1. Chirality of and gear motion in isopropyl methyl sulfide: Fourier transform microwave study Yoshiyuki Kawashima, Keisuke Sakieda, and Eizi Hirota* Kanagawa Institute of Technology The Graduate University for Advanced Studies* 6/24/2010 RH03

2. Chiral molecule eg. propylene oxide (PO) Second chiral molecule eg. isopropanol (IPOH) （ R ） and (S) of PO gauche and gauche’ of IPOH

3. Gear Motion Pitzer and his collaborators devised to explain the thermodynamical data of some organic molecules. J.E.Kilpatrick and K.S.Pitzer, J. Res. Natl. Bur. Stand., 37 (1946) 16 cis-2-butene: CH 3 CH=CHCH 3 Kondo et al. concluded the CH 3 conformation which was not compatible with the gear motion for cis-2-butene by a MW spectroscopy. S. Kondo, Y. Sakurai, E. Hirota and Y. Morino, J. Mol. Spectrosc., 34 (1970) 231 (HCCH) 2 IR and MW spectra of interconversion tunneling in acetylene dimer Y. Ohshima, Y. Matsumoto, M. Takami, and K. Kuchitsu, Chem. Phys. Lett., 27 (1988) 1 G. T. Fraser, R. D. Suenram, F. J. Lovas, A. S. Pine, J. T. Hougen, W. J. Lafferty, and J. S. Muenter, J. Chem. Phys., 89 (1988) 6028.

4. (CH 3 ) 2 CHOCH 3, IPME Gauche form was found by Nakagawa et.al., however, trans form has not been observed. V 3 = 603.3 cm -1 J. Mol. Struct. 112 (1984) 201 Our aim (CH 3 ) 2 CHSCH 3, IPMS

5. Potential function of IPMS ab initio calculation MP2/6-311G(d,p) trans gauche cm -1 HC-SC deg μ a = 0.3 D μ b = 1.5 D μ c = 1.0 D μ a = 1.6 D μ b = 0.0 D μ c = 0.9 D V 3 (S-CH 3 ) = 500~550 cm -1 V 3 (isop-CH 3 ) ≈1300 cm -1

6. Instrument: Fourier transform microwave spectrometer Sample : 0.5% IPMS diluted with Ar Backing pressure : 1~2 atm Shots : 20 Frequency region : 5~23 GHz Step : 0.25 MHz MW sample Supersonic molecular beam injection Experimental Vacuum chamber Mirror (mobile) Diffusion pump Rotary pump Mirror (fixed) Molecular beam injection nozzle

7. 100001500020000 Frequency/MHz Spectrum of IPMS 8500-10500 MHz expand 85009000100009500 10500 4 22 -4 13 Gauche form b-type transition Q-branch 5 23 -5 14 3 21 -3 12 6 24 -6 15 2 20 -2 11 Frequency/MHz

8. Spectra of IPMS 10000 1500020000 Frequency/MHz Gauche form Trans form 100001500020000 Frequency/MHz 5000 a-type J=2←1 a-type J=3←2 a-type J=4←3

9. Observed Splittings of gauche and trans of IPMS 250 8980.8 8981.6 150 15631.515632.3 14371.4 14372.2 0 0 0 250 Frequency/MHz a-type b-type c-type 3 12 -2 11 2 11 -1 01 5 23 -5 14 Frequency/MHz Splittings of internal rotation of CH 3 group Gauche form 16344.316345.1 0 15 0 50 18090.118090.9 2 21 -1 11 2 11 -1 01 Frequency/MHz Trans form 3 12 -2 11 a-type c-type A E E E E E A A A A ？

10. Molecular parameters of gauche and trans of IPMS Experimental gauche trans A /MHz 6039.36375(6)5105.38888(11) B /MHz 2777.50750(4)2774.42333(9) C /MHz 2128.157503(4)2578.42201(8) N(a-type) 38 32 N(b-type) 148 - N(c-type) 100 131 V 3 /cm -1 σ  kHz 601.64(7) 2.0 559.00(11) 3.2 ab initio Calculation MP2/6-311++g(d,p)B3LYP/6-311++g(d,p) gauche trans gauche trans A /MHz 60495100 59885072 B /MHz 28042788 2697 C /MHz 21362599 20842511 μ a /D -0.27 1.58 0.27 1.47 μ b /D 1.53 0 1.37 0 μ c /D 0.97 0.94 0.99 -0.89 V 3 /cm -1 518 566 507 521 ΔE /cm -1 0 192 0 229

11. Selection rule: A’ ↔ A’’ s ↔ s and a ↔ a ； a-type and c-type transitions s ↔ a; b-type transition g’g gauche

12. Analysis for gauche of IPMS F: the first-order internal-rotation term Δ: the tunneling splitting δ: the K-type doubling iQ: the interaction term between the s and a states: -iQK a s state a state +K -K

13. E state s 3 22 s 3 21 a 3 21 a 3 22 s 3,3(-) a 3,3(-) a 3,3(+) s 3,3(+) s 3 22 s 3 21 a 3 21 a 3 22 s 3 31 a 3 31 a 3 30 s 3 30 A state Gauche of IPMS A state E state 17555.817556.6 / MHz 17563.2 17564.0 / MHz 3 31 -3 21 3 30 -3 21 / MHz 17554.017554.8 a-a allowed s-s allowed a-a forbidden s-s forbidden / MHz 17564.5 17565.3 s-a forbidden a-s forbidden s-a allowed a-s allowed a-a s-s s-a a-s

14. Analysis for gauche of IPMS F: -3.66 MHz δ: 7.471 MHz for J = 3 and 51.74 MHz for J = 4 A stateE state Δ: around 0.001 MHz 0.001~0.002 MHz iQ: 6.47 MHz 9.05 MHz The difference in iQ between the A and E states is probably due to the CH 3 internal rotation, which, when being the E state, contributes to the Coriolis interaction term –iQKa.

15. Observed Splittings of gauche and trans of IPMS 250 8980.8 8981.6 150 15631.515632.3 14371.4 14372.2 0 0 0 250 Frequency/MHz a-type b-type c-type 3 12 -2 11 2 11 -1 01 5 23 -5 14 Frequency/MHz Gauche form 16344.316345.1 0 15 0 50 18090.118090.9 2 21 -1 11 2 11 -1 01 Frequency/MHz Trans form 3 12 -2 11 a-type c-type A E E E E E A A A A ？

16. E state 3 22 3 21 3,3(-) 3,3(+) 3 22 3 21 3 31 3 30 A state Trans of IPMS A state Allowed transition of E state Forbidden transition of E state 12092.7 12093.5 / MHz 12090.412091.2 / MHz 12095.312096.1 / MHz 3 31 - 3 21 Sat I Sat II Sat

17. 36 cm -1 for trans 68 cm -1 for gauche C(isop) - S torsion The lowest vibrational modes of trans and gauche of IPMS We need to treat this rotational isomer as a system which consists of one methyl of S-CH 3 and two methyl groups (CH 3 ) 2 CH and internally rotating about the C(isop)-S bond. This system belongs to a group G 54, which Ohashi and Hougen discussed in some detail. J. Mol. Spectrosc. 211 (2002) 119. The S-CH 3 internal rotation, when coupled in gear-like fashion with those of the two CH 3 in (CH 3 ) 2 CH group, will yield three substrates each for the A and E states: A 1, A 1+, A 1- and E 1, E 1+, E 1-, and we suspect that A 1+ and A 1- are merged into the A satellite and E 1+ and E 1- correspond to sat I and II, respectively. The above-mentioned ab initio calculation reveals the C(isop)-S tortional frequency to be 36 cm -1 around the trans, compared with 68 cm -1 at the gauche conformation.

18. angle of the C(isop) – S torsion Potential functions for the C(isop) – S torsion in gauche and trans of IPMS

19. C(isop) - S torsion CH 3 - S internal rotationisop C - S - CH 3 bending isop anti-gear CH 3 internal rotation isop gear CH 3 internal rotation 36 cm -1 for trans 68 cm -1 for gauche 175 cm -1 164 cm -1 240 cm -1 238 cm -1 246 cm -1 217 cm -1 267 cm -1 270 cm -1 Vibrational modes of trans of IPMS

20. Summary 1. The existence of two rotational isomers gauche and trans was established for IPMS. 2. Some gauche spectra were found split, which were explained by the tunneling between the two equivalent forms and were thus of great significance for the racemization process in the chiral gauche. 3. Trans showed unique satellite spectra, which were ascribed to the excited state of the C(isop) – S torsion perturbed by the “gear” type motion between the CH 3 groups in the isopropyl radical and the CH 3 directly bonded to the S atom. Future works 1.Analyze the satellite spectra of the trans of IPMS 2. Reinvestigate the spectrum of IPME. Acknowledgements We thank Dr. Yoshihiro Osamura for his advise in performing ab initio calculation.