Comparison of 2,3-Dibenzofuran and 1,3Benzodioxole Using Rotationally
Resolved Electronic Spectroscopy in the
Gas Phase
Jessica A. Thomas, Leonardo AlvarezValtierra, and David W. Pratt
University of Pittsburgh
Introduction
2,3-Dihydrobenzofuran (HBF)
1,3-Benzodioxole (BDO)
• HBF: Predicted contain non-planar 5membered ring
• BDO: Predicted to contain a planar 5membered ring
HBF: Vibrationally Resolved Electronic Spectrum
0
00
+110.4
+164.8
Bands studied in High Resolution:
+157.7
34950
-1
Frequency (cm )
35150
Rotationally Resolved Electronic Spectroscopy
HBF: Rotationally Resolved Electronic Spectrum
Origin Band
Origin
A” (MHz)
3657.6(1)
B” (MHz)
1557.7(1)
C” (MHz)
1112.2(1)
ΔI” (amu Å2)
-8.20
A’ (MHz)
3528.1(1)
B’ (MHz)
1551.6(1)
C’ (MHz)
1094.4(1)
ΔI” (amu Å2)
-7.19
Band
type:
34,962.2
a/b/c
-1 -1
0.7 cm(cm
50/50/0 Frequency
)
34,965.1
HBF Rotationally Resolved Spectra of Excited Bands
+110.4
A” (MHz)
B” (MHz)
C” (MHz)
35072.5
Frequency (cm-1)
0.7 cm-1
35075.7
+110.4
3663.5(1)
1558.8(1)
1112.1(1)
ΔI” (amu Å2) -7.72
A’ (MHz)
3533.3(1)
B’ (MHz)
1554.8(1)
C’ (MHz)
1096.3(1)
ΔI’ (amu Å2) -7.10
Band type: 50/50/0
a/b/c
HBF Rotationally Resolved Spectra of Excited Bands
+157.7
+157.7
A” (MHz)
3661.1(1)
B” (MHz)
1558.0(1)
C” (MHz)
1111.4(1)
ΔI” (amu Å2) -7.69
35120.3
Frequency (cm-1)
35122.8
A’ (MHz)
3525.9(1)
B’ (MHz)
1556.3(1)
C’ (MHz)
1096.5(1)
ΔI’ (amu Å2) -7.17
0.7
cm-1
Band type:
a/b/c
50/50/0
HBF Rotationally Resolved Spectra of Excited Bands
+164.8
A” (MHz)
B” (MHz)
C” (MHz)
35127.0
Frequency (cm-1)
35128.2
+164.8
3660.0(1)
1557.4(1)
1111.6(1)
ΔI” (amu Å2) -7.93
A’ (MHz)
3535.0(1)
B’ (MHz)
1554.7(1)
C’ (MHz)
1096.9(1)
ΔI’ (amu Å2) -7.31
0.7 cm-1
Band type:
a/b/c
50/50/0
2,3-Dihydrobenzofuran
• All bands exhibit a/b
hybrid type spectra
• Inertial defect is less
negative in the
excited state
– i.e. The molecule
becomes more planar
upon excitation
Band ΔI”
ΔI’
Origin
-8.20
-7.19
+110.4
-7.72
-7.10
+157.7
-7.69
-7.17
+164.8
-7.93
-7.37
Introduction
2,3-Dihydrobenzofuran (HBF)
1,3-Benzodioxole (BDO)
• HBF: Predicted contain non-planar 5membered ring
• BDO: Predicted to contain a planar 5membered ring
BDO: Vibrationally Resolved Electronic Spectrum
Bands studied in high resolution:
+101.5
+204.2
0
00
+382.4
+353.9
J. Laane, J. Phys. Chem. A (2000), 104, 7715.
BDO: Rotationally Resolved Electronic Spectrum
Origin
34783.7
Frequency (cm-1)
0.7 cm-1
34787.1
Rotational Constants: Origin
Ground State
Experimental
Microwavea
A” (MHz)
3794.3(1)
3795.00
B” (MHz)
1621.3(1)
1621.032
C” (MHz)
1148.1(1)
1147.979
ΔI” (amu Å2)
-4.70
-4.70
Electronicb
Excited State
A’ (MHz)
3627.9(1)
3628.448
B’ (MHz)
1629.1(1)
1628.410
C’ (MHz)
1136.5(1)
1136.453
ΔI’ (amu Å2)
-4.86
-4.94
Band type: a/b/c
100/0/0
-
aMeyer
and coworkers, Molec. Phys. 80, 1297 (1993)
bCastelucci
and coworkers, Chem. Phys. Lett. 385, 304 (2004).
Experimental Results
Origin
+101.5
+204.2
+353.9
+382.1
A”
3794.3
3791.7
3794.4
3794.9
3792.3
B”
1621.3
1621.2
1621.2
1621.1
1621.0
C”
1148.1
1148.1
1148.1
1148.1
1148.1
ΔI”
-4.70
-4.83
-4.71
-4.73
-4.85
A’
3627.9
3617.9
3614.8
3616.3
3616.1
B’
1629.0
1631.5
1631.7
1629.9
1630.5
C’
1136.5
1138.8
1139.3
1139.9
1138.6
ΔI’
-4.86
-5.69
-5.93
-6.39
-5.86
Band type:
a/b/c
100/0/0
100/0/0
100/0/0
100/0/0
100/0/0
Pucker vs. Flap
Inertial defect may be accounted for by
pucker or flap of 5-membered ring
Pucker
Flap
BDO: Analysis of Inertial Defect
Using Calculateda Change in Pucker Angle
Pucker Angle
-3.00
Inertial Defect
0
5
-4.00
-5.00
φ
aMP2/6311g(d,p)
bDetermined
cGraph
Angle (φ)c
-4.86
15.2º
-5.69
18.8º
-5.93
19.7º
-6.39
21.3º
Band
-5.86
ΔI” (expt’l)
19.4º
Angle (φ)b
Origin
-4.70
13.1º
+101.5
-4.83
13.8º
+204.2
-4.71
13.1º
+353.9
-4.73
13.2º
+382.1
-4.85
13.9o
and cis/6311g(d,p)
by graph above
not shown
ΔI’10(expt’l)
15
BDO: Analysis of Inertial Defect
Using Calculated Change in Flap Angle
-4.00
10
11
12
13
14
15
16
18
19
20
ΔI’ (expt’l) Angle (φ)b
-4.50
Inertial Defect
17
-4.86
15.0º
-5.69
18.7º
-5.93
19.6º
-6.39
21.3º
-5.00
-5.50
-6.00
Flap Angle
φ
aMP2/6311g(d,p)
bDetermined
cGraph
Band
-5.86
ΔI” (expt’l)
19.3º
Angle (φ)a
Origin
-4.70
14.2º
+101.5
-4.83
14.9º
+204.2
-4.71
14.2º
+353.9
-4.73
14.3º
+382.1
-4.85
15.0º
and cis/6311g(d,p)
by graph above
not shown
Pucker vs. Flap
Band Freq.
Pucker, S0
Flap, S0
Pucker, S1
Flap, S1
Origin
13.1º
14.2º
15.2º
15.0º
+101.5
13.8º
14.9º
18.8º
18.7º
+204.2
13.1º
14.2º
19.7º
19.6º
+353.9
13.2º
14.3º
21.3º
21.3º
+382.1
13.9o
15.0º
19.4º
19.3º
Pucker
Flap
1,3-Benzodioxole
• Pure a-type spectra for all bands
• More planar than HBF in ground state
Origin
bands
ΔI”
ΔI’
HBF
-8.20
-7.19
BDO
-4.70
-4.86
• Inertial defect is more negative in excited state
compared with ground state (opposite of HBF)
– i.e. The molecule becomes less planar upon excitation
Anomeric effect due to -O-CH2-O- ?
The anomeric effect was first used to describe
the axial configuration in sugars
Two models:
1. Repulsive n-n interactions are minimized
2. Stabilizing interaction between a lone pair on one oxygen atom
and the antibonding σ* orbital of the other C-O bond
Anomeric Effect in BDO
b
a
planar
puckered
Laane, J. Phys. Chem. A 104, 7715 (2000)
Summary
• HBF: less planar in ground than excited state
• BDO: more planar in ground than excited state
and more planar than HBF in both states
• Do BDO bands +101.5 and +382.4 originate in
the ground state?
• In BDO, is the anomeric effect is stronger in the
excited state leading to less planarity and
smaller dihedral angles?
Current and Future Work
• Calculations for the twisted configuration and
hybrids of pucker/fold/twist
• Spectra of deuterated molecules
Acknowledgements
• Members of the Pratt group for assistance in
the lab and helpful conversations: especially
Philip Morgan and Diane Mitchell
• NSF for funding
2,3-HBF: Molecular Orbitals and Transition Moment
HOMO
HOMO-1
63%
LUMO+2
a- and b-type
29%
LUMO
1,3-BDO:Molecular Orbitals and Transition Moment
HOMO
LUMO
63%
a
a-type
b
HOMO-1
31%
a-type
LUMO+1
2,3-HBF Experimental Results
origin
+110.4
+157.7
+164.8
A’ (MHz)
3657.6
3663.5
3661.1
3660.0
B’ (MHz)
C’ (MHz)
1557.7
1112.2
1558.8
1112.1
1558.0
1111.4
1557.4
1111.6
-8.20
-7.72
-7.69
-7.93
A” (MHz)
3528.1
3533.3
3525.9
3535.0
B” (MHz)
1551.6
1554.8
1556.3
1554.7
C” (MHz)
1094.4
1096.3
1096.5
1096.9
-7.19
-7.10
-7.17
-7.31
50/50/0
50/50/0
50/50/0
50/50/0
ΔI’ (amu Å2)
ΔI” (amu Å2)
Band type:
a/b/c
1,3-BDO Rotationally Resolved Spectrum of Origin
+101.5 cm-1
34885.3
Frequency (cm-1)
0.7
cm-1
34889.0
Expt’l
Casteluccia
A’ (MHz)
3617.9(1)
3621.45
B’ (MHz)
1631.5(1)
1629.98
C’ (MHz)
1138.8(1)
1138.00
ΔI’ (amu
Å2)
-5.69
-5.68
Band type:
a/b/c
100/0/0
aCastelucci
304 (2004).
-
and coworkers, Chem. Phys. Lett. 385,
1,3-BDO Rotationally Resolved Spectrum of Origin
+204.2 cm-1
34988.0
Frequency
(cm-1)
34991.2
Expt’l
Casteluccia
A’ (MHz)
3616.3(1)
3615.11
B’ (MHz)
1631.7(1)
1631.57
C’ (MHz)
1139.3(1)
1139.34
ΔI’ (amu Å2)
-5.93
-5.97
Band type:
a/b/c
100/0/0
aCastelucci
0.7
cm-1
304 (2004).
-
and coworkers, Chem. Phys. Lett. 385,
1,3-BDO Rotationally Resolved Spectra of Excited
Bands
+353.9
35138.0
+382.1
Frequency (cm-1)
0.7 cm-1
35138.6
35165.9
Frequency (cm-1)
0.7 cm-1
35169.6
13BDO: Vibrationally Resolved
4.5
4
+101.5
+382.1
+353.9
+204.2
Origin
+290.4
3.5
3
2.5
2
1.5
1
0.5
0
34700
34800
34900
35000
35100
35200
35300
2,3-HBF Vibrational Motions
Experimental
Frequencies (cm-1)
101.5
204.2
290.4
Same mode?
Calculated
Frequencies (cm-1)
Using
MP2/6311+g(d,p)
94.337
144.207
224.074
353.9
337.474
382.1
364.392
393.330
2,3-HBF Vibrational Motions
Experimental
Frequencies
110.4
Calculated
Frequencies
Using
MP2/6311g+(d,p)
129.9
157.7
147.6
164.8
214.3