1. Determination of the Structures of Cyclopentanone and of the Argon Cyclopentanone van der Waals Complex
Andrew H. Brooks, Wei Lin, Wallace C. Pringle and Stewart E. Novick
Department of Chemistry, Wesleyan University,
Middletown, CT 06459

2. Positions of Argon in Ar Four-membered Ring Complexes studied in this lab

3. Argon Methylene Cyclobutane (RC08)
Ar: a = 0.11Ǻ b = 0.51Ǻ c = 3.62Ǻ
(on the PAS of Methylene Cyclobutane)

5. Experimental conditions
Fourier Transform Microwave spectrometer
0.5% Cyclopentanone in Ar
0.3 atm backing pressure
13C and 18O isotopomers were measured in natural
abundance

6. Four-membered vs Five-membered rings
Ring strain is much less for a five-membered ring than for a four-
membered ring, giving rise to a nonplanar molecule
ADD PICTURES W/ANGLES!

7. Cyclopentanone
Bent
Twisted

8. Spectroscopic Constants for Cyclopentanone

9. Cartesian Coordinates of Cyclopentanone

10. Cyclopentanone
All 12C isotopomer and three 13C isotopomers,
improved spectroscopic constants
New 18O isotopomer,
complete heavy-atom substitution structure
Accurate starting structure for Ar cyclopentanone investigation

11. Ar Cyclopentanone

12. LAS program Programmed by Aaron J. Schoeffler (from Art Maki’s ASY7)
Takes a set of observed but unassigned rotational lines and determines assignments using any combination of lines and a range of rotational constant values set by an initial prediction and a tolerance parameter.
First success of LAS program!

13. Spectroscopic Constants for Argon Cyclopentanone

14. (on the PAS of cyclopentanone)
Where is Argon?
Ar: a = 0.95Ǻ b = 0.80Ǻ c = 3.46Ǻ
(on the PAS of cyclopentanone)
Five 13C isotopomers at 1% abundance, one 18O at 0.2% abundance

15. Positions of Argon in Ar Four-membered Ring Complexes studied in this lab

17. What’s Next
Ne Cyclopentanone van der Waals Complex (RH09)
Ar Cyclopentene van der Waals Complex
Larger rings?
Ar Tropolone van der Waals Complex (RH10)

18. Summary
Complete substitution structures from FTMW
spectra of all 12C and 13C, 18O singly substituted
cyclopentanone and argon cyclopentanone