A Study of 4,4 ΄ -Dimethylaminobenzonitrile by Chirped-Pulsed Fourier Transform Microwave...
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Transcript of A Study of 4,4 ΄ -Dimethylaminobenzonitrile by Chirped-Pulsed Fourier Transform Microwave...
A Study of 4,4΄-Dimethylaminobenzonitrile by Chirped-Pulsed Fourier Transform
Microwave Spectroscopy
Ryan G. Bird, Valerie J. Alstadt, and David W. Pratt
University of Pittsburgh
Justin L. Neill and Brooks H. Pate
University of Virginia
Prelude to Charge Transfer• DMABN is widely known
model for excited state charge transfer
• Charge transfer facilitated by twisting amino nitrogen
• Determine electronic density around amino nitrogen using quadrupole coupling terms
• DMABN = 2 nitrogen nuclei– Simplified model; DMA = 1
nucleusE. Lippart, W. Lüder, and H. Boos, in the Proceedings of the 4th International Meeting on Advances in Molecular Spectroscopy (1959), A. Mangini, ed., Pergamon Press, Oxford, 1962, pgs. 443-457.
CP FTMW Spectrometer
MW Synthesizer
Arbitrary Waveform Generator
Fourier Transform
Free Induction Decay
Chirped Pulse240 MHz
500 MHzDigitizer(10 Gs/s)
Spectrum of N,N΄-Dimethylaniline
10000 avg~500 MHz CP
Inversion of DMA
505←404
1000 avg10 MHz CP
0+
0-
0-
0+
Rotational Constants DMA
This work Lister1 mp2/6-31+g(d)
A(0+) (MHz) 3500.315(103) 3500.39 3500.042
B(0+) (MHz) 1226.667(4) 1226.646 1224.151
C(0+) (MHz) 923.345(3) 923.328 923.877
A(0-) (MHz) 3500.779(119) 3499.88
B(0-) (MHz) 1226.646(5) 1226.590
C(0-) (MHz) 923.609(5) 923.645
ΔI (amu Å2) -9.1 -9.0 -10.2
Lines 95
1Cervellati, R.; Borgo, A. D.; Lister, D. G. Journal of Molecular Structure 1982, 78, 161-167.
Barrier to Inversion
Aniline1 N-methylaniline1 N,N-dimethylaniline
Inversion angle (φ) 37 ~20 22
V2 barrier (cm-1) 526 167 24 + 3
1Cervellati, R.; Esposti, A. D.; Lister, D. G.; Palmieri, P. Journal of Molecular Structure: THEOCHEM 1985, 122, 173-177.
ΔE = 4.5 + 0.5 cm-1
I is the integrated peak area
g is the statistical weight
F = ћ2/2Ir
Ir is the reduced moment of inertia of the inversion motion
N,N΄-Dimethylaminobenzonitrile2 – 8 GHz190,000 avg9 GHz CP
6 – 18 GHz10,000 avg~500 MHz CP
DMABN Constants
This work Endo1 LIF2 M052x
A (MHz) 3469.2(9) 3469.99 3470.3 3469.37
B (MHz) 578.583(2) 578.581 578.7 580.99
C (MHz) 499.612(2) 499.613 499.7 500.97
ΔI (amu Å2) -7.61 -7.58 -7.56 -6.73
Lines 293
1Kajimoto, O.; Yokoyama, H.; Ooshima, Y.; Endo, Y. Chemical Physics Letters 1991, 179, 455-459.2Nikolaev, A. E.; Myszkiewicz, G.; Berden, G.; Meerts, W. L.; Pfanstiel, J. F.; Pratt, D. W. Journal of Chemical Physics 2005, 122, 1-10.
Quadrupole Splitting in DMABN2 – 8 GHz 6 – 18 GHz
313←212 909←808
Amine Quadrupole Coupling
Compound Aniline1 DMA DMABNAmine N
χaa (MHz) 2.34(6) 2.58(3) 2.54(33)
χbb (MHz) 1.86(6) 2.80(6) 2.80(13)
χcc (MHz) -4.20(6) -5.39(6) -5.33(13)
Inversion Angle (deg) 37 22 6
1Hatta, A.; Suzuki, M.; Kozima, K. Bull. Chem. Soc. Jap. 1973, 46, 2321-3.
Lone pair density
Inversionangle
Hyperconjugation
H
H
HN
-
+
C C
+
-
+
-
π-π donation π-π donation
N-
+
Nitrile Quadrupole Coupling
DMABN Benzonitrile1 Ethyl Cyanide2
Nitrile N
χaa (MHz) -4.11(30) -4.23738(36) -3.309(33)
χbb (MHz) 2.40(13) 2.2886(11) 1.265(13)
χcc (MHz) 1.71(13) 1.9488(11) 2.044(20)
1Wohlfart, K.; Schnell, M.; Grabow, J. U.; Küpper, J. Journal of Molecular Spectroscopy 2008, 247, 119-121.2Li, Y. S.; Harmony, M. D. The Journal of Chemical Physics 1969, 50, 3674-3677.
C N-
+ +
-
π-π donation
Townes and Dailey Populations1
Aniline2 DMA DMABN
χzz (MHz) 2.38 2.72 2.55
χxx(MHz) 1.86 2.8 2.8
χyy(MHz) -4.24 -5.52 -5.34
Nz 1.25 1.29 1.4
Nx 1.28 1.28 1.3
Ny 1.76 1.98 2.0
X
Y
1Townes, C. H.; Dailey, B. P. The Journal of Chemical Physics 1949, 17, 782-796.2 Lister, D. G.; Tyler, J. K.; Høg, J. H.; Larsen, N. W. Journal of Molecular Structure 1974, 23, 253-264.
Aniline → DMA → DMABN
• Decrease in inversion angle and increase in amine χcc coupling term
• Caused by increase in electronic density around amine nitrogen
• Electronic density stabilized through hyperconjugation
• Increased density facilitates charge transfer• Quadrupole terms of excited state??
Acknowledgements
Pratt Group: Pate Group:
Dr. David Pratt Dr. Brooks PateJustin Young Justin NeillA.J. Fleisher Matt MucklePhil Morgan Daniel ZaleskiJessica ThomasCasey Clements
Quadrupole CouplingCompound Aniline1 DMA DMABN Benzonitrile2 Ethyl Cyanide3
Amine N
χaa (MHz) 2.34(6) 2.58(3) 2.54(33)
χbb (MHz) 1.86(6) 2.80(6) 2.80(13)
χcc (MHz) -4.20(6) -5.39(6) -5.33(13)
Nitrile N
χaa (MHz) -4.11(30) -4.23738(36) -3.309(33)
χbb (MHz) 2.40(13) 2.2886(11) 1.265(13)
χcc (MHz) 1.71(13) 1.9488(11) 2.044(20)
1Hatta, A.; Suzuki, M.; Kozima, K. Bull. Chem. Soc. Jap. 1973, 46, 2321-3.
2Wohlfart, K.; Schnell, M.; Grabow, J. U.; Küpper, J. Journal of Molecular Spectroscopy 2008, 247, 119-121.
3Li, Y. S.; Harmony, M. D. The Journal of Chemical Physics 1969, 50, 3674-3677.
119°6°
Structures
DMABN
DMA113° 22°