Rotational spectra of propargyl alcohol dimer: O-H O, O-H , C-H interactions

Devendra Mani and E. Arunan Department of Inorganic & Physical Chemistry,

Indian Institute of Science, Bangalore, India.

Pulsed Nozzle Fourier Transform Microwave spectrometer (PNFTMW)

(a) Molecule of Astro-physical interest

– Vinyl alcohol (C2H4O) was found in 2001.

– Propanal (C3H6O) was found in 2006.

– Will propargyl alcohol (C3H4O) be found ?

(b) Combustion

Propargyl radical is considered to be precursor in soot formation.

C3H3 + C3H3 C6H6 or C6H5 +H

Why study propargyl alcohol?

Both groups can act as H-bond donor/acceptor

c) Multifunctional molecule , like phenylacetylene

Offers many possibilities for H-bonding !

Phac-H2ORef1

1. M. Goswami and E. Arunan, Phys. Chem. Chem. Phys., 2011, 13, 14153–141622. M. Goswami and E. Arunan, J. Mol. Spectrosc., 2011 ,268,1-2,147-156

Phac-H2SRef2

Propargyl alcohol (monomer) Due to internal motion of –OH group, this molecule can mainly exist as two conformers: Gauche and trans

100 200 300 400 500 600 700 800 900 1000-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

En

erg

y (

kc

alm

ol-1

)

D(C2C3O1H4)

1 kcalmol-1

Gauche

Cistrans

Relaxed scan at mp2/6-311+(d,p)

Rotational Spectrum • Many groups in 1960s worked on propargyl alcohol1,2.

• Recently in 2005, Pearson et al. revisited the rotational spectrum of this molecule3.

• Only gauche conformer could be observed and no spectroscopic signature for

trans form was present.

• Tunneling frequencies between gauche conformers for OH species and OD species have been determined to be 652.38GHz and 213.48 GHz respectively.

• For propargyl mercaptan (HC≡CCH2SH)4 and propargyl selenol (HC≡CCH2SeH)5 also only gauche conformer was observed!

• Can trans form be observed in molecular beams ?

• Can it be stabilized via complex formation with e.g., Ar/H2O? 1. Eizi Hirota, Journal of Molecular Spectroscopy 26, 335-350 (1968)2. K. Bolton, N.L. Owen, J. Sheridan, Nature 217 (1968) 164.3. J.C. Pearson , B.J. Drouin , Journal of Molecular Spectroscopy 234 (2005) 149–1564. F. Scappini et al. CPL, 1975, 33(3), 499-501. 5. Harald Møllendal et al. J. Phys. Chem. A 2010, 114, 5537–5543

Ar Propargyl alcohol complex

2.8A0

3.8A0

oxygen-hydrogen-Argon angle=145.20

Argon-pi bond-carbon angle = 74.50

COHAr dihedral angle = 25.90

At MP2/6-311+G(3df,2p)

oxygen-hydrogen-Argon angle=138.80

COHAr dihedral angle ~ 00

Ar g-PA Ar t-PA

A/MHz 4312 13563

B/MHz 1684 932

C/MHz 1281 863

μa 0.9 D 1.8 D

μb 1.1 D 1.3 D

μc 0.8 D 0.0 D

Ab-initio calculated rotational constants and dipole-moment components

Constants Lower set Upper set Line centreA/MHz 4346.1695(20) 4346.1785(22) 4346.1735(11)B/MHz 1617.15059(41) 1617.15664(47) 1617.15334(24)C/MHz 1245.42035(28) 1245.42070(32) 1245.42047(18)DJ/kHz 7.3141(43) 7.3166(49) 7.3132(27)

DJK/kHz 61.552(33) 61.569(38) 61.552(21)

DK/kHz -55.30(43) -55.00(48) -55.17(24)

d1/kHz -2.1765(30) -2.1729(34) -2.1738(18)

d2/kHz -0.7138(11) -0.7150(13) -0.71468(73)# transitions 45 45 50

rms deviation /kHz 4.7 5.3 3.1

D. Mani, E. Arunan, ChemPhysChem 14, 754 (2013)

Fitted constants

Ar g-PA

Ar methanol

Ar t-PA

Nature of interactions: AIM analysis

22 unassigned lines which depend only on PA concentration!!

None of these lines corresponds to the monomer spectra!

Can it be due to higher clusters of propargyl alcohol , dimer or may be trimer?

Propargyl alcohol dimer

A/MHz 2286

B/MHz 1234

C/MHz 1209

μa /D 1.8

μb /D 1.5

μc /D 2.1

E/kJ.mol-1 31.8

At MP2/6-311+G(3df, 2p)

View 1 View 2

He used as carrier gas

~6% of which was flown through a bubbler containing propargyl alcohol

Dependence of the signals was checked by turning off the flow through PA sample.

Already observed signals were used as the initial guess and other signals were searched according to the dimer predictions.

Total 51 transitions could be fitted to the experimental uncertainty.

Observed signals for PA-dimer

J K-1 K+1 J K-1 K+1 Frequency

(MHz) Residue(MHz) Type

2 1 2 1 1 1 4525.0904 0.0026 a 2 0 2 1 0 1 4550.2612 0.0003 a 2 1 1 1 1 0 4576.2612 0.0011 a 3 0 3 2 1 1 5601.3099 0.0078 c 2 1 2 1 0 1 5696.4442 -0.0001 b 2 1 1 1 0 1 5773.2026 -0.0013 c 3 1 3 2 1 2 6787.2685 0.0018 a 3 0 3 2 0 2 6824.2441 -0.0010 a 3 2 2 2 2 1 6825.9070 -0.0010 a 3 2 1 2 2 0 6827.5363 -0.0005 a 3 1 2 2 1 1 6864.0172 0.0014 a 4 0 4 3 1 2 7834.1436 -0.0013 c 3 1 3 2 0 2 7933.4491 -0.0011 b 4 0 4 3 1 3 7987.6514 -0.0022 b 5 1 4 4 2 3 8012.6465 -0.0007 b 3 1 2 2 0 2 8086.9612 0.0024 c 2 2 1 1 1 0 8090.3430 0.0014 b 2 2 0 1 1 0 8090.7486 -0.0004 c 2 2 0 1 1 1 8116.3340 -0.0023 b 4 2 3 3 2 2 9100.6989 0.0002 a 4 2 2 3 2 1 9104.7685 0.0032 a 4 3 2 3 3 1 9101.7826 -0.0050 a 4 3 1 3 3 0 9101.8119 0.0008 a 4 1 4 3 1 3 9049.0136 0.0003 a 4 0 4 3 0 3 9096.8586 0.0000 a

4 1 3 3 1 2 9151.3160 -0.0009 a 6 1 6 5 2 3 9810.4390 0.0031 b 5 0 5 4 1 3 10050.4868 0.0000 c 5 0 5 4 1 4 10306.2977 -0.0014 b 3 2 2 2 1 1 10339.9928 0.0033 b 3 2 1 2 1 1 10342.0246 -0.0011 c 4 1 3 3 0 3 10414.0309 0.0003 c 3 2 1 2 1 2 10418.7855 0.0002 b 4 1 4 3 0 3 10158.2185 0.0002 b 5 1 5 4 1 4 11310.1924 0.0000 a 5 0 5 4 0 4 11367.6588 0.0000 a 5 2 4 4 2 3 11375.0490 -0.0019 a 5 4 1 4 4 0 11376.7770 0.0009 a 5 4 2 4 4 1 11376.7770 0.0012 a 5 2 3 4 2 2 11383.1636 0.0007 a 5 3 3 4 3 2 11377.2647 -0.0004 a 5 3 2 4 3 1 11377.3477 0.0006 a 5 1 4 4 1 3 11438.0039 0.0011 a 5 1 5 4 0 4 12371.5539 0.0018 b 4 2 3 3 1 2 12576.6710 -0.0015 b 6 0 6 5 1 5 12632.3367 0.0027 b 4 2 2 3 1 3 12736.2806 -0.0033 b 3 3 1 2 2 0 12746.5296 -0.0011 b 3 3 0 2 2 0 12746.5296 -0.0050 c 3 3 1 2 2 1 12746.9447 0.0066 c 5 1 4 4 0 4 12755.1770 0.0023 c

A /MHz 2321.83350(42)

B /MHz 1150.47741(21)

C /MHz 1124.88979(16)

DJ /kHz 1.8422(31)

DJK /kHz 0.375(11)

DK /kHz -0.982(40)

d1 /kHz -0.0457(27)

d2 /kHz -0.1498(22)

s/kHz 2.5

# transitions 51

Fitted Constants

D. Mani, E. Arunan, manuscript under preparation

H-16 as Deuterium

Isotopic substitution: 1

A /MHz 2299.9

B /MHz 1148.4

C /MHz 1119.6

Calculated constants

J K-1 K+1 J K-1 K+1 Frequency

(MHz)obs -cal(MHz)

2 1 1 1 0 1 5748.995 -0.0007 3 1 3 2 1 2 6749.679 -0.0055 3 0 3 2 0 2 6797.907 -0.0005 3 1 2 2 1 1 6851.091 0.0018 3 1 3 2 0 2 7864.025 0.0043 4 0 4 3 1 3 7994.144 0.0013 4 1 4 3 1 3 8998.544 -0.0008 4 0 4 3 0 3 9060.247 -0.0095 4 2 3 3 2 2 9067.065 0.014 4 2 2 3 2 1 9074.314 0.008 4 1 3 3 1 2 9133.683 -0.0103 4 1 4 3 0 3 10064.66 -0.0021 5 0 5 4 1 4 10315.15 0.0041 5 1 5 4 1 4 11246.55 -0.0021 5 0 5 4 0 4 11319.56 0.004 5 2 4 4 2 3 11332.59 -0.0098 5 2 3 4 2 2 11347.03 -0.0068 5 1 4 4 1 3 11415.34 0.0065 5 1 5 4 0 4 12250.95 0.0038

Observed signals

Fitted constants

A /MHz 2297.8207(52)

B /MHz 1150.4122(13)

C /MHz 1116.6032(14) DJ /kHz 1.826(20) DJK /kHz 0.40(14) DK /kHz -1.000 d1 /kHz -0.059(17) d2 /kHz -0.174(10)

s/kHz 7.9

#transitions 19

D. Mani, E. Arunan, manuscript under preparation

H-8 as Deuterium

A /MHz 2304.9

B /MHz 1146.9

C /MHz 1124.3

Isotopic substitution: 2

Calculated constants

J K-1 K+1 J K-1 K+1 Frequency

(MHz)obs -cal(MHz)

3 1 3 2 1 2 6801.5120 0.0030 3 0 3 2 0 2 6828.0980 -0.0050 3 1 2 2 1 1 6856.1370 0.0006 4 1 4 3 1 3 9068.2370 -0.0006 4 0 4 3 0 3 9102.9418 -0.0001 4 2 3 3 2 2 9104.9295 -0.0009 4 2 2 3 2 1 9107.0125 0.0013 4 1 3 3 1 2 9141.0600 0.0021 4 1 4 3 0 3 10178.2245 0.0000 5 1 5 4 1 4 11334.5930 0.0007 5 0 5 4 0 4 11376.7613 0.0001 5 2 4 4 2 3 11380.5950 -0.0001 5 2 3 4 2 2 11384.7490 -0.0012 5 1 4 4 1 3 11425.5832 -0.0001

Observed signals

A /MHz 2301.8767(51)

B /MHz 1147.29807(87)

C /MHz 1129.08541(85)

DJ /kHz 1.7851(72)

DJK /kHz 0.233(51)

DK /kHz -1.000

d1 /kHz -0.042(10)

d2 /kHz -0.1130(33)

s/kHz 2.5

#transitions 14

Fitted constants

D. Mani, E. Arunan, manuscript under preparation

Isotopic substitution: 3

H-16 and H-8 as Deuterium

A /MHz 2283.2

B /MHz 1144.6

C /MHz 1119.3

Calculated constants

J K-1 K+1 J K-1 K+1 Frequency

(MHz)obs -cal(MHz)

3 1 3 2 1 2 6764.8930 -0.0016 3 0 3 2 0 2 6802.1560 -0.0008 3 2 2 2 2 1 6803.9150 0.0000 3 2 1 2 2 0 6805.6330 -0.0010 3 1 2 2 1 1 6842.3510 -0.0094 2 2 1 1 1 1 7992.9680 0.0025 4 0 4 3 1 3 7994.1390 -0.7342 4 1 4 3 1 3 9019.1860 0.0162 4 0 4 3 0 3 9067.3170 -0.0018 4 2 3 3 2 2 9071.3630 -0.0005 4 2 2 3 2 1 9075.6600 0.0053 4 1 3 3 1 2 9122.4200 -0.0051 5 0 5 4 1 4 10306.3045 0.0074 5 1 5 4 1 4 11272.8660 -0.0012 5 0 5 4 0 4 11330.5803 -0.0135 5 2 3 4 2 2 11346.9195 -0.0024 5 1 4 4 1 3 11401.8630 0.0051

Observed signals

A /MHz 2282.0237(32)

B /MHz 1146.9285(19)

C /MHz 1121.1011(21)

DJ /kHz 1.764(25)

DJK /kHz -0.21(18)

DK /kHz -1.0000

d1 /kHz -0.054(25)

d2 /kHz -0.118(17)

s/kHz 8.7

#transitions 17

Fitted constants

D. Mani, E. Arunan, manuscript under preparation

AIM analysis

O-H O C-H p

O-Hp

Contact ρ(r) in a.u. 2ρ(r) in a.u.

OHO 0.0233 0.0921

OHp 0.0156 0.0501

CHp 0.0058 0.0166

(H2O)2

H2OC2H2(C2H2)2

CH4C2H2H2OC2H4

(CH3OH)2

Contact Complex ρ(r) in a.u. 2ρ(r) in a.u.

OHO

PA-dimer 0.0233 0.0921

Water-dimer 0.0215 0.0960

Methanol-dimer 0.0256 0.1018

OHp

PA-dimer 0.0156 0.0501

Acetylene..water 0.0100 0.0324

Ethylene…water 0.0100 0.0291

CHp

PA-dimer 0.0058 0.0166

methane_acetylene 0.0042 0.0109

acetylene_dimer 0.0064 0.0178

D. Mani, E. Arunan, manuscript under preparation

Other face of methanol: The “carbon bond”.

ESP value at face centre +50.2 kJ.mol-1

Tetrahedral face of methane has a –ve centre!

ESP value at face centre = -7.5 kJ.mol-1

Methanol ESP surface

Microwave spectra of complexes like CH4HF/HCl/HCN and CH4 H2O show that the hydrogen of HX molecule points towards the tetrahedral face of methane.

Microwave spectra of CH4ClF complex shows that the Cl points towards the tetrahedral face of methane.

AIM studies confirm the presence of interactions between carbon of methane and hydrogen of HX molecules as well as Cl of ClF leading to the formation of a hydrogen bond and halogen bond respectively.

What are the bonding properties of the CH3 face of methanol ?

Being electropositive can this face interact with electron rich centres of molecules like water ?

H2OCH3OH complex was optimized taking initial geometry in which oxygen of water points towards the CH3 face of methanol.

3.167 Å

BSSE corrected interaction energy = 4.2 kJ mol-1

Electron density ρ(r), at intermolecular b.c.p. = 0.0050 a.u.

Laplacian of electron density 2ρ(r) at intermolecular b.c.p. = 0.0248 a.u.

H2OCH3OH complex

b.c.p.

Is this a general interaction ?

Optimized geometries for (a) H2O•••CH3OH, (b) H2S•••CH3OH, (c) HF•••CH3OH, (d) HCl•••CH3OH, (e)HBr•••CH3OH, (f) LiF•••CH3OH, (g) LiCl•••CH3OH, (h) LiBr•••CH3OH, (i) ClF•••CH3OH, (j) H3N•••CH3OH, (k) H3P•••CH3OH complexes.

Similar interaction with other molecules

D.Mani, E. Arunan, PCCP, DOI: 10.1039/C3CP51658J

Nomenclature ?

D.Mani, E. Arunan, PCCP, DOI: 10.1039/C3CP51658J

Conclusions

Rotational spectra of PA-dimer and its three deuterated isotopologues has been observed and fitted by a semirigid rotor asymmetric top Hamiltonian.

Observed rotational constants are close to the Ab-initio predicted structure.

AIM calculations show that in the dimer two monomer entities are in a three point contact having O-HO, O-H p , C-H p interactions.

54 lines remain unassigned which could be due to higher PA-clusters.

Acknowledgements My group

Department of Science and Technology, India. Indo-French Centre of Pure and Applied Research. Council of Industrial and Scientific Research, India. Royal Society of Chemistry (PCCP) for travel grant. Indian Institute of Science, Bangalore, India.

Thank you

for your kind attention.