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

Conformers and tautomers of cyclohexanedionesIACS

Diketo

4.2 kcal/Mol

Trans monoenol (hydrogen bonded)

0.0

Cis monoenol

6.8 kcal/mol Relative energiesDFT/6-311++G(d,p)

Means of identification: Infrared spectroscopy in cold inert gas matrices

1,2 cyclohexanedione

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1000 1200 1400 1600 1800

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1785

1674

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. .( )C O C C O P O H

. .( )C O C C I P O H

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1740 #

600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600Wavenumber (cm-1)

1684

1668

FTIR spectrum of 1,2-cyclohexanedione in Ar matrix at 8 K

3600 3800

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Title

X Axis Title

Infrared (Intensity)

3463

3540

3686

# B3LYP/6-311++G(d,p)

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Chair (C) Twist boat (T)

Relative energiesDFT/6-311++G(d,p)

0 .00.25 kcal/mol

1,4 cyclohexanedione

CC 3.16 kcal/mol

CT 3.37kcal/mol

TT3.62 kcal/mol

Relative energiesDFT/6-311++G(d,p)

C–H···O hydrogen bonded dimers

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1733

1716

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Wavenumber (cm-1)

1710 1720 1730 1740 1750 1760

1726

1733

1716

1740

Wavenumber (cm-1)

1740

FTIR spectrum of 1,4-cyclohexanedione in N2 matrix at 8 K

-500 0 500 1000 1500 2000 2500 3000 3500 4000-50

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1737

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1741

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1720

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1727

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1710 1720 1730 1740 1750

Wavenumber (cm-1)

8K

20K

30K

Effects of annealing on spectral features

1700 1710 1720 1730 1740 1750 1760

Wavenumber (cm-1)

Effects of higher sample concentrations in the gas mixture

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Diketo Monoenol

Chair0.0

Boat1.3 kcal/mol

Twist boat4.03 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

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1680 1750

Wavenumber (cm-1)

1721

17411724

1749

1716

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1719

Wavenumber (cm-1)

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FTIR spectrum of 1,3-cyclohexanedione in N2 matrix at 8 K

Chair diketo

Boat diketo

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Wavenumber (cm-1)

FTIR spectra of 1,3-cyclohexanedione in CCl4 solution

0.01M

0.02M

0.03M

0.04M

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Dimer binding #

energy

Proton affinity #

C-H∙∙∙O hydrogen-bonded mixed dimers in room-temperature solutions

CBN∙∙∙CHCl3 CPN∙∙∙CHCl3 CHN∙∙∙CHCl3

3.64 kcal/mol 3.95 kcal/mol 4.39 kcal/mol

C=O str. frequency

198 kcal/mol 204 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)

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3000 3010 3020 3030 3040 3050

Abs

orba

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(a.u

.)

Wavenumber (cm-1)

Blue shifting of chloroform C-H stretching fundamental on complexation

# DFT/B3LYP/6-311++G(d,p)

CHNCHCl3 +1.0 -28.2

CPNCHCl3 +2.0 -30.3

CBNCHCl3 +5.0 -21.7

Experiment Theory #

C-H C-H cm-1 cm-1 Complex

Green: CBNRed: CPNBlue: CHN

Blue shifts occurs with enhancement in transition intensity

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monomer

Ketone:chloroform 1:1

1:5 1:10 1:15

1:20

Anomalous red-shifts of C=O stretching fundamentals

1770 1800

1786

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1748

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1729

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Wavenumber (cm-1)

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

1700 1720 1740 1760 1780 1800

Wavenumber (cm-1)

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Acknowledgement

Amit K SamantaPrasenjit PandeyBiman Bandyopadhyay

Anamika MukhopadhyayMoitrayee Mukherjee

Financial Support: Department of Science and Technology, Govt. of India Council of Scientific and Industrial Research, Govt. of India

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