Rotational Analysis of Bands in the High-Resolution Infrared Spectra of trans,trans-

and cis,cis-1,4-Butadiene-2-d1

Norman C. Craig, Deacon J. Nemchick, Clay C. Easterday, Ethan C. Glor, and Drew F. K. Williamson,

Department of Chemistry and Biochemistry, Oberlin College, Oberlin, OH 44074, USA Norm.Craig@oberlin.edu

Thomas A. Blake and Robert L. Sams

Environmental Moleculat Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352

Overall Goal

Determine semi-experimental equilibrium structures for the isomers of 1,4-difluorobutadiene (DFBD).

Evaluate the influence of fluorine substitution on the CC bond lengths and bond angles in butadiene. (Strong influence of fluorine on C3 and C4 rings.)

Steps in Determining Semi-Experimental Equilibrium Structures

• Obtain ground state rotational constants from high-resolution IR or MW spectra.

• Do so for a full series of isotopomers.• Use quantum chemistry (triple zeta level) to compute

vibration-rotation constants (alphas). • Find equilibrium rotational constants

• Obtain an re structure from a global fit of all equilibrium rotational constants.

€

Be, k ≈ B0, k +1/ 2 αk,ιi =1

n

∑

SynthesisIsotopomers of DFBD are made by modification of an assembly strategy.1

1H.-G.Viehe and E. Franchimont Chem. Ber. 1964, 97, 602-609.

IR spectrum (0.1 cm-1 resol.) cis,cis-2-d1 species

A-type C-type

C-type Band (0.0013 cm-1 resol.) of cis,cis-2-d1 Species

A-type Band (0.0013 cm-1 resol.) of cis,cis-2-d1

Species

Loomis-Wood Display for A-Type Band of cis-2-d1 Species

Ka 6lo yellow, 6hi magenta, 7 red, 8 green, 9 blue,10 brown, 11 pink, 12 orange, 13 purple

Rotational Constants for cis,cis-1,4-Difluorobutadiene-2-d1 ground state 13(a') – A-type 20(a") – C-type A 0.4195784(5) 0.420147(1) 0.418391(6) B 0.0536490(5) 0.05366108(6) 0.053651(6) C 0.0475823(6) 0.04753482(7) 0.047602(6)

J ×108 0.10848a 0.10848a 0.10848a K ×107 0.22351a 0.22351a 0.22351a K ×106 0.6442(3) 0.626(6) 0.075(19) J K ×107 -0.806(1) -1.050(2) -0.63(2) J ×108 0.774(3) 0.7975(4) 0.764(6) -0.96738 -0.96712 -0.96737 0 865.78495(4) 775.4 . .s d 0.00039 0.00045 0.00037 b -0.1145 0.3645 -0.3603

No. lines 1357c 1328 427 Ka' 0–34 0–13 10–15 Jmax 88 90 80 a Calculated wit h 3B L /YP cc-pVTZ model. b Inertial defect, = Ic – Ia – Ib. c 426 GSCDsfro mth eA-type band.

IR spectrum (0.1 cm-1 resol.) trans,trans-2-d1 species

C-type

C-type Band (0.0013 cm-1 resol.) of trans,trans-2-d1 Species

C-type Band (0.0013 cm-1 resol.) of trans,trans-2-d1 Species

Rotational Constants for trans,trans-1,4-Difluorobutadiene-2-d1 ground state 18(a") – C-type 21(a") – C-type A 0.939012(1) 0.93539(4) 0.937033(2) B 0.0389226(4) 0.03902(1) 0.03892105(4) C 0.0373779(3) 0.03729(1) 0.03738859(3)

J ×1010 0.63702a 0.63702a 0.63702a K ×108 0.73286a 0.73286a 0.73286a K ×106 2.766(2) -3.2(5) 3.36(3) J K ×107 -0.279(3) 1.5(2) -0.321(3) J ×108 0.133(3) 0.19(1) 0.1351(3) -0.99657 -0.99614 -0.99660 0 914.3 709.01914(4) . .s d 0.00037 0.0020 0.00040 b -0.0539 2.0199 -0.2212

No. lines 1158c 380 974 Ka' 0–21 4–8 0–9 Jmax 88 50 96 a Calculated wit h 3B L /YP cc-pVTGZ model. b Inertial defec ,t = Ic – Ia –

Ib. c 153 GSCDsfro mth eA-type band.

Conclusions

Analysis of the rotational structure in the high-resolution (0.0013 cm-1) infrared spectra of the cis,cis and trans,trans isomers of 1,4-difluorobutadiene has yielded ground state rotational constants.

Prior work gave ground state rotational constants for the normal species.1

The polar cis,trans isomer was investigated by MW spectroscopy.2

1. N. C. Craig, M. C. Moore, C. F. Neese, D. C. Oertel, L. Pedraza, T. Masiello J. Mol.

Spectrosc. 2009, 254, 39-46.

2. N. C. Craig, P. Groner, D. C. McKean, M. J. Tubergen Int. J. Quant. Chem. 2003, 95, 837-

852.

Support

Dreyfus Foundation

National Science Foundation

Oberlin College

Washington State University