Department of Chemistry *Department of Chemistry, Mt. Holyoke College, Determination of the Structure of Cyclopenteneoxide and the Argon Cyclopenteneoxide van der Waals Complex Andrea J. Minei, Jennifer van Wijngaarden*, Wallace C. Pringle, and Stewart E. Novick Department of Chemistry Wesleyan University Middletown, CT 06459 *Department of Chemistry, Mt. Holyoke College, South Hadley, MA 01075

van der Waals Complexes vdW complex a* b* c* Argon Methylene Cyclobutane 0.11 0.51 +3.62 Argon Cyclobutanone1 0.23 0.55 ±3.48 Argon Thietane 0.57 -3.79 Argon Oxetane2 0.67 0.14 ±3.5 Argon Chlorocyclobutane3 1.27 2.82 -2.52 Argon Cyclopentanone 0.95 0.80 ±3.46 Neon Cyclopentanone 0.91 0.78 ±3.26 1Munrow, M.R.;Pringle, W.C.; Novick, S.E.; J. Phys. Chem. A 103, 2256-2261 (1999) 2 Lorenzo, F.; Lessari, A.; Lopez, J.C.; Alonso, J.L.; Chemical Physics Letters 286(3,4), 272-276 (1998) 3 Subramanian, R; Szarko, J.M.; Pringle, W.C.; Novick, S.E.; J. Mol. Struct. 742(1-3) 165-172 (2005) * On the PAS of the parent molecule upon complexation with Argon or Neon

van der Waals Complexes Argon Methylene Cyclobutane Argon Cyclopentanone

Cyclopenteneoxide a b c a

Cyclopenteneoxide Experimental Conditions 0.5% Cyclopenteneoxide in Argon ~2 atm backing pressure 5-20 GHz range Isotopomers observed in natural abundance

Cyclopentenoxide Results 25 a-type transitions 21 c-type transitions a b

Spectroscopic Constants for Cyclopenteneoxide W. J. Lafferty 12C5H8O α-13C ββ’-13C γγ’-13C 18O A (MHz) 5709.38 5709.4232(9) 5699.983(5) 5614.409(1) 5665.4784(3) 5649.9182(9) B (MHz) 4541.12 4541.1209(9) 4455.8299(2) 4520.1731(4) 4512.4125(1) 4380.1364(5) C (MHz) 3248.97 3248.9878(8) 3208.3011(2) 3208.7750(3) 3226.95203(9) 3184.3642(4) ΔJ (kHz) 0.86(4) 0.86* ΔJK (kHz) 0.71(2) 0.71* ΔK (kHz) 1.03(2) 1.03* δJ (kHz) 0.150(5) 0.150* δK (kHz) 0.31(2) 0.31* N 24 46 6 7 σ (kHz) 5 1 * Fixed to the all 12C parent isotopomer

Cyclopenteneoxide Improved all 12C rotational constants Determined the 5 quartic centrifugal distortion constants Three 13C isotopomers 18O isotopomer Complete heavy atom substitution structure Accurate starting structure for the Argon complex investigation

Argon Cyclopenteneoxide Experimental Conditions 0.5% Cyclopenteneoxide in Argon gas ~2 atm backing pressure 5-20 GHz range Possible complex lines tested against Neon Isotopomers observed in natural abundance Our experimental conditions for the argon complex were roughly the same for that of cyclopenteneoxide itself The only difference was that for any candidate for the argon complex, we tested these transition against a tank of cyclopenteneoxide in neon gas to help confirm that these transitions were indeed for the argon complex

vdW Complex Results 130 frequencies observed and fit 75 strong a-type transitions 55 weak b-type transitions b

Where is Argon? a = | 0.27 | Å b = | 0.42 | Å c = | 3.91 | Å Position of Argon in the Principal Axis System (PAS) of Cyclopenteneoxide a = | 0.27 | Å b = | 0.42 | Å c = | 3.91 | Å

Spectroscopic Constants for the Argon Cyclopenteneoxide Complex   Ar-12C5H8O Ar-α13C Ar-ββ’13C Ar-γγ’13C A (MHz) 3268.2537(5) 3225.761(6)  3227.759(6) 3245.744(1) B (MHz) 993.3458(2)  988.4684(5) 988.4942(6) 990.9177(3) C (MHz) 950.4300(2)  942.3021(5) 947.7585(7) 948.1404(3) ΔJ (kHz) 2.2319(9) 2.201(4) 2.214(5) 2.2218(3) ΔJK (kHz) 14.82(1) 14.82* ΔK (kHz) 16.15(4) 16.15* δJ (kHz) 0.0940(5) 0.0940* δK (kHz) 4.90(9) 4.90* ΦJJK (kHz) 0.00063(9) 0.00063* ΦJKK (kHz) -0.0020(3) -0.0020* N 130 16  23 29 σ (kHz) 4  5 5 * Fixed to the all 12C parent isotopomer

Signs of rs Position of Argon Structure of complex in PAS of the monomer α-12C position has same Kraitchman coordinates as only one of the four α-13C positions Argon position determined c α13C a b

Argon is Below Oxygen! a = 0.27Å, b = 0.42Å, c = -3.91Å Position of Argon in the Principal Axis System (PAS) of Cyclopenteneoxide a = 0.27Å, b = 0.42Å, c = -3.91Å c a a a b

Argon Coordinates in the PAS of Cyclopenteneoxide   a (Å) b (Å) c (Å) rs 0.27 0.42 -3.91 r0 0.42  0.56 -3.88  rm(1) 0.18  0.00 -3.93  * r0 and Watson’s rm(1) calculations courtesy of Professor Zbigniew Kisiel’s programs STRFIT and PMIFST, available at    http://info.ifpan.edu.pl/~kisiel/prospe.htm

Wide Amplitude Cross Ring Motion

van der Waals Complexes  vdW complex a* b* c* Argon Methylene Cyclobutane 0.11 0.51 +3.62 Argon Cyclobutanone 0.23 0.55 ±3.48 Argon Thietane 0.57 -3.79 Argon Oxetane 0.67 0.14 ±3.5 Argon Chlorocyclobutane 1.27 2.82 -2.52 Argon Cyclopentanone 0.95 0.80 ±3.46 Neon Cyclopentanone 0.91 0.78 ±3.26 Argon Cyclopenteneoxide  0.27 0.42 -3.91 * Position of rare gas in the principal axis system of each individual molecule

rs Position of Argon X X: b b b b Equivalent 13C spectra for C=CH2 0.51 Å C=O 0.55 Å S 0.57 Å O 0.14 Å b 2.70 Å X b b b 0.80 Å b 0.42 Å Equivalent 13C spectra for isotopomers of the complex Unique 13C spectra for each isotopomer of the complex

Conclusion vdW interaction with positive atoms Lewis Acid Charge Color Legend: vdW interaction with positive atoms Lewis Acid General model