The Rotational Spectra of CyclohexeneOxide and Its Argon van der Waals Complex

DANIEL J. FROHMAN, STEWART E. NOVICK AND WALLACE C. PRINGLEWesleyan University

June 19, 2012TH05

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Motivation• Cyclohexene oxide is one molecule in a series of similar small ring

species• Similar species are cyclopentene oxide (CPO) and cyclopentanone• Argon vdW complexes of rings are simple models of the effects

influencing weak bonding (different substituent groups and ring motions (bending, puckering, etc…)

Minei, A. J,. et al. J. Phys. Chem. A 2010 114 1427

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Cyclohexene Oxide• Previously studied1,2, A, B, & C and some centrifugal distortion terms

determined for parent and 18O and 13C isotopologues2

• Unlike cyclopentene oxide has no plane of symmetry, is very asymmetric, and so each carbon is unique

• 6th carbon kinks ring near the rear• μa = 1.152 (6), μb = 0.18 (8), μc = 1.52 (1) Debye, meaning all 3 types of

transitions, a, b, and c observable but b types will be weak1

• All species observed in natural abundance

1.) Ikeda, T. K., Roger; Curl Jr., R.F. J. Mol. Spec. 1972, 44. 4592.) Sanchez, R. B., Susana; Lopez, Juan C.; Alonso, Jose L. J. Mol. Struct. 2006, 780-781. 57

Images from PMIFST

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New Results• This work refined the rotational constants and added the remaining quartic C.D. terms

through observation of many more transitions for the parent and its 13C and 18O isotopologues

• Newly reported data for the 17O isotopologue which displays hyperfine structure via electric quadrupole splitting

• Substitution structure from fitting isotopologues of use for predicting the Ar vdW complex spectra

• Fit with Ir representation and Watson A Hamiltonian with Pickett Suite of software, SPCAT and SPFIT

a b c

Cα 1.024 (1) -0.629 (2) -0.469 (3)

Cα' 0.925 (2) 0.830 (2) -0.340 (4)Cβ -0.177 (8) -1.506 (1) -0.299 (5)

Cβ' -0.383 (4) 1.511 (1) 0.000 (71)Cγ -1.309 (1) -0.794 (2) 0.471 (3)Cγ' -1.597 (1) 0.567 (3) -0.145 (10)

O (from 18O) 1.488 (1) 0.029 (51) 0.716 (2)

O (from 17O) 1.488 (1) 0.030(50) 0.716 (2)

Pickett, H. M. J. Chem. Phys. 1991, 49. 371

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17O Isotopologue• Very low natural abundance1, 0.038%, compared to 0.205% for 18O or 1.07% for 13C• Nuclear spin, I = 5/2• Very few 17O species studied in microwave and most appear to be diatomic2 or

triatomic• A similar 17O species observed is oxirane or ethylene oxide, the most simple

epoxide3

• Quadrupole coupling constants of C6H10O and oxirane are in agreement

1.) http://www.nist.gov/pml/data/comp.cfm2.) Cooke, S. et al. Phys. Chem. Chem. Phys. 2007 9 5897

3.) Creswell, R. A.; Schwendeman., R.H. Chem. Phys. Lett. 1974, 27. 4 521

Source χaa \ MHz χbb \ MHz χcc \ MHz

Oxirane (G09)† -7.57 -4.87 12.4

Oxirane Expt.3 -7.4 -5.2 12.6

CHO (G09)*† -7.602 -4.265 11.868

CHO Expt.* -7.396 -4.660 12.056

* Results transformed into PAS of oxirane

† MP2/aug-cc-pVTZ

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Sample 17O transition image from FTMW++

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Rotational Constants of C6H10OC6H10O 13CαC5H10O 13Cα'C5H10O 13CβC5H10O 13Cβ'C5H10O 13CγC5H10O 13Cγ'C5H10O

A (MHz) 3872.06776 (18) 3854.48547 (39) 3849.12952 (59) 3803.90496 (26) 3806.34495 (22) 3848.24121 (31) 3862.76410 (32)

B (MHz) 3157.39949 (18) 3132.50306 (24) 3138.13076 (36) 3155.03597 (16) 3154.29442 (13) 3119.31584 (19) 3107.34181 (19)

C (MHz) 2110.83281 (17) 2098.24163 (37) 2097.38868 (56) 2090.86635 (25) 2089.77926 (20) 2090.46696 (29) 2085.98281 (30)

ΔJ (kHz) 0.4411 (50) 0.438 (12) 0.410 (18) 0.405 (8) 0.415 (7) 0.422 (10) 0.398 (10)

ΔJK (kHz) -0.5890 (62) [-0.589] [-0.589] [-0.589] [-0.589] [-0.589] [-0.589]

ΔK (kHz) 0.8431 (50) [ 0.8431] [ 0.8431] [ 0.8431] [ 0.8431] [ 0.8431] [ 0.8431]

δJ (kHz) 0.1243 (13) [0.1243] [0.1243] [0.1243] [0.1243] [0.1243] [0.1243]

δK (kHz) 0.1598 (32) [0.1598] [0.1598] [0.1598] [0.1598] [0.1598] [0.1598]

N (lines) 53 14 14 14 14 14 14σ (kHz) 1.9 1.4 2.1 0.9 0.8 1.1 1.1

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Rotational Constants of C6H10OC6H10O C6H10

18O C6H1017O

A (MHz) 3872.06776 (18) 3843.54706 (62) 3857.29610 (19)

B (MHz) 3157.39949 (18) 3055.21625 (41) 3104.84323 (19)

C (MHz) 2110.83281 (17) 2072.84426 (69) 2091.51610 (23)ΔJ (kHz) 0.4411 (50) 0.437 (22) 0.4221 (78)ΔJK (kHz) -0.5890 (62) [-0.589] [-0.589]ΔK (kHz) 0.8431 (50) [ 0.8431] [ 0.8431]δJ (kHz) 0.1243 (13) [0.1243] [0.1243]δK (kHz) 0.1598 (32) [0.1598] [0.1598]χaa (MHz) n/a n/a 8.8555 (49)χbb (MHz) n/a n/a -4.5600 (37)χcc (MHz) n/a n/a -4.2956 (37)

N (lines) 53 12 49

σ (kHz) 1.9 2.1 1.5

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Argon Cyclohexene Oxide• vdW complex of Ar and C6H10O along with its 13C isotopologues fit

• Position of Ar determined in 4 ways: re structure, r0 structure, rs from Kraitchman substitution structure, and mixed r0, rs, re structure

• Difficult to determine Ar position, 8 possibilities and lines from 6 unique carbons• a, b, and c type transitions observed for parent and a and b for the 13C isotopologues • Unlike in HCl C6H10O complex1, the Ar avoids the negatively charged oxygen lone pair

electrons and like a Lewis base, is nearest to the most positive part of the ring, the H α and H

α’

• Unlike in Ar CPO, lack of symmetry plane contributes to Ar favoring Hα’ over Hα position

• Argon is 3.3246 Å away from Hα’ which is larger than the vdW radii sum, 2.97 Å2,3

1.) Sanchez, R. B., Susana; Lopez, Juan C.; Alonso, Jose L. J. Mol. Struct. 2006, 780-781. 572.) Bondi, A. J. Phys. Chem. 1964, 68. 4413.) Rowland, R. S. T., Robin J. Phys. Chem. 1996, 100. 7384

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Ar Position

• Expectation is for Ar to be near polarizable oxygen lone pairs or near the polar C-O bonds• Instead Ar is essentially right over the LUMO, behaving like a Lewis Base1

• Small difference in re and r0 Ar position relative to LUMO due to vibrational averaging of ring motions and vdW stretch

1.) J. Chem. Phys. 61 1 1974 pg 193 Harris, Stephen J.; Novick, Stewart E.; Klemperer, William; Falconer, Warren E.

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Fitting of Argon C6H10O• A-type transitions primarily depend

on B & C, give easily recognizable patterns

• Ab initio Ar position did not reproduce spectral patterns well due to B and C constants

• ArCPO method better predictions for B & C constants matching of predicted & experimental a-type transitions easier, patterns more recognizable

a b cCα 0.278 (5) 0.700 (2) -3.7967 (4)

Cα' 0.282 (5) 0.711 (2) -3.7931 (4)

Cβ 0.287 (5) 0.697 (2) -3.7998 (4)

Cβ' 0.286 (5) 0.694 (2) -3.7982 (4)

Cγ 0.288 (5) 0.729 (2) -3.8005 (4)

Cγ' 0.275 (5) 0.707 (2) -3.7968 (4)Ar (r0) 0.282 (5) 0.706 (2) -3.7935 (4)Ar (rs) 0.282 (5) 0.706 (2) -3.7969 (4)

Ar (re, ab initio) 0.062 0.641 -3.6350ArCPO 0.246 0.419 -3.906Ar (r0, re, rs) 0.2829 (2) 0.706 (1) -3.7929 (14)

Ar positions in monomer PAS

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Rotational Constants of ArC6H10OArC6H10O Ar13CαC5H10O Ar13Cα'C5H10O Ar13CβC5H10O Ar13Cβ'C5H10O Ar13CγC5H10O Ar13Cγ'C5H10O

A (MHz) 2146.48256 (15) 2132.9477 (17) 2133.3069 (13) 2126.2205 (28) 2124.8550 (26) 2127.6504 (17) 2120.8355 (14)

B (MHz) 908.642922 (78) 907.02475 (12) 907.15284 (10) 903.04427 (19) 904.00082 (18) 903.10894 (12) 907.04976 (10)

C (MHz) 859.003197 (84) 856.63792 (11) 857.27340 (9) 857.19975 (18) 857.91744 (16) 852.15368 (11) 854.26121 (9)

ΔJ (kHz) 1.52462 (35) 1.51755 (90) 1.51097 (71) 1.5229 (14) 1.5046 (13) 1.50222 (92) 1.50061 (72)

ΔJK (kHz) 7.2834 (21) 7.186 (19) 7.224 (15) 7.258 (30) 7.414 (28) 7.029 (19) 7.169 (15)

ΔK (kHz) -7.643 (12) [-7.643] [-7.643] [-7.643] [-7.643] [-7.643] [-7.643]

δJ (kHz) 0.05939 (18) [0.05939] [0.05939] [0.05939] [0.05939] [0.05939] [0.05939]

δK (kHz) -1.122 (29) [-1.122] [-1.122] [-1.122] [-1.122] [-1.122] [-1.122]

N (lines) 118 25 25 25 25 25 25

σ (kHz) 1.5 1.5 1.1 2.3 2.2 1.5 1.2

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Conclusion• Rotational constants for the monomer and its 13C and 18O

isotopologues refined and added to• First time reported 17O isotopologue, adds to small number of 17O

species studied via microwave reported• Argon vdW complex and its 13C isotopologues found• Argon position determined through multiple methods, located

away from oxygen and is closer to the more positive H α and H α’ near front of the ring

• Ar distance to the closest atom Hα’ is 3.3246 Å, which is larger than the vdW radii sum 2.97 Å1,2

1.) Bondi, A. J. Phys. Chem. 1964, 68. 4412.) Rowland, R. S. T., Robin J. Phys. Chem. 1996, 100. 7384

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Acknowledgements• Novick & Pringle research group members for

advice

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Acknowledgements• Novick & Pringle research group members for advice

constant C6H10O 13CαC5H10O 13Cα'C5H10O 13CβC5H10O 13Cβ'C5H10O 13CγC5H10O 13Cγ'C5H10O C6H1018O C6H10

17O C6H1017O C6H10

17O

Ia 130.51918 131.11454 131.29698 132.85797 132.77281 131.32729 130.83354 131.48768 131.02051 131.02060 131.02054

Ib 160.06182 161.33395 161.04463 160.18172 160.21938 162.01601 162.64033 165.41516 162.77596 162.77569 162.77570

Ic 239.42166 240.85839 240.95634 241.70799 241.83372 241.75417 242.27386 243.80949 241.63031 241.63056 241.63046

Paa 134.48215 135.53890 135.35199 134.51587 134.64015 136.22144 137.04032 138.86849 136.69288 136.69282 136.69281

Pbb 104.93951 105.31949 105.60435 107.19212 107.19357 105.53273 105.23353 104.94100 104.93743 104.93774 104.93765

Pcc 25.57967 25.79505 25.69264 25.66585 25.57923 25.79457 25.60001 26.54668 26.08308 26.08286 26.08289

constant ArC6H10O Ar13CαC5H10O Ar13Cα'C5H10O Ar13CβC5H10O Ar13Cβ'C5H10O Ar13CγC5H10O Ar13Cγ'C5H10OIa 235.44524 236.93928 236.89939 237.68894 237.84169 237.52920 238.29246Ib 556.19109 557.18336 557.10469 559.63934 559.04717 559.59927 557.16800Ic 588.33204 589.95649 589.51917 589.56982 589.07661 593.06098 591.59786Paa 454.53894 455.10028 454.86223 455.76011 455.14105 457.56552 455.23670Pbb 133.79309 134.85621 134.65693 133.80971 133.93557 135.49546 136.36116Pcc 101.65215 102.08308 102.24246 103.87923 103.90612 102.03374 101.93130

Planar Moments

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Getting 17O Chigg values

2

2

0

0

ccbbaacc

ccbbaacc

ccccccbbaa

ccbbaa

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MACHINE EXTERIOR

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CAVITY INTERIOR

Photo from Stew Novick

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TIMING OF MB PROPAGATION

•Nozzle injects MB into cavity parallel to MW pulse propagation•MW pulse with high Q polarizes sample, polarization decay measured, FT of data taken, doublet seen

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FID

•Resonance frequency from molecule if present, within a 1 MHz width•Fourier-Transform of free-induction decay of polarization of the radiation emitted by the molecules•FT takes time resolved data to generate frequency domain data

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FT of FID Results

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QUADRUPOLE SPLITTING

• Arises from nuclear spin greater than 1/2• 17O has nuclear spin +5/2• F=I+J, where F is tot. ang. mom., J is ang mom. w/o nuclear spin , I• splits the rot. transitions• primarily from p orbital, measures electric field gradient at nucleus

bbbbaaaa

ccbb

a

aa

Q JICJICII

IIII

IIEQH

)12(241

3

1

)12(223

:

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2261

Kang, L., Minei, A., Novick, S., et al. J. Chem. Phys. 2009 130 124317 Namiki, Kei-ichi. et al. J. Mol. Spec. 1998 191 176

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F level splitting