Determination of the Structure of
Cyclopentanone and
Argon and Neon Cyclopentanone van der Waals
Complexes
40Ar
36Ar
20Ne
22Ne
18O
99.6% 0.33% 90.5% 9.2% 0.21%
Wei Lin*, Andrea J. Minei #, Andrew H. Brooks,
Dan Frohman, Chinh H.Duong, Smitty Grubbs,
Stewart E. Novick and Wallace C. Pringle
Department of Chemistry, Wesleyan University,
Middletown, CT
*Department of Chemistry
University of Texas at Brownsville, TX
#Chemistry Department, College of Mount Saint Vincent, Riverdale,
NY
Previously Studied van der Waals
Complexes
• Thietane, oxetane, cyclobutanone, methylene
cyclobutene, cyclopentene oxide, chloro-cyclobutane
Equilibrium Structure of argon-methylene cyclobutene
rm(1) position of argon in methylene cyclobutane is in ac
plane
J.Mol.Spectrosc,200
8
a
c
(r0 position from A0, B0, C0 is 0.51Å toward you from ac plane)
Rare gas (guest) forms a van der Waals complex with a ring
molecule (host) in a collision free supersonic jet at T ~ 2K
a. Where does it attach and why? Lewis base search for pair
acceptor (positive part of host)
b. The rare gas undergoes 3 very large amplitude motions in its
ground state: vdW stretch, cross ring bend and another bend
usually in the plane perpendicular to the ring plane.
c. The position of the rare gas as determined from an ab initio
calculation is at the equilibrium position, re . That is at the
minimum in the potential energy for each vibration.
d. In rings, this rare gas position is often in the ac plane if the ring.
e. The position of the rare gas determined from the observed
rotational constants, A0, B0, C0, is not the same as the
equilibrium position due to the averaging of the moment of
inertia over these very large ground state wavefunctions:
<ψ(0)|1/mr2 |ψ(0)>: this leads to ro structure
Ring Strain and Cross Ring Distance
• Five-membered ring angle of 108° much closer to the
unstrained sp3 hybridized 109.5° angle than the fourmembered ring angle of 90°
• Distance between cross ring CH2 groups, d(C-C)
– 4 membered ring 2.22Å cyclobutanone
– 5 membered ring 2.48Å cyclopentanone
C
C
C
C
Ring Puckering and Rare Gas
Quenching
• Ring angle strain is increased if ring is non-planar
(108 or 90 is decreased in non-planar ring)
• Torsional eclipsed repulsion is reduced if ring
becomes non-planar (eclipsed become staggered)
• Non-planar rings often have a double minimum
inversion vibration: competition tween ring strain
{planar} and torsional forces {non-planar}
• Some 5-membered rings exhibit pseudo-rotation
• Complexation with rare gas destroys symmetry of
double minimum and quenches puckering
Cross ring bending of rare gas with an amplitude
of approximately 1.0Å leads to spectrum for the
13C complex with a natural abundance of 2% due
β
to the equivalence of the isotopologues in 4
membered rings
Cβ
Cβ
Cyclopentanone
• Five-membered ring
• Ring structure previously
determined by Kim &
Gwinn (1969)
• Early microwave by
JHBurkhalter, JCP 1955
α
β'
β
γ
γ'
Cyclopentanone Conformers
Bent, Cs
μa , μc
CS
plane
C2 axis
Twisted, C2
μa only
•
•
•
•
Rotational structure determined to be twisted by Kim & Gwinn
Observed a type transitions only
Lack of c type transitions rules out bent conformation
We confirmed twisted structure by 13C and 18O Kraitchman
analysis, 2nd moments and pairs of equivalent 13C in the ring
Spectroscopic Constants for
Cyclopentanone
All 12C
Kim et al1
α - 13C
β - 13C
γ - 13C
18O
A/MHz
6620.0563(9)
6621(2)
6620.4472(4)
6490.6778(4)
6570.9023(6)
6620.0401(3)
B/MHz
3351.5304(3)
3351.54(3)
3336.0047(3)
3351.2183(3)
3304.4345(4)
3177.6996(3)
C/MHZ
2410.4155(3)
2410.40(3)
2402.4290(3)
2393.2710(3)
2380.7552(4)
2319.1607(3)
ΔJ/kHz
0.3369(50)
n.r.
0.28(1)
0.26(1)
0.27
0.259(8)
ΔK/kHz
0.455(95)
n.r.
0.462
0.462
0.462
0.462
ΔJK/kHz
1.1567(214)
n.r.
1.162
1.162
1.162
1.162
δJ/kHz
0.05410(83)
n.r.
0.05412
0.05412
0.05412
0.05412
δK/kHz
0.4671(155)
n.r.
0.472
0.472
0.472
0.472
N
43
n.r.
16
16
17
15
σ/kHz
4
n.r.
2
2
3
2
1Kim,
H; Gwinn, W.D.; J. Chem. Phys. 51, 1815-1819 (1969)
at the values for the all 12C isotopomer
2Fixed
Planar Moments for
Cyclopentanone isotopes
(Σmb2 from ac plane)
Isotopologue
Planar Moment Pbb
Parent all 12 C – 16 O
66.388
Carbonyl 13 C – 16 O
66.383
Carbonyl 12 C – 18 O
66.388
Out of ac plane 13 Cβ
67.854
Cartesian Coordinates of Cyclopentanone
rs
structure1
a
b
c
O
α-C
β1-C
β 2-C
γ1-C
γ2-C
1
2.053
0.841
0.05i
0.05i
1.448
1.448
0.02
0.05i
1.232
1.232
0.732
0.732
0.02i
0.01
0.132
0.132
0.236
0.236
Absolute values reported
re
B3LYP/6-311+G
a
b
c
2.0557
0
0
-0.849
0
0
0.044 1.234 0.125
0.044 -1.234 -0.125
1.455 0.740 -0.221
1.455 -0.740 0.221
All isotopolog
mixed rs r0 re
a
b
-2.054
-0.846
0.049
0.049
1.451
1.451
0
0
1.233
-1.233
0.734
-0.734
c
0
0
0.141
-0.141
-0.238
0.238
Spectroscopic Constants for 40Argon Cyclopentanone
5 different 13C isotopes:
argon on one side of
ring removes
equivalence of β and γ
13C pairs
All 12C
α -13C
β 1 -13C
β 2 -13C
γ 1 -13C
γ 2 -13C
18
A (MHz)
2611.6688(2)
2600.4210(3)
2590.5509(3)
2592.4591(4)
2592.0986(5)
2581.0381(2)
2505.3269(4)
B (MHz)
C (MHz)
1112.30298(6)
971.31969(6)
1110.5405(3)
968.4116(2)
1105.884(4)
969.3973(3)
1104.7614(4)
968.0575(2)
1100.8140(6)
961.4532(4)
1107.2212(2)
964.5622(2)
1111.6130(5)
955.6824(3)
ΔJ (kHz)
ΔK (kHz)
ΔJK (kHz)
2.5732(4)
1.321(8)
7.151(3)
2.553(4)
1.03(1)
7.27(1)
2.534(4)
1.04(1)
7.09(2)
2.534(4)
1.17(2)
7.00(2)
2.533(7)
2.53(2)
6.43(2)
2.548(3)
1.43(1)
6.85(1)
2.491(6)
0.38(3)
7.47(2)
δj (kHz)
δk (kHz)
N
 (kHz)
0.3919(3)
4.89(1)
102
2
0.390(2)
4.88(6)
21
1
0.378(3)
4.61(8)
28
1
0.373(2)
4.70(8)
26
1
0.392(3)
4.87(9)
25
2
0.398(1)
4.67(5)
26
1
0.409(2)
5.0(1)
17
1
O
Spectroscopic Constants for 36Argon Cyclopentanone
A(MHz)
B(MHz)
C(MHz)
ΔJ (kHz)
ΔJK (kHz)
ΔJK (kHz)
δJ (kHz)
δK (kHz)
N 2a, 7b
σ(kHz)
2616.943
1178.019
1021.975
7.3
-7.3
-36.8
0.392*fixed 40Ar
4.88*
9
10
Argon Cyclopentanone
• Position of Argon in the Principal Axis System (PAS) of
Cyclopentanone (extreme Kraitchman): Δm = 40, 36
•
•
40Ar
a = 0.944Å, b = 0.804Å, c = 3.458Å
36Ar a = 0.943Å, b = 0.795Å, c = 3.459Å
Explain Extreme Kraitchman
Assumes the monomer ring is an unsubstituted isotope with
rare gas mass = 0.0
The isotopic substitution is the complex with the rare gas
mass equal to 20, 22, 36 or 40
Thus in Kraitchman analysis ΔM = mass of rare gas
And the Kraitchman Coordinates are those of the rare gas in
the Principal Axis System of the monomer ring
Differing vibrational averaging in the monomer and comlex
should make coordinates different (especially vdW bonds)
But the coordinates are nearly equal even though mass
change is 10%!
r0 argon structure-side view
r0 structure of argon complex from top: Ar b coordinate = 0.8Å PAS ring
Equilibrium Structure of Ar-CPONE from top
Observed Spectra
Ne-Cyclopentanone
• 70
20Ne
– 12C5H80 lines assigned
– 32 a-type
– 23 b-type
– 15 c-type
• 57
22Ne
– 12C5H8O lines assigned
– 29 a-type
– 28 b-type
• 21-28 lines assigned for each
20Ne – 13C12C H O isotopomer
4 8
Spectroscopic Constants for 20Ne
and 22Ne Cyclopentanone
20
12
Ne – C5H8O
22
12
Ne – C5H8O
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
70
57
/kHz
4
4
Spectroscopic Constants for 20Neon
Cyclopentanone isotopologues
20Ne
20Ne
- all 12C
α13C
20Ne
β13C
–
β’13C
20Ne
20Ne
γ13C
–
γ’13C
20Ne
2728.8120(5)
2717.011(6)
2705.776(6)
2707.349(8)
2699.844(7)
2715.460(6)
1736.5882(3)
1736.488(8)
1726.074(7)
1725.051(1)
1728.184(7)
1715.546(7)
1440.4681(3)
1437.113(6)
1439.714(5)
1437.428(7)
1429.316(6)
1425.552(4)
15.050(5)
15.00(2)
14.75(1)
14.75(2)
14.90(2)
14.72(1)
49.99(4)
49.7(7)
47.7(7)
47.7(1)
51.1(9)
54.2(7)
-13.96(3)
-13.9(8)
-13.2(7)
-13.1(1)
-15.5(7)
-16.3(5)
3.47(7)
3.44(1)
3.63(8)
3.54(8)
A/MHz
B/MHz
C/MHZ
ΔJ/kHz
ΔK/kHz
ΔJK/kHz
δJ/kHz
δK/kHz
6.53(6)
3.63(7)
3.604(3)
6.7(2)
6.2(1)
6.4(2)
6.2(2)
5.9(1)
70
26
27
21
28
23
4
2
2
3
3
1
N
σ/kHz
rs Structure of the Heavy Atoms
of the Ne-Complex
a coordinate/Å b coordinate/Å c coordinate/Å
Ne
α-C
β-C
β’-C
γ-C
γ’-C
* Imaginary
2.62
0.125
0.435
0.78
1.035
1.778
0.882
0.899
*
0
0.361
1.293
0.722
0.223
0.033
1.263
1.163
0.588
0.647
Parent vs. Complex
(compare rs bond lengths
and angles)
Bond Lengths/Å
Parent
Complex
α-β
1.498
1.56
α-β‘
1.497
1.47
β-γ
1.575
1.58
β‘-γ‘
1.575
1.56
γ-γ‘
1.538
1.55
Bond Angles/°
β
α
γ’
β’ γ
Dihedral Angles/°
Parent
Complex
Parent
Complex
β-α-β‘
111.66
110.1
β‘-α-β-γ
11
13
α-β-γ
103.66
102.2
β-α-β‘-γ‘
12
12
β-γ-γ‘
103.32
102.8
α-β-γ-γ‘
-31
-34
β‘-γ‘-γ
103.32
102.3
γ-γ‘-β‘-α
-31
-33
α-β-γ‘
103.46
105.7
β-γ-γ‘-β‘
38
41
Neon Cyclopentanone
• Position of Neon in the Principal Axis System (PAS) of
Cyclopentanone(extreme Kraitchman): Δm = 20, 22
•
•
20 Ne:
a = 0.914Å, b = 0.783Å, c = 3.260Å
22 Ne: a = 0.912Å, b = 0.787Å, c = 3.256Å
Argon vs. Neon
in PAS of monomer
Argon 12C5H8O
Neon 12C5H8O
a-axis/Å
0.95
0.91
b-axis/Å
0.80
0.78
c-axis/Å
3.46
3.26
Rare Gas
vdW
radius/Å
1.88
1.54
Conclusions
a. Argon and neon complexes with cyclopentanone form over
the beta carbon that is below the ab plane of the ring
b. Rare gas binding to one side of the ring removes the C2
symmetry of the ring and 5 unique 13C complex spectra are
observed
c. Argon 40 and 36 isotopes have almost exactly the same
extreme Kraitchman coordinates in PAS of CPONE
d. Neon 20 and 22 isotopes have almost exactly the same
extreme Kraitchman coordinates in PAS of CPONE
e. The ground state vibrational wave functions for the 3 vdW
large amplitude vibrations do not change much when the
mass of the isotopes change by 10%