THE MICROWAVE STUDIES OF GUAIACOL (2-METHOXYPHENOL), ITS ISOTOPOLOGUES &

VAN DER WAALS COMPLEXES

Ranil M. Gurusinghe, Ashley Fox and Michael J. Tubergen, Department of Chemistry, Kent State University,

Kent, Ohio 44242.

Motivation

• Intramolecular hydrogen bonding & conformational preferences

• Conformational changes upon forming van-der-Waals complexes : Ar complex Water complex

GUAIACOL (2-METHOXYPHENOL)

Background

Monomer 2-aminoethanol-Ar2-aminoethanol-water

Background

Monomer Glycidol-Water

Guaiacol: Previous Ab initio Studies

C. Agache and V. I. Popa, Monatsh. Chem. 137 (2006) 55-68

Previous Ab initio Studies

global minimum 17.57- 20.92 kJ mol-1 22.17 - 23.43 kJ mol-1

planar planar Non-planarIntramolecular H bond 18.09 – 18.51 kJ mol-1

- -

O. V. Dorofeeva, et al., J. Mol. Struct. 933 (2009) 132-141

Ab initio StudiesMP2/6-311++G(d,p)

anti-syn anti-anti gauche-antiA / MHz 2594.5631 2558.1368 2823.4472B / MHz 1560.7322 1566.9383 1502.1355C / MHz 981.4123 977.8028 1037.4823µ a / D -1.9577 0.7493 -1.1651

µb / D -2.3106 -1.1819 1.3121

µc / D 0.2356 0.0022 1.4967Relative Energy/kJ mol-1 0.00 11.64 16.62

Kent State FTMW Spectrometer

• Range : 10500- 22000 MHz• Resolution : 2.4 kHz

• Carrier Gas : He(30%)/Ne Ar

• Temperature : 25 – 60 0C• Backing pressure : 1.5 atm

• Hydroxyl deuterated guaiacol prepared by stirring of guaiacol with D2O in 1:1 ratio for 48 hrs

Guaiacol SpectrumExperimental Results

A/MHz 2607.0664(6) ΔK/kHz 0.00019(3)

B/MHz 1560.7967(2) δJ/kHz 0.000021(1)

C/MHz 982.8721(1) δK/kHz 0.00011(1)

ΔJ/kHz 0.000056(2) N 52

ΔJK/kHz 0.000064(13) Δνrms 0.0025

7 0 7 6 1 67 1 7 6 1 6

7 0 7 6 0 6

7 1 7 6 0 6

Ab initio Results

A / MHz 2594.5631

B / MHz 1560.7322

C / MHz 981.4123

Spectroscopic Constants

Normal 13C(2) 13C(3) 13C(5) 13C(7) 13C( 8) 13C(9) 13C(14) 2H(12)

A/MHz 2607.0664(6) 2602.9051(5) 2571.7285(6) 2580.0272(4) 2606.9526(6) 2594.9216(7) 2600.0172(4) 2598.9887(9) 2546.0430(11)

B/MHz 1560.7967(2) 1536.0989(3) 1551.2280(2) 1560.8336(4) 1559.8295(4) 1559.9680(4) 1545.4638(2) 1525.2094(4) 1555.5731(5)

C/MHz 982.8721(1) 972.4404(1) 974.0418(2) 979.0202(2) 952.4749(1) 980.8136(1) 975.7804(1) 967.5229(2) 972.0485(2)

ΔJ/kHz 0.000056(2) 0.000053(5) 0.000052(2) 0.000059(8) 0.000032(7) 0.000043(7) 0.000048(4) 0.000058(7) 0.000089(8)

ΔJK/kHz 0.000064(13) 0.000057(28) 0.000058(14) 0.000063(36) 0.00018(3) 0.00014(3) 0.000071(19) 0.000010(37) 0.000046(41)

ΔK/kHz 0.00019(3) 0.00027(7) 0.00015(5) 0.00024(80) 0.00022(8) 0.00020(9) 0.00018(5) 0.00019(7) 0.00024(10)

δJ/kHz 0.000021(1) 0.000019(2) 0.000017(1) 0.000021(4) 0.000009(3) 0.000014(3) 0.000016(2) 0.000022(3) 0.000038(4)

δK/kHz 0.00011(1) 0.00011(3) 0.00008(13) 0.00015(6) 0.00008(3) 0.00009(3) 0.00009(2) 0.00017(4) 0.000244(39)

N 52 24 28 25 23 27 26 24 24

Δνrms 0.0025 0.0011 0.0012 0.0014 0.0012 0.0015 0.0009 0.0014 0.0014

C8C9

C2C3

C5

C7

O11

H12

O13

H6

H4

H1

H10C14

H16

H15

H17

Principal-Axis-System Coordinates of 13C and 2H from: Kraitchman Analysis & Ab-initio Method

IsotopomerKraitchman Ab-initio

| a| / Å | b| / Å | c| / Å a / Å b / Å c / Å

13C(2) 2.2843 0.5690 0.0082 2.2967 -0.5969 0.029013C(3) 1.4021 1.6485 0.0147 i 1.3851 -1.6541 -0.014013C(5) 0.0904 i 1.4285 0.0249 0.0045 -1.3970 -0.018013C(7) 0.4484 0.0885 0.0261 -0.4478 -0.0757 -0.045413C(8) 0.4142 0.9553 0.0075 0.4724 0.9913 0.010913C(9) 1.7929 0.7352 0.0226 1.8401 0.7280 0.0083

13C(14) 2.7487 0.8002 0.0119 -2.7409 -0.6903 0.06421H(12) 1.0230 2.1655 0.0644 -0.9372 2.2381 0.0314

C8C9

C2C3

C5

C7

O11

H12

O13

H6

H4

H1

H10C14

H16

H15

H17

Guaiacol-Ar: Ab Initio StudiesMP2/6-311++G(d,p)

Structure

Dipole Moments / D Rotational Constants / MHzRelative E/

kJ mol-1µa µb µc A B C

1 -1.2974 -1.8323 2.0114 1065.9583 874.4618 751.2829 0.00

2 1.8671 0.5410 2.2914 989.6771 927.2382 750.2371 0.75

3 -0.3123 3.0154 0.2285 2097.6937 526.6349 422.3077 3.33

1 2 3

Guaiacol-Ar SpectrumExperimental Results

A/MHz 1142.6041(14) ΔK/kHz 0.01482(3)

B/MHz 801.1291(7) δJ/kHz 0.000669(1)

C/MHz 705.8670(1) δK/kHz -0.002499(12)

ΔJ/kHz 0.002594(3) N 43

ΔJK/kHz

-0.007886(24) Δνrms 0.0034

8 0 8 7 1 7

8 1 8 7 1 7 8 0 8 7 0 7 8 1 8 7 0 7

Ab initio ResultsA / MHz 1065.9583B / MHz 874.4618C / MHz 751.2829

Principal-Axis-System Coordinates of Ar atom from: Kraitchman Analysis & Ab Initio Method

• More Ab-initio modeling need to be done for Guaiacol-Ar complex

Kraitchman Ab –Initio

| a| / Å | b| / Å | c| / Å a / Å b / Å c / Å

2.3657 1.1360 0.5282 - 1.634308 2.035544 0.509286

Guaiacol-Water ComplexAb Initio Studies: MP2/6-311++G(d,p)

Structure

Dipole Moments / D Rotational Constants / MHzRelative

E/ kJ mol-1

µa µb µc A B C

1 0.0859 1.9007 -1.2610 2017.7828 973.4661 784.3017 0.00

2 -0.2980 -1.2651 -0.1123 1490.8885 1091.8987 944.1165 4.57

2 4.0033 -1.3853 -0.6927 1720.5131 895.8985 596.4990 6.25

4 -3.1880 -0.3006 0.5456 2061.0862 908.5115 650.8791 16.43

1 2 3 4

Summary

• Ab initio calculations & rotational spectra for guaiacol, its isotopologues, Ar & water complexes

• Lowest energy conformation of guaiacol accommodates intramolecular hydrogen bonding

• Guaiacol-Ar : More modeling need to be done

• Guaiacol-Water : Work in progress

Acknowledgements

• Ohio Super Computer Center

• Kent State University, Kent, Ohio

Principal-Axis-System Coordinates of 13C and 2H from: Kraitchman Analysis & Ab-initio Method

Isotopomer

Kraitchman Ab-initio| a| / Å | b| / Å | c| / Å a / Å b / Å c / Å

13C(2) 2.2843(6) 0.5690(26) 0.0082(1828) 2.2967 -0.5969 0.029013C(3) 1.4021(11) 1.6485(9) 0.0147 I(-1020 i) 1.3851 -1.6541 -0.014013C(5) 0.0904 I(-165i) 1.4285(10) 0.0249(601) 0.0045 -1.3970 -0.018013C(7) 0.4484(33) 0.0885(169) 0.0261(573) -0.4478 -0.0757 -0.045413C(8) 0.4142(36) 0.9553(15) 0.0075(1998) 0.4724 0.9913 0.010913C(9) 1.7929(8) 0.7352(20) 0.0226(663) 1.8401 0.7280 0.0083

13C(14) 2.7487(5) 0.8002(18) 0.0119(1255) -2.7409 -0.6903 0.06421H(12) 1.0230(14) 2.1655(6) 0.0644(232) -0.9372 2.2381 0.0314

C8C9

C2C3

C5

C7

O11

H12

O13

H6

H4

H1

H10C14

H16

H15

H17

Guaiacol-Ar models: Structures 1 & 2

3.549 Å, 3.22 Å 3.349 Å, 3.481 Å

1 2

Hydroxyl deuterated Guaiacol Preparation

• Rapid stirring of guaiacol with D2O in 1:1 ratio for 48 hrs

• Filtered out the organic layer• Dried in a desiccator for another 48 hours• Confirmed with NMR spectroscopy

O

D

O

CH3