Microwave Spectroscopic Investigations of the C—H…p Containing Complexes CH2F2…

Propyne and CH2ClF…Propyne

Rebecca A. Peebles, Sean A. Peebles, Cori L. Christenholz, Yasser J. Dhahir,

Anthony A. ErnstDepartment of Chemistry, Eastern Illinois University,

Charleston, IL 61920

C—H…p Interactions

Cl

F

80.0(16)°

3.122(46) Å148.7(7)°

2.724(7) Å

Sexton, et al., Phys. Chem. Chem. Phys.,12 (2010), 14263.

3.207(22) Å

101.0(1)°

3.236(6) Å

Elmuti, et al., Phys. Chem. Chem. Phys., 13 (2011), 14043.

3.293(40) Å

2.670(8) Å

153.2(5)°

81.6(14)°

Obenchain, et al., J. Phys. Chem. A, 115 (2011), 12228.

2.84(6) Å

94.9(3)°

3.363(14) Å

Obenchain, et al., in preparation.

Propyne Complexes

• New considerations– Two inequivalent C—H bond donors in propyne– Internal rotation

Possible Structures

I II III IV V

A / MHz 4650.1 5870.8 5783.0 4516.8 6482.7

B / MHz 1572.5 1422.6 1362.3 1568.9 1063.4

C / MHz 1513.1 1162.0 1118.3 1495.1 924.3

ma / D 0.01 1.53 1.66 0.01 2.58

mb / D 1.24 0.75 0.71 1.23 1.32

mc / D 0.00 0.00 0.00 0.00 0.00

Pcc / u Å2 48.0 3.2 3.2 48.0 3.2

Relative Energy / cm-1

0 27 35 58 234

Gaussian 03: MP2/6-311++G(2d,2p)

Experimental

• CH2F2…Propyne– Scanned on 480 MHz CP-FTMW– Sample: ~1.8% each CH2F2 and propyne in He/Ne

pressurized to 5.2 bar in 1 L tank – delivered to nozzle at ~2 bar

– 2000 gas and microwave pulses per frequency step– Isotopes on cavity FTMW• Enriched: CH3CCD (98% D, CDN Isotopes)• All four carbons in natural abundance

J = 3 - 2 J = 4 - 3

J = 5 - 4J = 6 - 5

AABS: Z. Kisiel, L. Pszczolkowski, I. R. Medvedev, M. Winnewisser, F.C .De Lucia, C . E. Herbst, J.Mol.Spectrosc., 233, (2005), 231.PROSPE Web SITE: Z.Kisiel, in: J. Demaison, et al. (Eds.), Spectroscopy from Space, Kluwer Academic Publishers, Dordrecht, 2001, pp.91-106.

Spectroscopic Constants

propyne Pbb 1.59 u Å2

CH2F2 Paa 46.01 u Å2

CH2F2 Pbb 8.63 u Å2

CH2F2 Pcc 1.66 u Å2

CH2F2…

CH3CCH

CH2F2…

CH3CCD

CH2F2…

CH3C13CH

CH2F2...

CH313CCH

CH2F2...13CH3CCH

13CH2F2...

CH3CCH

A / MHz 5815.5858(34) 5412.3485(36) 5669.212(15) 5809.536(16) 5732.666(16) 5810.341(16)B / MHz 1341.1191(10) 1327.4534(11) 1326.3804(7) 1324.5778(7) 1322.0696(7) 1335.0765 (7)C / MHz 1099.2040(9) 1074.9320(11) 1084.0441(9) 1087.8428(9) 1083.4602(9) 1094.9527(9)

DJ / kHz 1.805(6) 1.760(7) 1.716(19) 1.782(19) 1.742(19) 1.824(19)

DJK / kHz 20.733(32) 20.348(45) 20.733 20.733 20.733 20.733

dJ / kHz 0.3192(46) 0.3486(54) 0.3192 0.3192 0.3192 0.3192

dK / kHz 13.64(33) 12.28(39) 13.64 13.64 13.64 13.64

Pcc / u Å2 1.9832(4) 1.9693(4) 1.9839(14) 1.9805(15) 1.9861(15) 1.9827(15)

rms / kHz 1.6 2.7 4.5 4.2 2.2 2.638 lines 29 lines 8 lines 8 lines 8 lines 8 lines

Structure I: 1.59 + 46.01 = 47.60 u Å2

Structure II: 1.59 + 1.65 = 3.24 u Å2

I II

I II III

A / MHz 4650.1 5870.8 5783.0

B / MHz 1572.5 1422.6 1362.3

C / MHz 1513.1 1162.0 1118.3

ma / D 0.01 1.53 1.66

mb / D 1.24 0.75 0.71

mc / D 0.00 0.00 0.00

Pcc / u Å2 48.0 3.2 3.2

Relative Energy / cm-1

0 27 35

CH2F2-Propyne Structure

r0 rs re

3.497(1) Å3.480(2) Å3.388 Å

85.56(9)°85.84(23)°84.7°

89.61(4)°85.0°

1.060(2) Å1.060(1) Å

1.2073(10) Å1.212(5) Å

1.4596(10) Å1.452(5) Å

Lit. rs

J. L. Duncan, et al., J. Mol. Spectrosc. 46 (1973) 232.

3.170(1) Å3.097 Å

3.109(4) Å2.875 Å

r0 re

Dipole moment|M |′ |M″| Number of Measurements

313←212 0 0 9303←202 0 0 1

1 1 63 2 9

312←211 0 0 91 1 5

414←313 0 0 71 1 72 3 5

404←303 0 0 81 1 82 2 83 3 4

Dnrms = 4.1 kHz ma = 1.568(2) D mb = 0.587(2) D mc = 0.00 D mtot = 1.674(1) D

a

b 1.97 D

0.7804 D

ma = 1.568(2) Dma = 1.434 D

mb = 0.587(2) Dmb = 0.656 D

mtot = 1.674(1) Dmtot = 1.577 D

measuredprojectedmonomers

QSTARK: Kisiel, et al., Chem. Phys. Lett., 325, (2000), 523.

Next Step – CH2ClF…Propyne

I II III IV V

A / MHz 3337.7 3738.8 5715.2 3841.1 5112.4

B / MHz 1328.0 1273.5 973.5 1044.8 808.1

C / MHz 1255.2 961.5 840.6 830.0 704.0

caa / MHz 30.1 29.8 -65.7 2.2 -48.9

cbb / MHz -43.5 -65.3 29.7 -38.1 12.7

ccc / MHz 9.8 35.5 36.1 35.9 36.2

ma / D 0.26 1.90 1.38 2.59 2.24

mb / D 0.17 0.34 0.72 0.56 1.58

mc / D 1.04 0.00 0.00 0.00 0.00

Pcc / u Å2 64.7 3.2 3.2 3.2 3.2

Relative Energy / cm-1

0 116 181 310 370

Experimental

• CH2ClF…Propyne– ~1.7% of each component in He/Ne, delivered at 1.5 –

2.5 atm– Original scan on CP-FTMW – a few very weak candidate

lines– Checked these on cavity FTMW – identified a few

transitions– Further cavity FTMW searching led to assignment– Very weak transitions – seem to get weaker and weaker– Only 35Cl and 37Cl assigned

220 - 110 221 - 111

Spectroscopic ConstantsCH2

35ClF...CH3CCH Ab Initio CH237ClF...CH3CCH

A / MHz 3423.636(8) 3337.7 3385.8964(8)

B / MHz 1253.7572(25) 1328.0 1238.0102(4)

C / MHz 1200.4850(19) 1255.2 1181.5034(15)

DJ / kHz 4.61(5) -- 4.61#

DJK / kHz 10.70(11) -- 10.70#

DK / kHz -10.5(16) -- -10.5#

1.5caa 43.639(9) 45.2 33.640(18)

0.25(cbb – ccc) -11.4869(23) -13.3 -9.257(5)

cbc -40.178(20) -34.4 -31.23(10)

cab -21.913* -21.9 -19.128*

cac -10.378* -10.4 -8.742*

Pcc / u Å2 34.8637(9) 64.7 64.8683(4)

rms / kHz 7.2 (35 lines) -- 13.0 (18 lines)

Chlorine atom coordinates (Å)Ab initio:a = 1.5246 b = 0.9575 c = 0.0287Kraitchman:a = ±1.6106(9) b = ±0.9235(16) c = ±0.051(30)

Comparison of Alkyne Complexes

Cl

F

Fitted:R(≡… C) = 3.706(4) Åf(C–≡…C) = 71.1(16)°q(Cl–C…≡) = 88.3(5)°

80.0(16)°

3.122(46) Å148.7(7)°

2.724(7) Å

3.293(40) Å

2.670(8) Å

153.2(5)°

81.6(14)°

Fitted:R(≡… C) = 3.683(7) Åf(C–≡…C) = 73.9(14)°q(Br–C…≡) = 91.7(4)°

3.207(22) Å

101.0(1)°

3.236(6) Å

Fitted:R(≡… C) = 3.605(4) Åf(C–≡…C) = 73.9(9)°q(Cl–C…≡) = 91.9(3)°

2.84(6) Å

94.9(3)°

3.363(14) Å

Fitted:R(≡… C) = 3.625(9) Åf(C–≡…C) = 70.2(28)°q(F–C…≡) = 80.0(8)°

Fitted:R(≡…C) = 3.497(1) Åf(C–≡…C) = 85.56(9)°q(F–C…≡) = 89.61(4)°

3.109(4) Å

3.170(1) Å

98.2(5)°

To be determined?

What’s Next?• Complexes with aromatic p systems– Next talk! Including benzene…HCCH

Acknowledgements• Ashley Elliott, Dan Obenchain• Current Peebles group: Anu Akmeemana,

Ashley Anderton, Cori Christenholz, Rachel Dorris, Nate Ulrich

• NSF grants: RUI-0809387, RUI-1214070