1. OSU – June - 20061 STEPHEN KUKOLICH, Chemistry Dept., University of Arizona, MICHAEL PALMER School of Chemistry, University of Edinburgh, PETER GRONER, Chemistry, University of Missouri-Kansas City, and CHAKREE TANJAROON, Chemistry, University of Alberta, Experimental Rotational Spectra for MnRe(CO) 10 and o-C 6 H 4 † Required Accurate theoretical Calculations for Successful Analysis † Measured at Harvard with Pat Thaddeus and Mike McCarthy

2. OSU – June - 20062  Observing and Measuring the Rotational Transition Frequencies was Difficult  B = 200.3687 MHz ( 187 Re )  eQq( 187 Re) = 370.42(38) MHz  eQq( 55 Mn) = -16.52(5) MHz  Normal Isotopomer transitions were readily observed  13 C Isotopomer lines often obscured by other products of Discharge (Shotgun effect)

3. OSU – June - 20063 MnRe(CO) 10 + > Symmetric top with C 4v symmetry -> Combination of small B-values with two quadrupoles resulted in congested and difficult-to-assign spectra (J=11 → 12 and 12→ 13 ) + > Michael Palmer and Martyn Guest (Edinburgh) calculated the eQq values sufficiently accurately to allow unambiguous assignments of the spectra

4. OSU – June - 20064 Example Spectra for 8, and 10 MHz “pieces” of the spectrum

5. OSU – June - 20065 Pair of measured transitions 2000 Shots

6. OSU – June - 20066  C 4v symmetry  Only K=4n transitions observed  Staggered or Eclipsed? † † F. A. Cotton, Austin 2004 (E) (S) xx

7. OSU – June - 20067

8. 8 The structure of o – benzyne and vibrational averaging effects. Spectra Measured on HARVARD FTMWS 1 Discharge 0.5% BENZENE in NEON Normal Isotopomer - 27 b-dipole transitions 13 C 6 - 12 b-dipole transitions D1 - 26 b-dipole transitions D2 - 23 b-dipole transitions 13 C 1 (1) - 10 b-dipole transitions 13 C 1 (3) - 9 b-dipole transitions 13 C 1 (5) - 10 b-dipole transitions 1. S. G. Kukolich, M. C. McCarthy and P. Thaddeus, J. Phys. Chem. 108, 2645-2651, (2004) DIFFICULT To MEASURE

9. OSU – June - 20069 Search for 13 C lines… in a sea of lines from other radicals and molecules produced in the DISCHARGE. JUNK WRONG MOLECULE GOOD ONE kHz

10. OSU – June - 200610 Least-squares structure fit  The inertial defect for the normal isotopomer of o-benzyne is  = I CC – I AA – I BB = 0.06935(1) amu Å 2, consistent with a PLANAR STRUCTURE.  This value is sufficiently large that when trying to fit the measured A, B, and C rotational constants with a planar structure, some of the deviations will be as large as 1 MHz.  STANDARD DEVIATION FOR FIT = 1.05 MHz  Experimental errors are < 2 kHz! EXPTCALC.DEV. NORMAL A 6989.729 6989.915 -0.186 B5706.8065706.891-0.085 C3140.3713141.789-1.418 13C1 A6859.7306859.886-0.155 B5679.5165679.3690.147 C3105.740 3107.029-1.289

11. OSU – June - 200611 Least-squares fit to determine the structure  Most of the same vibrational averaging effects which contribute to the differences between the r 0 and r e coordinates, will also contribute to this inertial defect.  Problem 1. We are trying to fit a PLANAR, (r e ) structure to EXPERIMENTAL A, B, and C which have non-zero inertial defect,  (characteristic of the r 0 coordinates )  Problem 2. The r 0 coordinates are different for each of the measured isotopomers  SOLUTION: Find the  k, vibration-rotation constants, so we fit the r e structure,  same for all isotopomers

12. OSU – June - 200612 VIBRATIONAL AVERAGING EFFECTS – RELATED TO VIBRATION-ROTATION INTERACTION CONSTANTS  k Values for these  k were calculated by Peter Groner 1, University of Missouri

13. OSU – June - 200613 Final Structure of o-benzyne  r(C 1 -C 2 ) for HCCH =1.203 Å r(C 1 -C 2 ) for H 2 CCH 2 =1.332 Å Now the fit is MUCH improved (  < 30 kHz)  r(C 2 -C 3 ) for benzene =1.3914 Å P. Groner and S. G. Kukolich, J. Mol. Struct. 780-781, 178 (2006)  r(C 2 -C 3 ), NMR value → 1.24(2) Å Grant, Michl, et al.

14. OSU – June - 200614 The r e structure of o-benzyne (Distances r in Å) Structural parameter rere MP2/ 6-31G(d) r s / Kraitch- man B3LYP/ 631G(d,p) BPW9 1/ cc- pVDZ Ref.This work [a][b][c] r(C 1 -C 2 )1.255(3)1.2681.255(8)1.2511.266 r(C 2 -C 3 )1.383(2)1.3891.40(2)1.3851.391 r(C 3 -C 4 )1.403(2)1.4051.39(2)1.4121.423 r(C 4 -C 5 )1.405(3)1.4101.404(14)1.4071.412 r(C 3 -H 1 )1.080(1)1.0861.08(2)1.0851.098 r(C 4 -H 2 )1.082(1)1.0881.084(9)1.0871.100 Benzene r(C-C) b 1.3914(1)1.395 r(C-H) b 1.0825(3)1.087 [ a]S. G. Kukolich, M. C. McCarthy, P. Thaddeus, J. Phys. Chem A 108 (2004) 2645-2651. [b]S. G. Kukolich, C. Tanjaroon, M. C. McCarthy, P. Thaddeus, J. Chem. Phys. 119 (2003) 4353-4359. [c]C. J. Cramer, Nash, J. J. and R. R. Squires, Chem. Phys. Lett. 277 (1997) 311-320.

15. OSU – June - 200615 Acknowledgements N$F - This material is based upon work supported by the National Science Foundation under Grant No. CHE-0304969. This support from the National Science Foundation is gratefully acknowledged Willis Flygare and Terry Balle Harvard: Pat Thaddeus, Mike McCarthy Arizona: Kristen Keck Edingburgh: Martyn Guest, Phillip Camp Department of Chemistry, University of Arizona.

16. OSU – June - 200616

17. OSU – June - 200617 Other isomers of benzyne The structural isomers of didehydrobenzene – ortho-benzyne, meta-benzyne and para-benzyne. Calculations show  H f  (o-benzyne) >  H f  (m- benzyne)>  H f  (p-benzyne)

18. OSU – June - 200618 O - BENZYNE  Brown, Godfrey, Rodler, Robertson (1st microwave, no structure)  Pyrolyzed: pthalic anhydride, or ninhydrin, or benzocyclobutene-R(1986, 2003)  Lineberger, Squires, et al. (1998)- electron afinities, singlet triplet splittings & vibrational frequencies PRESENT WORK (2002…)  Discharge 0.5% BENZENE in NEON  HARVARD SPECTROMETER (Sabbatical)