64 th OSU International Symposium on Molecular Spectroscopy

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64 th OSU International Symposium on Molecular Spectroscopy Infrared spectroscopic demonstration of cooperative strengthening

64 th OSU International Symposium on Molecular Spectroscopy Infrared spectroscopic demonstration of cooperative strengthening of an intramolecular O–H O hydrogen bond by a weak C–H O counterpart Amit K Samanta, Prasenjit Pandey, Biman Bandyopadhyay and Tapas Chakraborty H–C 1, 2 -cyclohexanedione IACS - Tautomer Department of Physical Chemistry, Indian Association for the Cultivation of Science, Kolkata, India

Cooperative effects in H-bonded cyclic clusters of water Cooperativity in hydrogen bonding: It is

Cooperative effects in H-bonded cyclic clusters of water Cooperativity in hydrogen bonding: It is an important attribute of interconnected hydrogen bonds. The effect refers to enhanced stabilization of a system with more than one interconnected HBs compared to the sum of the energies of the equivalent but isolated H-bonded pairs. Classic examples are small cyclic clusters of water. H O H H Binding energy [B 3 LYP/6 -311++(d, p)] H-bonded OH Dimer 14. 7 k. J/mol 3700 cm-1 Trimer (cyclic) 16. 1 k. J/mol 3499 cm-1 Tetramer (cyclic) 23. 1 k. J/mol 3388 cm-1 Pentamer (cyclic) 25. 1 k. J/mol 3349 cm-1 Hexamer (cyclic) 26. 2 k. J/mol 3327 cm-1 IACS Ohno et al. PCCP, 7 (2005) 3005

Cooperativity and conformational preference by CH O bonding common acceptor of 2 HBs 3

Cooperativity and conformational preference by CH O bonding common acceptor of 2 HBs 3 -methylcyclohexane-1, 2 -dione Interconnected hydrogen bonds H O H IACS H H

Cooperativity and conformational preference through CH O Predictions of DFT/B 3 LYP/6 -311++G(d, p)

Cooperativity and conformational preference through CH O Predictions of DFT/B 3 LYP/6 -311++G(d, p) theory H-bonding 2. 043 Å 2. 4 50 (Me. CD) 0 88 . 0 96 1. 1 0 09 1. 6 -4. 18 group with hydrogen bond distance 0 1. 09 kcal/mol Evolution of electronic structure parameters of C–H and C=O 2. 620 2. 055 1. 093 -7. 79 0 Changes inkcal/mol intensities of those transitions (CD) Energy in kcal/mol 2. 070 -4. 59 IACS -4. 59

4 K closed cycle cryogenic system To Vacuum Pump Out In } Coolant Gas

4 K closed cycle cryogenic system To Vacuum Pump Out In } Coolant Gas Temperature Sensor KBr Window Matrix gas expansion Needle IACS

Scheme of measurements Mid-IR spectrosocopy IACS

Scheme of measurements Mid-IR spectrosocopy IACS

s 3466 3460 IR spectra of matrix isolated CD and Me. CD a νOH

s 3466 3460 IR spectra of matrix isolated CD and Me. CD a νOH s (Me. CD) a h (3006) (3034) IACS e h Me. CD CD of the hydrogen. Stability bonded complexes (CD) e

Effect of intramolecular CH O H-bonding on C=O transitions Measured Spectra 1659, 1685 1666

Effect of intramolecular CH O H-bonding on C=O transitions Measured Spectra 1659, 1685 1666 Wavenumber (cm-1) Calculated Spectra IACS 1683

Energetic and geometric correlation between the CH O and OH O H- bonds Dependence

Energetic and geometric correlation between the CH O and OH O H- bonds Dependence 0. 8 of stability on the ring size of three cyclic ketones 2. 060 Energy (kcal/mol) 7 Spectral shifts of C-H and C=O on complex formation 0. 6 a 6 10 Changes in intensities of those transitions 0. 4 2. 055 2. 050 Evolution of electronic structure parameters of C–H and C=O 2. 045 group with 0. 2 hydrogen bond distance 2. 040 0. 0 0 20 40 60 80 100 120 C 7 -C 6 -C 10 -Ha dihedral angle (Degree) IACS 140 O–H O HB length (Å) Stability of the hydrogen-bonded complexes

NBO analysis of some electronic structure parameters B 3 LYP/6 -311++G** 7 19 18

NBO analysis of some electronic structure parameters B 3 LYP/6 -311++G** 7 19 18 Hybridization C 9 -H 17 C 9 -H 18 C 9 -H 19 sp 3. 38 sp 3. 07 C 9 -H 18 C 9 -H 19 sp 3. 26 sp 3. 15 C 9 -H 17 C 9 -H 18 C 9 -H 19 sp 3. 36 sp 3. 21 Occupancy [ * (C–H)] C 9 -H 17 C 9 -H 18 C 9 -H 19 0. 009 0. 005 C 9 -H 17 C 9 -H 18 C 9 -H 19 0. 005 0. 007 0. 005 C 9 -H 17 C 9 -H 18 C 9 -H 19 0. 011 0. 004 Natural Charges O 7 H 19 IACS -0. 691 +0. 231 +0. 211 O 7 H 19 -0. 680 +0. 200 +0. 221 O 7 H 19 -0. 670 +0. 209 +0. 211

Cooperative effect in a H-bonded complex between CD and CHCl 3 84 2. 1

Cooperative effect in a H-bonded complex between CD and CHCl 3 84 2. 1 Å 2. 066 Å 2. 070 Å 2. 066 Å 2. 061Å 2. 27 8Å Bifurcated Interconnected -3. 166 -3. 776 BSSE corrected binding energy (kcal/mol) at MP 2/6 -311++G(d, p) level IACS

Cooperative effect in a H-bonded complex between CD and CHCl 3 Stability of the

Cooperative effect in a H-bonded complex between CD and CHCl 3 Stability of the hydrogen-bonded complexes Spectral shift of C=O transitions for complexation with CHCl 3 1684 1666 1683 Spectral shifts of C-H and C=O on complex formation Wavenumber (cm-1) IACS

Effect of intramolecular CH O H-bonding on C=O transitions 1684 1682. 5 Measured spectra

Effect of intramolecular CH O H-bonding on C=O transitions 1684 1682. 5 Measured spectra Annealing at 20 K Annealing at 30 K 1655 1659 1665 1667 1676 1673 Wavenumber (cm-1) Simulated spectra CHD-CHCl 3 complex 1 CHD-CHCl 3 complex 2 CHD-(CHCl 3)2 complex IACS

Effect of intermolecular CH O bonding on C=O transitions 1673 1678 CD in CCl

Effect of intermolecular CH O bonding on C=O transitions 1673 1678 CD in CCl 4 + CHCl 3 Wavenumber (cm-1) 3453 IACS 3471

Summary We have demonstrated that the intramolecular O–H ···O hydrogen bond in the enol

Summary We have demonstrated that the intramolecular O–H ···O hydrogen bond in the enol tautomer of 1, 2 -cyclohexanedione is stabilized cooperatively by an interconnected weak C–H···O hydrogen bond. The C–H···O hydrogen bond of both intra- and intermolecular types are considered. The effect is predicted by electronic structure calculations by ab initio as well as DFT theoretical methods. The predicted vibrational spectral effects on the systems studied are found to be consistent with the infrared spectra measured in cold inert gas matrices and liquids. IACS

Acknowledgement Co-workers: 1. 2. 3. 4. 5. Amit K Samanta Prasenjit Pandey Biman Bandyopadhyay

Acknowledgement Co-workers: 1. 2. 3. 4. 5. Amit K Samanta Prasenjit Pandey Biman Bandyopadhyay Moitrayee Mukherjee Anamika Mukhopadhyay Financial Support: Department of Science and Technology, Government of India IACS

Group members IACS

Group members IACS