Presentation on theme: "Rotational spectra of propargyl alcohol dimer: O-H O, O-H , C-H interactions Devendra Mani and E. Arunan Department of Inorganic & Physical."— Presentation transcript:
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.
(a) Molecule of Astro-physical interest – Vinyl alcohol (C 2 H 4 O) was found in 2001. – Propanal (C 3 H 6 O) was found in 2006. – Will propargyl alcohol (C 3 H 4 O) be found ? (b) Combustion Propargyl radical is considered to be precursor in soot formation. C 3 H 3 + C 3 H 3 C 6 H 6 or C 6 H 5 +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-H 2 O Ref1 1.M. Goswami and E. Arunan, Phys. Chem. Chem. Phys., 2011, 13, 14153–14162 2.M. Goswami and E. Arunan, J. Mol. Spectrosc., 2011,268,1-2,147-156 Phac-H 2 S Ref2
Propargyl alcohol (monomer) Due to internal motion of –OH group, this molecule can mainly exist as two conformers: Gauche and trans Relaxed scan at mp2/6-311+(d,p)
Rotational Spectrum Many groups in 1960s worked on propargyl alcohol 1,2. Recently in 2005, Pearson et al. revisited the rotational spectrum of this molecule 3. 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≡CCH 2 SH) 4 and propargyl selenol (HC≡CCH 2 SeH) 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/H 2 O? 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) 149–156 4.F. Scappini et al. CPL, 1975, 33(3), 499-501. 5. Harald Møllendal et al. J. Phys. Chem. A 2010, 114, 5537–5543
Ar g-PAAr t-PA A/MHz431213563 B/MHz1684932 C/MHz1281863 μaμa 0.9 D1.8 D μbμb 1.1 D1.3 D μcμc 0.8 D0.0 D Ab-initio calculated rotational constants and dipole-moment components Ab-initio calculated rotational constants and dipole-moment components
ConstantsLower setUpper setLine centre A/MHz4346.1695(20)4346.1785(22)4346.1735(11) B/MHz1617.15059(41)1617.15664(47)1617.15334(24) C/MHz1245.42035(28)1245.42070(32)1245.42047(18) D J /kHz7.3141(43)7.3166(49)7.3132(27) D JK /kHz61.552(33)61.569(38)61.552(21) D K /kHz-55.30(43)-55.00(48)-55.17(24) d 1 /kHz-2.1765(30)-2.1729(34)-2.1738(18) d 2 /kHz-0.7138(11)-0.7150(13)-0.71468(73) # transitions45 50 rms deviation /kHz18.104.22.168 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/MHz2286 B/MHz1234 C/MHz1209 μ a /D1.8 μ b /D1.5 μ c /D2.1 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.
A /MHz 2321.83350(42) B /MHz 1150.47741(21) C /MHz 1124.88979(16) D J /kHz 1.8422(31) D JK /kHz 0.375(11) D K /kHz -0.982(40) d 1 /kHz -0.0457(27) d 2 /kHz -0.1498(22) /kHz 2.5 # transitions51 Fitted Constants D. Mani, E. Arunan, manuscript under preparation
H-16 as Deuterium Isotopic substitution: 1 A /MHz2299.9 B /MHz1148.4 C /MHz1119.6 Calculated constants
Fitted constants A /MHz 2297.8207(52) B /MHz 1150.4122(13) C /MHz 1116.6032(14) D J /kHz 1.826(20) D JK /kHz 0.40(14) D K /kHz d 1 /kHz -0.059(17) d 2 /kHz -0.174(10) /kHz 7.9 #transitions19 D. Mani, E. Arunan, manuscript under preparation
H-8 as Deuterium A /MHz2304.9 B /MHz1146.9 C /MHz1124.3 Isotopic substitution: 2 Calculated constants
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 CH 4 HF/HCl/HCN and CH 4 H 2 O show that the hydrogen of HX molecule points towards the tetrahedral face of methane. Microwave spectra of CH 4 ClF 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 CH 3 face of methanol ? Being electropositive can this face interact with electron rich centres of molecules like water ?
H 2 O CH 3 OH complex was optimized taking initial geometry in which oxygen of water points towards the CH 3 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 2 ρ(r) at intermolecular b.c.p. = 0.0248 a.u. H 2 O CH 3 OH complex b.c.p. Is this a general interaction ?
Optimized geometries for (a) H 2 OCH 3 OH, (b) H 2 SCH 3 OH, (c) HFCH 3 OH, (d) HClCH 3 OH, (e)HBrCH 3 OH, (f) LiFCH 3 OH, (g) LiClCH 3 OH, (h) LiBrCH 3 OH, (i) ClFCH 3 OH, (j) H 3 NCH 3 OH, (k) H 3 PCH 3 OH 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-H O, O-H , C-H 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.