1. THE MICROWAVE SPECTRUM AND UNEXPECTED STRUCTURE OF THE BIMOLECULAR COMPLEX FORMED BETWEEN ACETYLENE AND (Z)-1-CHLORO-2-FLUOROETHYLENE
Nazir D. Khan, Helen O. Leung & Mark D. Marshall
Department of Chemistry
Amherst College
Supported by the National Science Foundation

2. Leung, Marshall, Amberger,
Fluoroethylene---HF Complexes
18.7(15)o
21.65o
29.99o
2.734 Å
1.892(14) Å
(14) Å
(68) Å
2.7825(3) Å
(44) Å
Cole & Legon, CPL 400, 419 (2004)
Leung, Marshall, Amberger,
JCP 131, (2009)
Leung & Marshall et. al,
JCP 131, (2009)
2.7522(40) Å
An increase in the number of F substituents has significant effects on the nature of intermolecular interactions.
41.6(51)o
2.020(41) Å
Leung & Marshall, JCP 126, (2007)

3. 1, 1-Difluoroethylene---HX Complexes
3.0762(3) Å
2.3309(4) Å
122.41o
34.22o
Kisiel, Fowler, Legon, J. Chem. Soc.,
Faraday Trans. 88, 3385 (1992)
1.9883(4) Å
2.7825(3) Å
29.99o
Leung, Marshall, Drake, Pudlik, Savji, McCune,
J. Chem. Phys. 131, (2009)
2.65(1) Å
3.01(2) Å
122.4(8)o
53.3(2)o
Leung, Marshall, J. Chem. Phys.
125, (2006) H C C F H H Cl H

4. A Different Structure for the 1, 1, 2-Trifluoroethylene---HF Complex
(14) Å
(68) Å
21.65o
Leung, Marshall, Amberger,
JCP 131, (2009)
41.6(51)o
2.7522(40) Å
2.020(41) Å
Leung & Marshall, JCP 126, (2007)
122.41o
109.0o
“Top binding”
“Side binding”
Top binding is sterically more favorable, and side binding is electrostatically more favorable.

5. 1,1,2-Trifluoroethylene---HX Complexes
2.8694(9) Å
104.5(2)o
2.75(2) Å
69.2(7)o H C
2.02(4) Å
2.752(4) Å
109(1)o
42(5)o C F H H
Leung, Marshall, J. Chem. Phys. 126, (2007)
Leung, Marshall, Cashion, Chen,
J. Chem. Phys. 128, (2008)
2.3416(7) Å
3.0796(5) Å
109.72(4)o
47.73(1)o Cl H
Leung, Marshall, Ray, Kang,
J. Phys. Chem. 114, (2010)

6. Effects of Chlorine Substitution: Chlorofluoroethylenes and chloroethylenes
What is the effect of substituting chlorine atoms for fluorine atoms in various fluoroethylenes?
Chlorine is less electronegative than fluorine
Chlorine is more polarizable
Acids were expected to preferentially bind to fluorine in chlorofluoroethylenes
The primary interaction was expected to be weakened less by additional chlorine substitution than additional fluorine substitution

7. Chlorofluoroethylene---HF Complexes
1.9482(10) Å
(70)o
2.7386(19) Å
29.14o
24.93(1)o F F H H
2.4535(2) Å
1.9445(2) Å
HF preferentially binds to fluorine over chlorine in chlorofluoroethylenes o F F H H H H Cl Cl
2.7574(12) Å
Leung, Marshall, Bozzi, Cohen, Lam,
J. Mol. Spectrosc. 267, 43 (2010) F F
Leung, Marshall, Lee,
In preparation H
41.5(24)o
109.20(61)o F
2.020(18) Å H Cl
Leung, Marshall, Bozzi,
In preparation

8. Vinyl Chloride---HX Complexes
2.319(6) Å
2.59(1) Å
19.8(3)o
102.4(2)o
3.02(1) Å
88.6(2)o
58.5(6)o
2.93(1) Å F H Cl Cl H Cl C H C
2.409 Å
3.386 Å H
Leung, Marshall, J. Phys. Chem. 118, 9783 (2014)
Leung, Marshall, Bozzi, Cohen, Lam,
J. Phys. Chem. 117, 13419 (2013) Cl
Acid identity determines the structure of the
vinyl chloride---HX complex
Minimum energy structure predicted by ab initio calculations for the vinyl chloride---HCl dimer

9. (Z)-1-Chloro-2-fluoroethylene---HCCH Complex
How does HCCH bind to (Z)-1-chloro-2-fluoroethylene?
How do the geometric parameters compare to previous results? ?

10. Ab Initio CalculationsÅ Å
61.44o
104.33o
Fluorine bound minimum Å Å
61.74o
85.67o
Chlorine bound minimum
θZE r
θHCCH
A = MHz B = MHz C = MHz
75 cm-1
A = MHz B = MHz C = MHz
0 cm-1

11. Chirped-Pulse FTMW Spectroscopy
Studied in the GHz region
1% CHFCHCl, 1% HCCH in Ar at ~2 atm backing pressure
Two isotopologues
CHFCH35Cl---HCCH
CHFCH37Cl---HCCH
Nozzle is mounted perpendicular to microwave horns
CHFCH35Cl---HCCH
Ar---CHFCH35Cl *
CHFCH37Cl

12. Balle-Flygare FTMW Spectroscopy
Studied in the GHz region
1% CHFCHCl, 1% HCCH in Ar at ~2 atm backing pressure
Six isotopologues
CHFCH35Cl---HCCH, CHFCH37Cl---HCCH, CHFCH35Cl---H13C13CH, CHFCH37Cl---H13C13CH, CHFCH35Cl---H13CCH, 13CHFCH35Cl---HCCH
Nozzle is mounted parallel to mirror axis, leading to Doppler doubling in each transition.

13. Representative Transition
CHFCH35Cl---HCCH
F’ = 4.5
F” = 3.5
F’ = 1.5
F” = 1.5

14. (Z)-1-chloro-2-fluoroethylene---HCCH Transitions
CHFCH35Cl---HCCH
CHFCH37Cl---HCCH
CHFCH35Cl---H13C13CH
CHFCH37Cl---H13C13CH
13CHFCH35Cl---HCCH
CHFCH35Cl---H13CCH
Total # of transitions
101
104 88 76 6 7
# of a-type transitions 43 50 42 36 2 3
# of b-type transitions 58 54 46 40 4
Hyperfine components
587
533
476
372 16 21
J range
0-10
2-5
Ka range
0-4
0-3
0-1

15. Spectroscopic Constants (MHz)
CHFCH35Cl---HCCH A
(85) B
(35) C
(32)
ΔJ / 10-3
(23)
ΔK / 10-3
(82)
ΔJK / 10-3
(19)
δJ / 10-3
(11)
δK / 10-3
5.2715(12)
χaa
(66)
χbb
(83)
χcc
(79)
RMS
0.0018
Fluorine bound minimum
A = MHz B = MHz C = MHz
Chlorine bound minimum
A = MHz B = MHz C = MHz

16. Spectroscopic Constants (MHz)
CHFCH37Cl---HCCH
CHFCH35Cl---H13C13CH
CHFCH37Cl---H13C13CH
13CHFCH35Cl---HCCH
CHFCH35Cl---H13CCH A
(66)
(90)
(10)
(22)
(18) B
(24)
(33)
(52)
(25)
(23) C
(19)
(28)
(51)
(52)
(48)
ΔJ / 10-3
(14)
(20)
(31)
1.1435(81)
1.1037(75)
ΔK / 10-3
(74)
(10)
(12) *
ΔJK / 10-3
(11)
(19)
(36) *
δJ / 10-3
(63)
(10)
(14) *
δK / 10-3
5.1913(60)
4.987(11)
4.920(21)
5.2715*
χaa
(60)
(72)
(96)
39.819(20)
39.843(16)
χbb
(70)
(85)
(10)
(16)
(58)
χcc
(62)
(75)
(96)
(71)
32.829(12)
RMS
0.0014
0.0016
0.0017
0.0018
0.0015

17. Some Observations κ ranges from -0.92 – -0.90
Δ ranges from – amu·Å2
typical of a planar molecule in which out-of-plane vibrational contribution is dominant
The rotational constants of 3 singly substituted isotopologues are used to locate the positions of 3 atoms.

18. Substitution Structure
CHFCHCl--- HCCH
|a|/Å
0.3758(40)
1.4935(10)
(48)
|b|/Å
1.2627(12)
1.1668(13)
0.1631(92) + + - + - b Cl C C a C C C

19. Fit to Moments of Inertia
Three geometric parameters are required to describe the structure of the complex
Fit parameters to Ia and Ic of each of the six isotopologues, assuming the structures of CHFCHCl and HCCH remain unchanged upon complexation. a b
3.076(21) Å
2.8644(23) Å
87.54(34)o Cl C H F
62.4(12)o

20. Chlorine Quadrupolar Coupling
Assuming no efg perturbation upon complexation, one of the principal efg axes should lie more or less along the C-Cl bond.
Angle between C-Cl bond and a axis
From χ tensor of CHFCH35Cl---HCCH
91.95o
From fit to inertial data
89.61o

21. Chloroethylene---HCCH Complexes
3.076(21) Å
2.8644(23) Å
62.4(12)o
3.02(1) Å
88.6(2)o
58.5(6)o
2.93(1) Å
Experimental structures Å
86.50o
57.84o Å Å Å
61.74o
85.67o
Ab initio minimum energy structures

22. Chlorofluoroethylene---HCCH Complexes
3.076(21) Å
2.8644(23) Å
62.4(12)o
124.30(70)o
2.623(11) Å
52.82(28)o
2.977(17) Å
HCCH binds to chlorine when only side binding is allowed
HCCH binds to fluorine when only top binding is allowed

23. (Z)-1-Chloro-2-fluoroethylene---HX Complexes
3.076(21) Å
2.8644(23) Å
62.4(12)o Å Å
26.00o
109.99o
Red: Most negative electric potential Blue: Most positive electric potential
Minimum energy structure predicted by ab initio calculations for the dimer with HF
Experimental structure of the dimer with HCCH

24. Summary
The rotational spectra of six isotopologues of (Z)-1-chloro-2-fluoroethylene---HCCH have been observed and analyzed.
HCCH interacts with the Cl and H atoms at one end of the double bond instead of the F and H atoms at the other end of the double bond. This bonding motif is different from that observed in all other chlorofluoroethylene---HX dimers.
The different binding modes can be explained by different steric requirements for F and Cl in the chlorofluoroethylene dimers

25. Acknowledgements National Science Foundation for providing funding
Thank you