Zilberg, Shmuel and Dick, Bernhard (2017) Less stable tautomers form stronger hydrogen bonds: the case of water complexes. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 19 (36). pp. 25086-25094. ISSN 1463-9076, 1463-9084
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Hydrogen bonding in cyclic complexes of water with tautomeric pairs of molecules M-0 and M-1 is calculated to be stronger by more than 25% for the less stable tautomer M1 in all cases where the energy gap between the two tautomers is large (Delta E(M-0 - M-1) 4 10 kcal mol(-1)). This is accompanied by a large red-shift (4200 cm(-1)) of the N-H/O-Hstretch frequency in the complexes involving M1. Large barriers for double proton transfer in both directions should permit an experimental verification. Exceptions to this rule were found in heterocycles with an N-C=O fragment incorporated into a conjugated cycle resulting in two nearly degenerate tautomers - keto and enol forms. The wavefunction of the keto form has a large contribution from a zwitterionic VB structure which is also aromatic. This increases the polarity of the keto group, making the oxygen atom a strong H-bond acceptor. It can also stabilize the keto form below the aromatic enol form. In this case the extra-HB stabilization is observed for the most stable tautomer (i.e. for the keto form). H-bonding enhances the aromatic character of less aromatic molecules, but the more aromatic tautomers partially loose aromaticity.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | DOUBLE-PROTON-TRANSFER; DENSITY-FUNCTIONAL THEORY; CONCERTED MECHANISM CONTROVERSY; EXCITED-STATE DYNAMICS; MODEL BASE-PAIRS; 7-AZAINDOLE DIMER; PHOTOINDUCED TAUTOMERIZATION; ENZYMATIC CATALYSIS; FORMAMIDE-WATER; AB-INITIO; |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie > Chair of Chemistry III - Physical Chemistry (Molecular Spectroscopy and Photochemistry) > Prof. Dr. Bernhard Dick |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 14 Dec 2018 13:20 |
| Last Modified: | 27 Feb 2019 07:40 |
| URI: | https://pred.uni-regensburg.de/id/eprint/2157 |
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