1. Determination of the Structure of Neon Cyclopentanone Wei Lin, Andrea J. Minei, Andrew H. Brooks, Wallace C. Pringle, Stewart E. Novick Department of Chemistry Wesleyan University Middletown, CT 06459

2. Introduction Series of Argon four membered ring van der Waals complexes previously studied in our group Large amplitude cross ring motion

3. Motivation Five-membered rings Cyclopentanone rotational structure determined by Kim & Gwinn (1969) Argon Cyclopentanone rotational structure determined in our group No cross ring motion observed Lighter, smaller, less polarizable atom Neon Cyclopentanone

4. Cyclopentanone Conformers bent twisted Cyclopentanone structure determined as twisted by Kim and Gwinn Confirmation of twisted structure determined by 13 C isotopic substitution

5. Experimental Setup 0.5% Cyclopentanone (99+%, Aldrich) in Neon gas Backing pressure of 2 atmospheres Scanning region between 6 and 23 GHz Isotopic species observed in natural abundances (~9% 22 Ne, ~1% 13 C, ~0.2% 18 O)

6. Predicted Spectra Cyclopentanone as accurate starting structure If similar to Argon Cyclopentanone Strong a, b-type transitions Weak c-type transitions

7. Observed Spectra 70 20 Ne – 12 C 5 H 8 0 lines assigned 32 a-type 23 b-type 15 c-type 57 22 Ne – 12 C 5 H 8 O lines assigned 29 a-type 28 b-type 21-28 lines assigned for each 20 Ne – 13 C 12 C 4 H 8 O isotopomer

8. Analysis H. M. Pickett’s program Fit 3 rotational constants and 5 quartic centrifugal distortion constants to semi rigid rotor Hamiltonian in I r representation using Watson A reduction

9. Results Strong a, b-type transitions Weak c-type transitions Dipole moment mostly along a and b axes Carbonyl bond dipole moment primarily on ab plane of the complex Isotopes of Neon Direct determination of Neon position

10. Neon Cyclopentanone Spectroscopic Constants 20 Ne – 12 C 5 H 8 O 22 Ne – 12 C 5 H 8 O A/MHz 2728.8120(5)2707.7492(6) B/MHz 1736.5882(3)1658.3352(4) C/MHz 1440.4681(3)1381.4216(3)  J /kHz 15.050(5)13.883(5)  JK /kHz -13.96(3)-7.01(3)  K /kHz 49.99(4)39.29(3)  J /kHz 6.53(6)8.64(7)  K /kHz 3.604(3)3.175(2) N 7057  /kHz 44

11. Structure α β β’β’ γ’γ’ γ

12. Spectroscopic Constants for Carbon and Oxygen Isotopomers 20 Ne - α 13 C 20 Ne - β 13 C 20 Ne - β’ 13 C 20 Ne - γ 13 C 20 Ne - γ’ 13 C 20 Ne - 18 O A/MHz2717.011(6)2705.776(6)2707.349(8)2699.844(7)2715.460(6) I B/MHz1736.488(8)1726.074(7)1725.051(1)1728.184(7)1715.546(7) N C/MHz1437.113(6)1439.714(5)1437.428(7)1429.316(6)1425.552(4) P  J /kHz 15.00(2)14.75(1)14.75(2)14.90(2)14.72(1) R  JK /kHz -13.9(8)-13.2(7)-13.1(1)-15.5(7)-16.3(5) O  K /kHz 49.7(7)47.7(7)47.7(1)51.1(9)54.2(7) G  J /kHz 3.63(7)3.47(7)3.44(1)3.63(8)3.54(8) R  K /kHz 6.7(2)6.2(1)6.4(2)6.2(2)5.9(1) E N2627212823 S  /kHz 22331 S

13. r s Structure of the Heavy Atoms of the Complex a coordinate/Å b coordinate/Å c coordinate/Å Ne2.620.8820.223 α-C0.1250.8990.033 β-C0.4350*0* 1.263 β’-C0.780.3611.163 γ-C1.0351.2930.588 γ’-C1.7780.7220.647 * Imaginary

14. Parent vs. Complex Bond Lengths/Å ParentComplex α-β1.4981.56 α-β‘1.4971.47 β-γ1.5751.58 β‘-γ‘1.5751.56 γ-γ‘1.5381.55 Dihedral Angles/° ParentComplex β‘-α-β-γ1113 β-α-β‘-γ‘12 α-β-γ-γ‘-31-34 γ-γ‘-β‘-α-31-33 β-γ-γ‘-β‘3841 α β β’β’ γ’γ’ γ Bond Angles/° ParentComplex β-α-β‘111.66110.1 α-β-γ103.66102.2 β-γ-γ‘103.32102.8 β‘-γ‘-γ103.32102.3 α-β-γ‘α-β-γ‘103.46105.7

15. Structure Determination Position of Neon in the Principle Axis System (PAS) of Cyclopentanone a=0.91 Å, b=0.78 Å, and c=3.26 Å

16. Position of Argon and Neon in the Principal Axis System of the Cyclopentanone vdW Complex Argon C 5 H 8 ONeon C 5 H 8 O a-axis/Å0.950.91 b-axis/Å0.800.78 c-axis/Å3.463.26 Rare Gas vdW radius/Å1.881.54

17. Cross Ring Motion? No cross ring motion observed Neon tightly bound enough to minimize cross ring motion No plane of symmetry in twisted structure No equivalent carbons All 13 C isotopomers will be unique Asymmetry of Neon position Neon prefers β’-C(down) side of the ring Similar ring motion to the Argon complex

18. Future Work Argon Cyclopentene Larger Ring Structure van der Waals Complexes Fluorinated Radicals Interstellar Molecules