IDENTIFICATION AND CHARACTERIZATION OF 1,2-BN CYCLOHEXENE USING MICROWAVE SPECTROSCOPY STEPHEN G. KUKOLICH, MING SUN, ADAM M. DALY University of Arizona JACOB S. A. ISHIBASHI, SHIH YUAN LIU Boston College . ISMS – 16 – WK01

B-N substitution in benzene and cyclohexane AZABORINE - AROMATIC S. Y. Liu – 2009 > OSU - 2010 PLANAR MOLECULE 0 = 0.02 amuÅ2 BOND LENGTH 1.45Å BETWEEN SINGLE AND DOUBLE BOND LENGTH C) eqQ’s CONSISTENT WITH PARTIAL DELOCALIZATION of p ELECTRONS 2 2 2

B-N substitution in benzene and cyclohexane B-N cyclohexane –synthesized by the LIU group  Possible HYDROGEN STORAGE cmpd IN SOLUTION (TOP)  GAS PHASE (BOTTOM)  3 3 3

 Shih-Yuan Liu sent the compound synthesized as 1,2-BN Cyclohexane  (C4H12BN).1 (a)  G09 calculacations were carried out for 1,2-BN Cyclohexene (C4H10BN) [OOPS!] to predict transitions and get the structure. (b) and predict transitions Microwave transitions were found close to the calculated frequencies. 10BN Cyclohexene and11BN Cyclohexene and lines were measured in the frequency range of 5-13 GHz, Shih-Yuan Liu looked at our struture and said “You are have the WRONG COMPOUND! B and N should each have 2 H atoms. 1. Wei Luo, Lev N. Zakharov, and Shih-Yuan Liu, J. Am. Chem. Soc. 2011, 133. 4 4

 EXPERIMENTAL 1,2- BN Cyclohexane synthesized by the Liu lab was placed in a glass cell attached to the pulse valve and sample cell and valve heated to 50 to 90° C to obtain sufficient vapor pressure Flygare-Balle Spectrometer – Homodyne Detection Spectra for 1,2-10BN Cyclohexene (63 lines) and 1,2-11BN Cyclohexene (83 lines) measured in 5.5-12.5 GHz range 1 atm neon gas stream Accurate values for 14N, 11B, and 10B eQq ( ij ) parameters obtained and compared with High-level ab initio calculations – G09 Nuclear spin angular momenta for Boron and Nitrogen are (11B: I= 3/2 and 14N: I = 1) They are coupled as F1 = J + I(11B) and F = F1 + I(14N), where F is the total angular momentum.

 The 111 000 transitions for 1,2- 11BN Cyclohexene showing the quadrupole hyperfine structure arising from 11B and 14N interactions.  F1 = J + I(11B) and F = F1 + I(14N)

Calculated A, B. and C and eQq for 1,2-BN cyclohexane (a) DO NOT AGREE with the EXPERIMENTAL VALUES, essentially ruling out that structure for our gas-phase experiments. . Parameter BN-Cyclohexane BN-Cyclohexene   B3LYP(TZ) Experiment MP2(QZ) A 4253.09 4702.058(2) 4701.56 4754.95 B 4054.51 4360.334(1) 4365.76 4404.60 C 2368.44 2494.407(1) 2486.58 2523.18 1.5 χaa (B) 0.905 -2.698(8) -2.980 -2.804 0.25(χbb- χcc)(B) 0.266 -1.357(3) -1.150 -1.469 1.5χaa (N) -1.463 0.553(6) 0. 629 0.404 0.25(χbb- χcc)(N) -0.168 1.157(2) 1.227 1.136 7 7

The assignment of the EXPERIMENTAL SPECTRA to BN-CYCLOHEXENE is even more clearly supported when we compare the QUADRUPOLE COUPLING ( ij ) values. The 11B ij values for Cyclohexene are close to those for Azaborine. Parameter Cyclohexane Cyclohexene Azaborine   MP2 Experiment χaa (B) 0.603 -1.7989(45) -1.71(1) χbb (B) 0.231 -1.8145(53) -1.33(2) χcc (B) -0.834 3.6135(26) 3.03(2) χaa (N) -0.975 0.3687(43) 0.45(1) χbb (N) 0.152 2.1295(29) 0.25(6) χcc (N) 0.824 -2.4981(23) -0.71(6) 8 8

 Results from the microwave measurements show that heating 1,2 BN cyclohexane in a 1 atm neon stream results in the loss of H2 and conversion to 1,2 BN cyclohexene.  Comparison of the calculated rotational constants for the 1,2-BN cyclohexane and 1,2-BN cyclohexene provides confirmation that the observed spectra arise from the BN cyclohexene.  The differences in the calculated quadrupole coupling constants for the BN cyclohexane and observed values are much more larger and provide a definitive assignment of the observed spectra to the 1,2-BN cyclohexene structure.

Acknowledgements: Prof. Shih-Yuan Liu , Jacob Ishibashi – Boston College We thank Spencer J. Carey for help in collecting some of the preliminary data for this compound and Kexin Li for NMR measurements. N$F – We thank the National Science Foundation for Grants CHE-1057796, CHE-0721505 10 10

ISMS – 16 – P1531

Current Research Group (most) Onur Oncer, Zunwu Zhou, David Mills, Aaron Pejlovas Adam Daly, Mandy Olmut, Stacie Munden, Steven Edwards, Kexin Li, Steve Kukolich