1. Structure and vibrational spectroscopy of cyclic diketones and their hydrogen bonded complexes in cold inert gas matrices Amit K. Samanta, Prasenjit Pandey, Anamika Mukhopadhyay and Tapas Chakraborty Department of Physical Chemistry, Indian Association for the Cultivation of Science, Calcutta, India IACS

2. Conformers and tautomers of cyclohexanediones IACS

3. Diketo 4.2 kcal/Mol Trans monoenol (hydrogen bonded) 0.0 Cis monoenol 6.8 kcal/mol Relative energies DFT/6-311++G(d,p) Means of identification: Infrared spectroscopy in cold inert gas matrices 1,2 cyclohexanedione IACS

4. Wavenumber (cm -1 ) 1720 1785 1674 Wavenumber (cm -1 ) 1740 # 600 9001200 1500 1800 2100 2400 2700 3000 3300 3600 Wavenumber (cm -1 ) 1684 1668 FTIR spectrum of 1,2-cyclohexanedione in Ar matrix at 8 K 3463 3540 3686 # B3LYP/6-311++G(d,p) IACS

5. Chair (C) Twist boat (T) Relative energies DFT/6-311++G(d,p) 0.0 0.25 kcal/mol 1,4 cyclohexanedione CC 3.16 kcal/mol CT 3.37kcal/mol TT 3.62 kcal/mol Relative energies DFT/6-311++G(d,p) C–H···O hydrogen bonded dimers IACS

6. 1733 1716 600 9001200 1500 1800 2100 2400 2700 3000 3300 3600 Wavenumber (cm -1 ) 1740 FTIR spectrum of 1,4-cyclohexanedione in N 2 matrix at 8 K 1737 1741 1720 1727 IACS

7. 8K 20K 30K Effects of annealing on spectral features Effects of higher sample concentrations in the gas mixture IACS

8. Diketo Monoenol Chair 0.0 Boat 1.3 kcal/mol Twist boat 4.03 kcal/mol Cis monoenol (1.28 kcal/mol) Trans monoenol (3.2 kcal/mol) Mixed Dimer (O-H---O) Dimers Keto Dimer (C-H---O) 1,3-cyclohexanedione IACS

9. 1721 1741 1724 1749 1716 1717 1742 1739 1719 Wavenumber (cm -1 ) 1200 1500 1800 2100 2400 2700 3000 FTIR spectrum of 1,3-cyclohexanedione in N 2 matrix at 8 K Chair diketo Boat diketo IACS

10. FTIR spectra of 1,3-cyclohexanedione in CCl 4 solution 0.01M 0.02M 0.03M 0.04M IACS

11. Dimer binding # energy Proton affinity # C-H∙∙∙O hydrogen-bonded mixed dimers in room-temperature solutions CBN∙∙∙CHCl 3 CPN∙∙∙CHCl 3 CHN∙∙∙CHCl 3 3.64 kcal/mol3.95 kcal/mol4.39 kcal/mol C=O str. frequency 198 kcal/mol204 kcal/mol 208 kcal/mol 1786 cm -1 1748 cm -1 1716 cm -1 System studied: Chloroform (donor) and small cyclic ketones (acceptor) # DFT/B3LYP/6-311++G(d,P) IACS

12. Blue shifting of chloroform C-H stretching fundamental on complexation # DFT/B3LYP/6-311++G(d,p) CHN  CHCl 3 +1.0 -28.2 CPN  CHCl 3 +2.0 -30.3 CBN  CHCl 3 +5.0 -21.7 Experiment Theory #  C-H  C-H cm -1 cm -1 Complex Green: CBN Red: CPN Blue: CHN Blue shifts occurs with enhancement in transition intensity IACS

13. monomer Ketone:chloroform 1:1 1:5 1:10 1:15 1:20 Anomalous red-shifts of C=O stretching fundamentals 1786 1780 1748 1729 1716 1708 cyclohexanone cyclopentanone cyclobutanone  Red shift of C=O stretching is uncorrelated with blue shifts of C–H stretching  Red shifts of C=O stretching has no correlation with the dimer binding energy IACS

14. Acknowledgement Amit K Samanta Prasenjit Pandey Biman Bandyopadhyay Anamika Mukhopadhyay Moitrayee Mukherjee Financial Support: Department of Science and Technology, Govt. of India Council of Scientific and Industrial Research, Govt. of India IACS