1. THE LAST LAP: HIGH-RESOLUTION INFRARED SPECTROSCOPY OF BUTADIENE-2,3-13C2
NORMAN C. CRAIG and MICHAEL C. MOORE, Department of Chemistry, Oberlin College, Oberlin, OH 44074
ROBERT L. SAMS, EMSL, Pacific Northwest National Laboratory, Richland, WA 99352
DONALD C. MCKEAN, School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, U. K.
PETER GRONER, Department of Chemistry, University of Missouri-Kansas City, Kansas City, MO

2. Problem
Is there structural evidence for π-electron delocalization in butadiene?
Are the “double” bonds somewhat longer than the localized double bond in ethylene?
Is the “single” bond somewhat shorter than an sp2–sp2 single bond?

3. Existing Data sp2-sp2 C––C bond 1.330 Å 1.470 Å
Reference Bond Lengths Ethylene C=C bond
sp2-sp2 C––C bond
1.330 Å
1.470 Å
1. K. Kveseth, R. Seip, and D. Kohl. Acta Chem. Scand., Series A , 34, 31.
2. W. Caminati, G. Grassi, and A. Bauder. Chem Phys. Letters , 148, 13.
3. C. Bock, P. George, and M. Trachtman. Theor. Chim. Acta , 64, 293.
4. N. C. Craig, C. M. Oertel, D. C. Oertel, M. J. Tubergen, R. J. Lavrich, and A. M. Chaka. J. Phys. Chem. A , 106, 4230.

4. Synthesis of BDE-2,3-13C2

5. Observed and Calculated Fundamental Frequencies of BDE-2,3-13C2
a DFT B3LYP/ G** with selectively scaled force constants

6. Gas-phase IR spectrum of butadiene-2,3-13C2

9. Ground State and Excited State Rotational Constants for BDE-2,3-13C2
v11=1
A /cm-1
(6)
(6)
B /cm-1
(2)
(9)
C /cm-1
(2)
(1)
DK  106/cm-1
7.265 (1)
2.229 (3)
DJK  107/cm-1
(4)
(4)
DJ  108/cm-1
2.838 (6)
0.287 (4)
dJ  109/cm-1
3.72 (3)
3.59 (2)
dK  107/cm-1
1.33 (8)
0.98 (1)
n0/cm-1
(2)
Dnrms/cm-1 k
No. of lines
1184
1878
Max. Ka' 20 14
Max. J" 70 40

10. Quantum chemical (QC) calculation of spectroscopic alphas,
Method
Quantum chemical (QC) calculation of spectroscopic alphas,