Infrared spectroscopy probing of blue-shifting C–HO hydrogen-bonded complexes between cyclic ketones and haloforms

Anamika Mukhopadhyay, Amit K. Samanta, Biman Bandyopadhyay, Prasenjit Pandey and Tapas Chakraborty

Physical Chemistry DepartmentIndian Association for the Cultivation of Science

Jadavpur, Calcutta-700032, India

IACS

65th OSU Symposium on Molecular SpectroscopyDate: 24th June

RI17

2. Blue shifting hydrogen bonds (Bond energy < 4 kcal/mol )

1. Classical hydrogen bonds (Bond energy 5-10 kcal/mol )

Spectral manifestation of blue-shifting hydrogen bonds

Dimethylether-fluoroform

Methanol dimer

1386 1395 1404

Wavenumber (cm-1)1386 1395 1404

Wavenumber (cm-1)

Wavenumber (cm-1)3036 3054

Intensity lowering

C–H

1386 1395 1404

Wavenumber (cm-1)1386 1395 1404

Wavenumber (cm-1)

Wavenumber (cm-1)

Intensity Enhancement

3515 3643

O–H

O

O

O

O H

Weak H-bonded complexesWeak H-bonded complexes of our interest

OH–C Cl3

H–C Cl3O

H–C Cl3O

H–C Cl3O

OH–C X3

OH–C X3

X=F/Cl

H

–C C

l3

H–C Cl3

Cyclopentanone CyclohexanoneCyclobutanone

Cr

Cc

Cc

Cr

Cc

Cc

Cr

Cr

Cr

C=O Strch.frequency cm-1

1788 1748 1716

Proton affinity(kcal/mol)*

198 204 208

Dipole moment (Debye)*

3.68 3.83 3.93

Cc–Cr–Cc (deg) *92.59 108.43 115.28

Hybridyzationof C=O bond*

sp1.99 sp2.09 sp2.19

q(O) * -0.535 -0.561

Selected molecular parameters of the cyclic ketones: MP2/6-31+G*

-0.566

Experimental techniques

2. Solution phase FTIR study

Typical sample concentration in CCl4 solutions is 0.025M

Instrument resolution ~0.5cm-1

1. IR matrix isolation study

KBr Window

Needle

Temperature sensor

IR Beam of an FTIR spectrometer

Temperature ~ 7K

1690 1700 1710 1720 1730 1740

1695 1710 1725 1740

1717 cm-1

1709 cm-1

Ketone : chloroform

1:1

1:5

1:10

1:15

monomer

Changes of νCO band of cyclohexanone in FTIR spectrum in CCl4 on increase of CHCl3 concentration in the solution. A new band develops with a red shift of 8 cm-1 due to complex formation

Effect of C–HO H-bonding on C=O of cyclic ketones

Wavenumber (cm-1)

H–C Cl3O

H–C Cl3O

H–C Cl3O

C=O

8

19

6

(cm-1)

monomer

1:1 complex

E(kcal/mol)

3.64

3.95

4.39

3000 3010 3020 3030 3040 3050

3018cm-1

1cm-1

2cm-1

5cm-1

Wavenumber (cm-1)

C–HO H-bonding results blue-shifting of the chloroform C-H transition

Cl3C–H

Cl3C–H O=

Cl3C–H O=

Cl3C–HO=

Cl3C–HO=<

Mukhopadhyay et al. JPCA 113, 3078, 2009

+5

-2

+14

C-HMP2/6-31+g(d)

Predicted structure of CHCl3 complex with cyclic ketones

MP2/6-31+G(d)

Cl3C–

HO=

Variation of C–H bond length and C-H frequency with intermolecular separation

* Delanoye et al. JACS, 2002, 124, 7490

* Delanoye et al. JACS, 2002, 124, 11854

Theoretical prediction of C-H spectral shifts of the four ether-haloform complexes

∆

C–H

(cm

-1)

(degree)

110 120 130 140 150 160 170 1800

-1

-2

-3

-4

-5

30

35

40

45

50

55

Ene

rgy

(kca

l/m

ol)

Correlation of C-H , binding and hyperconjugation energies with (C3HO)

Mukhopadhyay et al. JPCA 114, 5206, 2010

Bifurcated Interconnected

2.156 Å

2.070 Å 2.042Å2.111Å

2.070 Å 2.081Å

Energy (kcal/mol) B3LYP/6-311++G(d,p)

E -4.7 -3.8

Binding preference through C-H∙∙∙O HB

q(O)

Keto oxygen Enolic oxygen-0.585 -0.682

1660 1680 1700

1,2CHD in CCl4 +CHCl3

1673

νC=O shifts of 1,2CHD on complexation with CHCl3

Wavenumber (cm-1)

1678Solution phase study

1660 1670 1680 1690

1684

1677

16671662

1,2 CHD

1,2 CHD + CHCL3

Wavenumber (cm-1)

In Ar matrix

1,2CHD in CCl4

Solution phase study

νO-H shifts of 1,2CHD on complexation with CHCl3

3453

3471

1,2CHD in CCl4

1,2CHD in CCl4 +CHCl3

BifurcatedInterconnected

Bifurcated Interconnected

n(O)-*(C–H) 4.76 3.69

kcal/mol

3420 3450 3480 3510

Inte

nsit

y

Wavenumber (cm-1)

1,2-CHD-Chloroform (23K annealed) 1,2-CHD

In Ar matrix

Complex peakmonomer peak

Summary :

Blue-shifting C–H∙∙∙O H-bonded complexes between chloroform and cyclic ketones studied here are stable in CCl4 solution at room temperature.

The H-bond acceptor ability of the carbonyl group in cyclic ketones are altered systematically with ring size, and this exerts a systematic effect on blue shifting of the C-H frequency of chloroform .

Geometry of a H-bonded complex is the key determining factor of spectral shifts of the donor acceptor groups.

In the case of chloroform complex with the tautomeric form of 1,2-cyclohexanedione, bifurcated geometry has been identified to be preferred over the interconnected geometry.

Thank You