RANIL M. GURUSINGHE, MICHAEL TUBERGEN Department of Chemistry and Biochemistry, Kent State University, Kent, OH. RANIL M. GURUSINGHE, MICHAEL TUBERGEN.

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RANIL M. GURUSINGHE, MICHAEL TUBERGEN Department of Chemistry and Biochemistry, Kent State University, Kent, OH. RANIL M. GURUSINGHE, MICHAEL TUBERGEN Department of Chemistry and Biochemistry, Kent State University, Kent, OH.

Indole Chromophore of the amino acid tryptophan; responsible for the bulk of UV absorption in proteins Motivation : Methylated Indoles Internal rotor problem with quadrupole coupling As a learning experience Methyl substitution and torsional barrier Position of substitution/ symmetry of electronic distribution/ barrier to methyl internal rotation

Fitting Strategy 1.Rotational constants estimated Geometry optimization at MP2/ G(d,p) 2.Barrier height estimated Relaxed potential scan at wB97XD/ G(d,p) 3.A component line centers were fitted RRFIT/ZFAP 4.Quadrupole hyperfine components were fitted QUAD2 5.A and E components fitted simultaneously XIAM

MP2/ G(d,p) A (MHz) B (MHz) C (MHz) μ a = > μ b = > μ c = D A (MHz) B (MHz) C (MHz) μ a = > μ b = > μ c = D A (MHz) B (MHz) C (MHz) μ b = > μ a = > μ c = D A (MHz) B (MHz) C (MHz) μ a = > μ b = > μ c = D 1-methylindole 3-methylindole 2-methylindole 5-methylindole

Relaxed Potential Surface Scan 1-MI2-MI3-MI5-MI Barrier / cm Barrier estimation at wB97XD/ G(d,p)

Mini Cavity FTMW Spectrometer Range : 10.5 – 22 GHz Resolution : 2.4 kHz Temperature : 90 – C Carrier Gas : Ar Backing pressure : 1.5 atm

1-methylindole (E) (A) F 5-4 F 6-5 F 4-3 F 5-4 F 6-5 F 4-3

1-methylindole ParameterXIAMMP2/ G(d,p) A (MHz) (17) B (MHz) (5) C (MHz) (5) ΔJ (kHz)0.056 (6) ΔJK (kHz) (23) ΔK (kHz) (12) δJ (kHz) (22) δK (kHz)0.213 (5) χ aa (MHz)1.729 (12) χ bb - χ cc (MHz)5.455 (14) N152 Δν rms (kHz)9.81 ParameterXIAM V 3 (cm -1 )279.8 (4) F 0 (GHz) (24) I α (uA 2 )3.186 (5) ε (rad) (15) < (i,a) (4) < (i,b) (4) < (i,c) (7)

2-methylindole ParameterXIAMMP2/ G(d,p) A (MHz) (4) B (MHz) (4) C (MHz) (2) ΔJ (kHz) (15) ΔJK (kHz)0.070 (25) ΔK (kHz)2.2 (6) δJ (kHz) (11) δK (kHz)0.399 [fixed] χ aa (MHz)1.74 (4) χ bb - χ cc (MHz)5.25 (3) N154 Δν rms (kHz)6.88 ParameterXIAM V 3 (cm -1 )381.3 (13) F 0 (GHz)161.1 (6) I α (uA 2 )3.137 (11) ε (rad)0.00 [fixed] < (i,a) [fixed] < (i,b)90.0(<0) < (i,c)89.92(<0)

3-methylindole ParameterXIAMMP2/ G(d,p) A (MHz) (5) B (MHz) (1) C (MHz) (1) ΔJ (kHz) (17) ΔJK (kHz) (6) ΔK (kHz)0.26 (3) δJ (kHz) (6) δK (kHz)0.059 (11) χ aa (MHz)1.783 (4) χ bb - χ cc (MHz)5.209 (4) N154 Δν rms (kHz)2.33 ParameterXIAM V 3 (cm -1 )433 (1) F 0 (GHz)161.1 (4) I α (uA 2 )3.136 (8) ε (rad)0.01 (3) < (i,a) (6) < (i,b) (1) < (i,c) (14)

5-methylindole ParameterXIAMMP2/ G(d,p) A (MHz) (6) B (MHz) (5) C (MHz) (4) ΔJ (kHz) (25) ΔJK (kHz)-0.01 (3) ΔK (kHz)5.8 (11) δJ (kHz)0.014 (11) δK (kHz)0.29 (8) χ aa (MHz)1.73 (3) χ bb - χ cc (MHz)5.058 (19) N152 Δν rms (kHz)7.75 ParameterXIAM V 3 (cm -1 ) (4) F 0 (GHz) (5) I α (uA 2 ) (10) ε (rad) (9) < (i,a) (6) < (i,b) (6) < (i,c) (15)

Discussion Torsional potentials are sensitive indicators of the symmetry of the electron distribution in the molecular frame at the site to which methyl rotor is attached 1-MI2-MI3-MI5-MI XIAM (cm -1 )279.8 (4)382 (1)433 (1) (4) MP2/ G(d,p) (cm -1 ) Electronic Spec 1,2,3,4 (cm -1 ) χ aa (MHz)1.729 (12)1.74 (4)1.783 (4)1.73 (3) χ bb (MHz) - χ cc (MHz)5.455 (14)5.25 (3)5.209 (4)5.058 (19) 1.T. M. Korter and D. W. Pratt, J. Phys. Chem. B. 105, 4010 (2001) 2.K. Remmers, E. Jalviste, I. Mistrik, G. Berden, W. L. Meerts, J. Chem. Phys. 108, 8436 (1998) 3.D. M. Sammeth, S. S. Siewert, P. R. Callis, L. H. Spangler, J. Phys. Chem. 96, 5771 (1992) 4.G. A. Bickel, G. W. Leach, D. R. Deemer, J. W. Hager, S. C. Wallace, J. Chem. Phys. 88, 1 (1987)

Acknowledgement Dr. Sean and Dr. Rebecca Peebles Dr. Heinrich Mäder Dr. Arun Manna Ohio SuperComputer center Kent State University

Steric Hindrance Shortest distance (Methyl Hydrogen and Indole ring hydrogen) Å 1MI MI MI MI2.382

CompoundExp Barrier / cm-1 1Methyl(difluoro)silyl chloride468 (3) 2Methylisobutyl ketone250.3 (19) 3Acetone264.7 (8) 4Methyl vinyl ketone424 (7) 5Methyl ethyl ketone183 (5) 6Most Acetic acid estersAround 100 7Trifluoroacetylacetone379 (CH3) 30.8 (CF3) 8o-toluidine m-toluidine o-Tolunitrile m-Tolunitrile O-flurotoluene m-flurotoluene 227