any deviation from the commonly known inverse BLBS relationships.…”

“…The preferred tool in this work will be a dynamical model of the bond strength based on vibrational spectroscopy and the theory of local modes, which was introduced by Konkoli and Cremer and which, since then, has been proved to be physically sound, generally applicable, and a direct way of determining the intrinsic strength of a bond . The usefulness of the local vibrational mode description of the bond strength has been documented by the characterization of CC bonds, NN bonds, CO bonds, CX bonds with X = F, Cl, Br, I, H‐bonding, pnicogen bonding, and the characterization of isotopomers …”

6th Heron Island Conference on Reactive Intermediates and Unusual Molecules

“…pyridine-palladacycles (G. J. Rowlands et al), [5] benzonitrile oxide cycloadditions (G. P. Savage and C. Francis), [6] adamantanethione reactions (N. Drinnan and C. Wentrup), [7] dyesensitised solar cells (E. Brunet et al), [8] iron complexes (P. Comba et al), [9] boric acid catalysed esterification (T. A. Houston et al), [10] amidinium tetrazolide (A. J. Arduengo et al), [11] use of Otera's catalyst (C. A. Hutton et al), [12] methyltriacetylene cation (J. P. Maier et al), [13] retro-Mannich cascade rearrangement (P. Wipf et al), [14] computations on water dimers (E. Kraka et al), [15] cyclopropane radical cation (W. Zou and D. Cremer), [16] nitrile selenides (T. Pasinszki et al), [17] polarization in a halogen bond (T. Clark et al), [18] triazenes (S. Bräse et al), [19] sydnone photochemistry (C. Wentrup et al), [20] dihydroazulene photoswitches (M. B. Nielsen et al), [21] isocyanide-NHC-platinum(II) complexes (A. S. K. Hashmi et al), [22] benzynes (T. Ikawa et al), [23] gold catalysis (A. S. K. Hashmi et al), [24,25] HERON reaction of dialkoxyamides (S. A. Glover et al), [26] silylated enoldiazoacetates (M. P. Doyle et al), [27] and microflow photochemistry (M. Oelgemöller et al). [28] The lively late-afternoon poster sessions on the patio with a view of the sunset and reef sea life (including whales on occasion) are a recurring and unforgettable part of the Heron Island Conferences (Fig.…”