Microwave Spectra, Structure, and the Aromatic Character of 1

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Microwave Spectra, Structure, and the Aromatic Character of 1-Chloroborepin Aaron M Pejlovas, Zunwu Zhou, Arthur James Ashe, and Stephen George Kukolich J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.7b10571 • Publication Date (Web): 25 Jan 2018 Downloaded from http://pubs.acs.org on January 26, 2018

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The Journal of Physical Chemistry

Microwave Spectra, Structure, and the Aromatic Character of 1-Chloroborepin

Aaron M. Pejlovasa, Zunwu Zhoua, Arthur J. Ashe IIIb, and Stephen G. Kukolicha a) Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721 b) Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055

Abstract High resolution microwave spectra for the somewhat unstable compound, 1chloroborepin were measured in the 5-10 GHz range using a pulsed beam Fourier transform microwave spectrometer. Transitions were assigned and measured for three isotopologues, which include the most abundant isotopologue, 11B35Cl, and the less abundant 10B35Cl and 11B37Cl isotopologues. The molecular parameters (in MHz) determined for the 11B35Cl isotopologue are A = 3490.905(35), B = 1159.38520(79), C = 870.59492(56), 1.5χaa (11B) = -0.220(22), 0.25(χbb – χcc) (11B) = -1.5300(99), 1.5χaa (35Cl) = -54.572(33), and 0.25(χbb – χcc) (35Cl) = 4.7740(79). The inertial defect is calculated to be ∆ = -0.174 amu Å2 from the experimental rotational constants, indicating a planar structure with some out of plane vibrational motion. An extended Townes-Dailey analysis was performed on the 11B and 35Cl nuclei to determine the electron occupations in the valence hybridized orbitals using the experimental quadrupole coupling strengths. From the analysis it was determined that Cl is sharing some electron density with the empty p-orbital on B. The B-Cl bond length determined from the data is 1.798(1) Å and the B-C bond lengths are 1.533(10) Å. The structural

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parameters and electronic structure properties of 1-chloroborepin are consistent with an aromatic boron-containing molecule.

1) Introduction Boron is an interesting electron deficient element. It is a trivalent atom with an empty p-orbital, making it an attractive π-electron acceptor for chemists to use to manipulate the properties of organic molecules. Boron chemistry has interested chemists for years because the empty valence p-orbital allows for inducing interesting optical and electronic properties within these molecules.1,2 As an example, the B-N bond is isoelectronic with the C=C bond and BN-substituted heterocycle aromatic molecules have been shown to have interesting applications in biology, hydrogen storage, and organic electronic devices.3,4 When boron is substituted into conjugated heterocycles, the boron containing species may exhibit additional properties to extend their use to optical materials,5,6,7 chemical sensors,8,9,10 tunable π-conjugated materials,11 and electronic devices such as organic LEDs.12,13,14 Boron is isoelectronic with the carbocation which is an intermediate in many types of organic reactions,15,16,17,18 so understanding the chemistry and aromatic character of boron containing molecules is critical to advancing boron chemistry. Borepin is a neutral molecule that is isoelectronic with the aromatic tropylium cation and because of this, borepin is thought to have some aromatic character. It was postulated back in 1960 that borepin might be a Huckel 6π-aromatic molecule,19 and later spectroscopic, crystallographic, and computational studies have confirmed that it only has a fraction of the aromatic character seen in the all-carbon analogues.20 Ashe


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and coworkers have been investigating these borepin materials for years and in 1992 the synthesis of 1-chloroborepin was successful. 1-chloroborepin could then be converted to a number of other 1-substituted borepins.21 The aromaticity of 1chloroborepin was then investigated by obtaining a X-ray crystal structure of the compound and also a tricarbonyl(1-chloroborepin)molybdenum complex, which formed more stable crystals.22 Based on the molecular structure, they concluded 1chloroborepin resembles that of an aromatic molecule due to the C-C bond distances in the ring resembling that of the aromatic analogues. The aromatic character of molecules can also be investigated by measuring the high-resolution microwave spectra of the molecule to obtain the electric quadrupole coupling strengths of the quadrupolar nuclei – 10B, 11B, 35Cl, and 37Cl in the case of 1chloroborepin. The microwave spectrum was previously measured at high frequency and low resolution, so these quadrupole parameters were unable to be determined.23 From this previous microwave study the molecule was determined to be planar as indicated by its inertial defect. The quadrupole coupling strengths that are obtained from high-resolution spectra are then related to the electron populations in each of the hybridized orbitals, using an extended Townes-Dailey analysis that has been described in detail by Stewart Novick.24 This analysis has been performed on the BNheteroaromatic molecules 4a,8a-azaboranaphthalene25 and 1,2-dihydro-1,2azaborine.26 From the analysis these molecules were found to have aromatic character similar to other nitrogen containing aromatic molecules such as pyrrole. Relating the results obtained from the extended Townes-Dailey analysis to that of natural bond orbital calculations will provide additional insight into the aromatic character for 1-



chloroborepin, as well as provide the additional electronic structure information gained from the hyperfine structure in the spectra.

2) Synthesis and Microwave Measurements We have previously reported on the synthesis of 1-chloro-1H-borepin.27 The 1chloroborepin was prepared by the reaction of 1,1-dibutyl-1H-stannepin with boron trichloride in pentane under nitrogen at -78 °C, shown in Scheme 1. After the reaction was complete, the pentane was removed by distillation at atmospheric pressure leaving a residue which was subject to pot-to-pot distillation at a pressure of 0.1 Torr with an external temperature under 90 °C. The 1-chloroborepin was collected in a receiver cooled to -78 °C as an ice-like solid which is sensitive to water and oxygen. The initial purity was estimated to be >90% on the basis of H- and B-NMR spectra. Microwave measurements on a synthesized sample of 1-chloroborepin from the Ashe lab were made in the 5-10 GHz range using a Flygare-Balle type pulsed-beam Fourier transform microwave spectrometer at the University of Arizona.28,29 Prior to the beam pulse of the molecular sample, the pressure inside the vacuum enclosure was maintained at 10-6 to 10-7 Torr. Ne was used as the carrier gas and before passing over the molecular sample, the Ne was passed through a suppelco OMI-1 purifier tube that was purchased from Sigma Aldrich. The backing pressure of the Ne was maintained at slightly less than 1 atm during the length of the measurements. The vapor pressure of the sample was sufficient that measurements were made with 5/1 signal to noise in a single pulsed beam cycle at room temperature. However, the sample is extremely sensitive to decomposition at room temperature. Decomposition also occurs at even


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lower temperatures of -20 °C. Therefore, it was necessary to take great care in the handling and storage of 1-chloroborepin in order to measure a sufficient number of transitions with the sample provided. The sample decomposed before additional isotopologue transitions could be measured. The measured transitions for the 11B35Cl, 10 35

B Cl, and 11B37Cl isotopologues are listed in Tables 1-3 respectively. The fit rotational

constants and quadrupole coupling strengths for the B and Cl nuclei are listed in Table 4.

3) Calculations Ab initio and DFT computations were performed on 1-chloroborepin with the Gaussian 09 suite30 using B3LYP, MP2, and CCSD methods. These computations were performed on the high performance computing system at the University of Arizona. The computational and experimental rotational constants of the 11B35Cl isotopologue are listed in Table 5 for comparison. In order to predict the rotational transitions in the 5-10 GHz range, the rotational constants from the previous microwave study on 1-chloroborepin were used in Pickett’s SPCAT program.31 The constants obtained in the previous study proved to be relatively accurate in predicting the most abundant isotopologue transitions. The calculated dipole moment from the MP2 computation was 3.6 D along the a-principal axis, leading to the measurements of strong a-type rotational transitions. Following the correct assignments of the new measured rotational transitions for the most abundant isotopologue, the fitting analysis was performed using Pickett’s SPFIT program and a new set of experimental rotational constants and the quadrupole coupling strengths for the B and



Cl nuclei were determined. Only the newly measured transitions were used in the fitting analysis and this was due to the previously measured transitions having large J-values and were measured at low resolution so the hyperfine splittings were not resolved and the quadrupole coupling strengths were not determined. Furthermore, the hyperfine splitting caused by the electric quadrupole interactions diminish at large J transitions, so these coupling strengths could only be determined with high-resolution, lower frequency spectra measured in this study. The 10B35Cl and 11B37Cl transitions were predicted by first finding a set of ratios, to be used as scale factors, using the experimentally determined rotational constants of the 11B35Cl isotopologue and the B3LYP/aug-cc-pVQZ optimized values for the molecule. These ratios were multiplied by the calculated rotational constants for each of the other isotopologues. These calculated rotational constants of the less abundant isotopologues were determined using the B3LYP optimized structure, and changing the mass of one of the substituted atoms within the molecule, and recalculating the moments of inertia and rotational constants of the substituted molecule using Kisiels PMIFST program.32 These calculated constants of the other isotopologues were then multiplied by the ratios described above, and these scaled constants were then used in Pickett’s SPCAT program to predict the transition frequencies. These calculated scaled constants were very close to the experimentally determined values.

4) Rotational Constants and Molecular Structure The rotational constants obtained in the microwave fit are listed with the optimized parameters from the calculations in Table 5. The MP2 computation yielded


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rotational constants closest to the experimentally determined values. The optimized structure obtained from the MP2 calculation also agreed the best with values obtained experimentally, as can be seen with the values of the second moments, also listed in Table 5. The values of the second moments indicate the extension of the molecule along each of the principal axes,33 so by comparing these values it can be seen that the optimized MP2 structure provided a structure which more closely resembles the experimental structure of the molecule. What each calculation fails to determine is the extent of out of plane vibrations within the molecule, indicated by the experimental inertial defect in the last row of Table 5. The slight non-zero negative value obtained from the experimentally determined rotational constants indicate there are some slight out of plane vibrations associated with the molecule. 34 Using the rotational constants determined for three isotopologues (11B35Cl, 10 35

B Cl, and 11B37Cl), a least squares structure fit was performed to obtain key structural

parameters, which include the B-Cl and B-C bond lengths. During the structure fit, the bond lengths of the ring in the molecule were held fixed to the parameters obtained from the X-ray crystal structure. The C-H bond lengths were all held fixed to the optimized (B3LYP/aug-cc-pVQZ) values, 1.086 Å. This was done because even though the optimized structural parameters are from an equilibrium structure, we believe the C-H bond lengths do not change much in the ground state and so fixing these bond lengths is a reasonable approximation to use in the least squares structure fitting routine. Finally, the entire molecule was fixed to a planar structure, since the X-ray crystal structure and the inertial defect calculated from experimental parameters (-0.174 amu Å2) indicate a fairly planar molecule.



During the fitting routine, all atoms were held fixed, except the Cl atom and the C-H groups adjacent to the B atom. The C-H groups (C-H = 1.086 Å) adjacent to the B nucleus were varied by the same variable parameter along the b principal axis as depicted in Figure 1. The a-coordinate for the Cl nucleus was allowed to vary. Using the 9 experimental rotational constants, there were a total of 2 varied parameters that were used to fit the molecular structure around the B atom with the determined rotational constants from the measured transitions. The best fit structure is shown in Figure 1, along with all of the structural parameters of this structure. The standard deviation in the calculated rotational constants of the best fit structure compared with all of the experimentally determined values is 0.56 MHz. The calculated rotational constants of the best fit structure are listed in Table 6 with the experimental values as a comparison. This standard deviation is very small compared with the magnitudes of the rotational constants of the molecule and so the newly obtained bond lengths help to accurately refine the gas phase molecular structure of 1-chloroborepin. The microwave B-Cl bond length is 1.798(1) Å compared with the x-ray value of 1.802(2) Å.

5) Quadrupole Coupling Strengths The nonzero nuclear quadrupole moments of the isotopes of the B and Cl nuclei cause measurable splittings of the microwave transitions for 1-chloroborepin. From the analysis of the high-resolution spectra, the quadrupole coupling strengths were obtained for the B and Cl nuclei in three isotopologues (11B35Cl, 10B35Cl, and 11B37Cl) and these fit parameters are listed in Table 7. In the case of the fitting of the 11B37Cl isotopologue, the 11B quadrupole coupling strengths were held fixed to the parameters obtained in the


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fit of 11B35Cl. Some transitions were measured for a 10B37Cl isotopologue, but there were not enough transitions to obtain a decent fit of the spectroscopic parameters. Table 7 also lists all of the quadrupole coupling strengths obtained from the geometry optimization calculations as a comparison. Past experiments have shown that 1-chloroborepin is a slightly aromatic molecule. To further study the aromatic character of this molecule based on the electronic structure around the boron atom, the valence p-orbital occupations can be determined with the quadrupole coupling parameters of the molecule obtained from the microwave spectra. Boron typically has three valence electrons which are capable of making three sigma bonds using three sp2 hybridized orbitals, leaving the p-orbital unoccupied. Any electron density determined to be in its valence p-orbital can be contribute to the molecule’s aromatic character. The electron density in the valence porbital on B may be a result of donation from the electron rich Cl atom. The absence of electron density in the valence p-orbital on Cl can be determined with the same analysis and the results compared to determine the electron density around each of these nuclei. In order to determine the valence p-orbital electron density, an extended Townes-Dailey analysis was performed with the experimental parameters determined from the microwave spectra. The mathematical details describing the analysis for all types of hybridized orbitals is documented well in the literature.24 In order to perform the analysis, it is necessary to know the quadrupole coupling strengths of the nuclei involved with just one valence p-electron. These quadrupole coupling strengths can be found in the text by Gordy and Cook35 and for 11B the value is -5.4 MHz and for 35Cl it is 109.74 MHz. Because the expressions used to determine the electron occupations in



the hybridized orbitals are underdetermined, meaning that there are not enough parameters to solve for each valence orbital occupation, chemically reasonable solutions must be chosen in the analysis – for example a result cannot give more than two electrons in any given orbital. Each hybridization model (sp3, sp2, and sp) was used for the 35Cl analysis, but after calculating some results, the sp3 model seemed to provide the most chemically reasonable solutions to the equations. The sp2 model was used for 11B as the geometry is planar and it was determined from previous experiments that 1-chloroborepin has a slight aromatic character, so boron must have a p-orbital to interact with the rest of the molecule’s delocalized π-electrons. The results from the extended Townes-Dailey analyses and the NBO calculations are listed in Tables 8 and 9 respectively for 11B and 35Cl.

6) Discussion The microwave spectra were measured for three isotopologues of 1chloroborepin (11B35Cl, 10B35Cl, and 11B37Cl) and the measured transitions are listed in Tables 1-3. From the measured transitions, microwave fits were performed to obtain the rotational constants and quadrupole coupling strengths of the B and Cl nuclei in the molecule. For each isotopologue, these fit parameters are listed in Table 4. The centrifugal distortion constants were not obtained in the fit due to the transitions measured being of low J values so these transitions would not be sufficient to accurately describe the distortion in the molecule. From these rotational constants determined from the microwave fits, a least squares structure fitting routine was used to obtain the structural parameters around the B nucleus. There were two varied


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parameters that were fit using nine experimental rotational constants. These varied parameters represented the movement of the C-H groups adjacent to the B nucleus along the b-axis and the Cl nucleus was varied along the a-axis, as depicted in Figure 1. The calculated rotational constants of this best fit structure are listed with each of the experimentally determined values in Table 6. The standard deviation of the structure fit was 0.56 MHz (this is the deviation of the calculated rotational constants from the obtained best fit structure with the experimentally determined values obtained from the fit of the spectra), which is quite small compared to the magnitudes of the rotational constants of the molecule and so the obtained structure from the fit is a reasonable representation of 1-chloroborepin in the gas phase. The B-Cl and B-C bond lengths determined in the structure fit are 1.798(1) Å and 1.533(10) Å respectively. The larger error on the B-C bond length is due to there being an absence of 13C isotopologue data. The B-Cl bond length is slightly smaller than what was obtained in the crystal structure (1.802(2) Å) and the B-C bond length is 0.019 Å larger than the crystal (1.514(1) Å). The B-C bond length obtained in the structure fit resembles the B-C bond length of 4a,8aazaboranaphthalene (1.510 Å) which was previously determined to exhibit aromatic character. Typical B-C single bond lengths are ~1.55-1.58 Å36 and the obtained B-C bond length of 1.533(10) Å in the gas phase structure is indicative of some π-bonding between B and C. As was determined in the X-ray crystal structure of the molecule, the C-C bond lengths were also indicative of π-bonding interactions and during the structure fitting process, the C-C bond lengths were held fixed to these X-ray values. In addition to having bond lengths indicative of π-bonding, a second structural criteria of aromatic molecules is that the molecule needs to be planar, and the planarity of molecules can



be directly determined from the inertial defect calculated with the experimental rotational constants of the molecule. 1-chloroborepin is planar as indicated by a small value of the inertial defect which is close to zero (-0.174 amu Å2). The relatively small variations in the ring atom bond lengths also indicate some aromatic character for this molecule. After further study, even more information about the aromatic character of 1chloroborepin can be obtained by determining the valence p-orbital occupation of the empty p-orbital on the B nucleus. To determine the electron occupations in these valence orbitals, the extended Townes-Dailey analysis was performed using the experimental values of the quadrupole coupling strengths of both the 11B and 35Cl nuclei. Due to the expressions to determine the electron occupations being underdetermined as a result of there being two independent quadrupole coupling parameters for the nucleus, chemically reasonable results needed to be chosen. The analysis was performed for 11B by varying the occupation of the p-orbital manually (first row in Table 8), which provided results for the electron occupations in the sp2 orbital forming the single bond with Cl (second row) and the sum of electron occupations in the two sp2 orbitals creating the two single bonds with the adjacent C atoms (third row). The results from the analysis for the 11B nucleus are listed in Table 8. Also shown in Table 8 are the total valence electrons and the charge associated with each result. For the 11B nucleus, a sp2 hybridized model was used due to the planarity of the molecule as well as the aromatic character previously determined to be present within the molecule. Table 8 also contains the natural bond orbital (NBO) calculated results of the valence electron occupations using B3LYP/aug-cc-pVQZ. The values in bold from the TownesDailey analysis are the values that agree with the NBO calculated results the best. It


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can be seen in Table 8 that one result from the Townes-Dailey analysis agreed very well with the NBO calculation and that is when there are 0.50 electrons in the valence porbital, 0.67 electrons in the sp2 orbital forming the single bond with Cl, and a total of between 1.2 and 1.4 electrons in the two sp2 orbitals making the adjacent single bonds with C. The total valence electron occupation is then 2.36 electrons with a formal charge of 0.64, which is reasonable for the B nucleus. As there are no π-bonds adjacent to the B nucleus to share any electron density with its valence p-orbital, it was thought that some of the electron density might come from the valence orbitals on the Cl nucleus to supply B with enough electron density to exhibit aromatic behavior. A similar Townes-Dailey analysis was carried out for the 35Cl nucleus and these results are listed in Table 9. Three different Townes-Dailey analyses were performed to determine which hybridized model for Cl (either sp3, sp2, or sp) provided the best and most chemically reasonable results. The electron occupations obtained from the sp3 analysis seemed to provide the results with the best agreement to the calculation. After comparing the NBO calculated results with the results from the Townes-Dailey analysis, it seemed that there were a range of electron occupations that agreed with the calculations. This was when there are 1.35 electrons determined to be in the sp3 orbital forming the single bond with B (this was the value that was manually chosen in the Cl analysis). Even though the 35Cl results do not agree with the NBO calculation as well as in the case of 11B, it can be seen in Table 9 that the sp3 orbital out of plane along the c-principal axis has a slightly less electron occupation than the two other symmetric sp3 orbitals that the other lone pairs occupy, 1.98 electrons in each of the symmetric orbitals where as there are less than 1.9 electrons in the orbital out of



plane (according to Townes-Dailey results there are about 1.7 electrons in this orbital). Because this orbital with one of the lone pairs of Cl is less than what was determined for the two other symmetric orbitals, there is probably sufficient overlap of the valence porbital on B and the sp3 hybridized orbital on Cl such that Cl can donate electron density into B’s p-orbital to provide 1-chloroborepin with its slightly aromatic character.

7) Conclusions The gas phase structure of 1-chloroborepin was refined using the measured microwave spectra for 3 isotopologues to obtain structural parameters near the B nucleus. The B-C bond length was determined to be is 1.533(10) Å and the B-Cl bond length is 1.798(1) Å. A Townes-Dailey analysis using the determined quadrupole coupling strengths of both 11B and 35Cl showed that Cl is sharing electron density with the empty p-orbital on B to give 1-chloroborepin its slight aromatic character.

Acknowledgements This material is based upon work supported by the National Science Foundation under Grant No. CHE-1057796 at the University of Arizona.

References 1. Wade, C.R.; Broomsgrove, A.E.J.; Aldridge, S.; Gabbaï, F.P. Fluoride Ion Complexation and Sensing using Organoboron Compounds. Chem. Rev. 2010, 110, 3958–3984. 2. Jakle, F. Advances in the Synthesis of Organoborane Polymers for Optical, Electronic, and Sensory Applications. Chem. Rev. 2010, 110, 3985–4022. 14 ACS Paragon Plus Environment

Page 14 of 31

Page 15 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3. Liu, L.; Marwitz, A.J.V.; Mathews, B.W.; S.Y. Liu. Boron Mimetics: 1,2-Dihydro-1,2Azaborines Bind inside a Nonpolar Cavity of T4 Lysozyme. Angew. Chem. Int. Ed. 2009, 48, 6817. 4. Abbey, E.R.; Zakharov, L.N.; Liu, S. Electrophilic Aromatic Substitution of a BN Indole. J. Am. Chem. Soc. 2010, 132, 16340. 5. Matsumi, N.; Chujo, Y. π-Conjugated Organoboron Polymers via the Vacant p-Orbital of the Boron Atom. Polym. J. 2008, 40, 77–89. 6. Lin, N.; Zhao, X.; Cheng, X.; Jiang, M. Quantum Chemical Investigation on One- and Two-Photon Absorption Properties for a Series of Donor-π-Acceptor-Type Compounds with Trivalent Boron as an Acceptor. J. Mol. Struct.: THEOCHEM. 2007, 820, 98–106. 7. Entwistle, C.D.; Marder, T.B. Applications of Three-Coordinate Organoboron Compounds and Polymers in Optoelectronics. Chem. Mater. 2004, 16, 4574–4585. 8. Hudnall, T. W.; Chiu, C.W.; Gabbaï, F.P. Fluoride Ion Recognition by Chelating and Cationic Boranes. Acc. Chem. Res. 2009, 42, 388–397. 9. Zhou, G.; Baumgarten, M.; Mullen, K. Mesitylboron-Substituted Ladder-Type Pentaphenylenes: Charge-Transfer, Electronic Communication, and Sensing Properties. J. Am. Chem. Soc. 2008, 130, 12477–12484. 10. Hudnall, T.W.; Gabbaï, F.P. Ammonium Boranes for the Selective Complexation of Cyanide or Fluoride Ions in Water. J. Am. Chem. Soc. 2007, 129, 11978–11986. 11. Yamaguchi, S.; Wakamiya, A. Boron as a Key Component for New π-Electron Materials. Pure Appl. Chem. 2006, 78, 1413–1424. 12. Nagai, A.; Kokado, K.; Nagata, Y.; Chujo, Y. 1,3-Diketone-Based Organoboron Polymers: Emission by Extending π-Conjugation along a Polymeric Ligand. 15 ACS Paragon Plus Environment


Macromolecules. 2008, 41, 8295. 13. Wakamiya, A.; Mori, K.; Yamaguchi, S. 3-Boryl-2,2’-bithiophene as a Versatile Core Skeleton for Full-Color Highly Emissive Organic Solids. Angew. Chem. Int. Ed. 2007, 46, 4273–4276. 14. Qin, Y.; Kiburu, I.; Shah, S.; Jakle, F. Luminescence Tuning of Organoboron Quinolates Through Substituent Variation at the 5-Position of the Quinolato Moiety. Org. Lett. 2006, 8, 5227–5230. 15. Craze, G.A.; Kirby, A.J.; Osborne, R. Bimolecular Nucleophilic Substitution on an Acetal. J. Chem. Soc., Perkin Trans. 2. 1978, 357-368. 16. Knier, B.L.; Jencks, W.P. Mechanism of Reactions of N-(Methoxymethyl)-N,NDimethylanilinium Ions with Nucleophilic Reagents. J. Am. Chem. Soc. 1980, 102, 67896798. 17. Richard, J.P.; Jencks, W.P. Concerted Bimolecular Substitution Reactions of 1Phenylethyl Derivatives. J. Am. Chem. Soc. 1984, 106, 1383-1396. 18. Dietz, P.E.; Jencks, W.P. Swain-Scott Correlations for Reactions of Nucleophilic Reagents and Solvents with Secondary Substrates. J. Am. Chem. Soc. 1986, 108, 4549-4555. 19. Vol'pin, M. E. Non-Benzenoid Aromatic Compounds and the Concept of Aromaticity. Russ. Chem. Rev. (Engl. Transl.) 1960, 29, 129. 20. Messersmith, R.E.; Tovar, J.D. Assessment of the Aromaticity of Borepin Rings by Spectroscopic, Crystallographic and Computational Methods: a Historical Overview. J. Phys. Org. Chem. 2015, 28, 378–387. 21. Ashe III, A.J.; Klein, W.; Rousseau, R. Evaluation of the Aromaticity of Borepin: 16 ACS Paragon Plus Environment

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Synthesis and Properties of 1-Substituted Borepins. Organometallics. 1993, 12, 32253231. 22. Ashe III, A.J.; Kampf, J.W.; Klein, W.; Rousseau, R. Structural Evidence of the Aromaticity of Borepins: A Comparison of 1-Chloroborepin and Tricarbonyl(1Chloroborepin)Molybdenum. Angew. Chem. Int. Ed. 1993, 32, 1065-1066. 23. Larsen, N.W.; Hansen, S.R.; Pedersen, T. Planarity of 1-Chloroborepin. J. Mol. Struct. 2006, 780–781, 317–318. 24. Novick, S.E. Extended Townes-Dailey Analysis of the Nuclear Quadrupole Coupling Tensor. J. Mol. Spectrosc. 2011, 267, 13-18. 25. Pejlovas, A.M.; Daly, A.M.; Ashe III, A.J.; Kukolich, S.G. Microwave spectra, Molecular Structure, and Aromatic Character of 4a,8a-Azaboranaphthalene. J. Chem. Phys. 2016, 144, 114303. 26. Daly, A.M.; Tanjaroon, C.; Marwitz, A.J.V.; Liu, S.; Kukolich, S.G. Microwave Spectrum, Structural Parameters, and Quadrupole Coupling for 1,2-Dihydro-1,2Azaborine. J. Am. Chem. Soc. 2010, 132, 5501–5506. 27. Ashe III, A.J.; Kampf, J.W.; Nakadaira, Y.; Pace, J.M. Aromatic Boron Heterocycles: Generation of 1H-Borepin and Structure of Tricarbonyl(1-Phenylborepin)Molybdenum. Angew. Chem. Int. Ed. Engl. 1992, 31, 1255-1258. 28. Bumgarner, R.E.; Kukolich, S.G. Microwave Spectra and Structure of HI-HF Complexes. J. Chem Phys. 1987, 86, 1083. 29. Tackett, B.S.; Karunatilaka, C.; Daly, A.M.; Kukolich, S.G. Microwave Spectra and Gas-Phase Structural Parameters of Bis(η5-Cyclopentadienyl)Tungsten Dihydride. Organometallics. 2007, 26, 2070-2076. http://dx.doi.org/10.1021/om061027f 17 ACS Paragon Plus Environment


30. Frisch, M.J; Trucks, G.W.; Schlegel, H.B.; Scuseria, G.E.; Robb, M.A.; Cheeseman, J.R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G.A., et al. Gaussian 09, Revision A.1; Gaussian, Inc.: Wallingford, CT 2009. 31. Pickett, H.M. The Fitting and Prediction of Vibration-rotation Spectra with Spin Interactions. J. Mol. Spectrosc. 1991, 148, 371. 32. Kisiel, Z. Programs for Rotational Spectroscopy. http://www.ifpan.edu.pl/~kisiel/struct/struct.htm#pmifst (accessed Janurary 24, 2018). 33. Bohn, R. K.; Montgomery Jr.; J. A.; Michels, H. H.; Fournier, J. A. Second Moments and Rotational Spectroscopy. J. Mol. Spectrosc. 2016, 325, 42-49. 34. Oka, T. On Negative Inertial Defect. J. Mol. Struct. 1995, 352-353, 225-233. 35. Gordy, W.; Cook, R.L. Microwave Molecular Spectra; Wiley-Interscience, New York, U.S.A., 1984. 36. Bartell, L.S.; Carroll, B.L. Electron-Diffraction Study of the Structure of B(CH3)3. J. Chem. Phys. 1965, 42, 3076.


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SnBu 2

+ BCl3

BCl

1,1-Dibutyl-1H-stannepin

1-Chloro-1H-borepin

Scheme 1. Synthesis of 1-Chloro-1H-borepin.


+ Bu2SnCl2


Page 20 of 31

Figure 1. The best fit structure obtained for 1-chloroborepin. The molecule is symmetrical along the a-axis and so only half of the structural parameters are shown. The fit bond lengths are r(B-Cl) = 1.798 Å and r(B-C5 or C6) = 1.533 Å.

Table 1. Measured microwave transitions and the deviations from the calculated values for the 11B35Cl isotopologue of 1-chloroborepin. All values are shown in MHz. Quantum number assignments J′ Ka’ Kc’ F1’ F’ J″ Ka” Kc” F1” F” 3 1 3 3 3 2 1 2 1 2 3 1 3 5 5 2 1 2 4 5 3 1 3 4 4 2 1 2 3 4 3 1 3 4 3 2 1 2 4 2 3 1 3 4 4 2 1 2 4 3 3 1 3 3 3 2 1 2 4 3 3 1 3 4 4 2 1 2 4 4 3 1 3 4 3 2 1 2 2 3 3 1 3 4 4 2 1 2 3 3 3 1 3 4 2 2 1 2 3 2 3 1 3 3 1 2 1 2 2 1 3 1 3 5 3 2 1 2 3 3 3 0 3 4 2 2 0 2 4 2 3 0 3 5 3 2 0 2 4 2 3 0 3 2 0 2 0 2 1 1 3 0 3 4 3 2 0 2 2 2 3 0 3 3 2 2 0 2 3 1 3 0 3 5 4 2 0 2 4 3 3 0 3 2 1 2 0 2 2 0 3 0 3 3 4 2 0 2 2 3 3 0 3 2 3 2 0 2 1 2 3 0 3 2 3 2 0 2 3 4 3 0 3 4 4 2 0 2 4 4 3 0 3 3 3 2 0 2 3 2 3 0 3 3 3 2 0 2 3 3 3 0 3 5 5 2 0 2 4 4 3 0 3 2 2 2 0 2 2 1 3 0 3 2 2 2 0 2 3 2 3 0 3 2 2 2 0 2 3 3 3 0 3 4 3 2 0 2 3 3 3 0 3 5 4 2 0 2 4 4 3 0 3 2 1 2 0 2 2 1

11 35

B Cl

νobs 5637.405 5638.076 5638.121 5638.279 5638.351 5638.566 5639.880 5639.969 5640.153 5646.453 5646.722 5647.030 5988.151 5988.324 5988.475 5988.642 5988.712 5988.757 5988.835 5990.616 5990.735 5990.885 5991.003 5991.085 5991.115 5991.171 5991.199 5991.244 5991.276 5994.946 5995.031 5995.088


νo-c -0.001 -0.002 -0.003 0.008 -0.007 0.003 -0.003 -0.004 0.001 0.017 -0.003 -0.022 0.004 0.015 0.005 0.003 -0.003 -0.012 -0.002 0.003 -0.002 0.005 -0.001 -0.002 0.006 0.005 -0.006 -0.002 0.008 -0.006 -0.009 0.003

Page 21 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 5 5 5 5 5 5 5 5 5 5

0 2 1 1 1 1 0 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0

3 2 2 2 2 4 4 4 4 4 4 3 3 3 3 5 5 5 5 5 5 5 5 5 5

2 3 2 4 5 5 5 5 3 4 3 3 3 5 4 5 7 5 6 6 5 6 4 5 5

1 4 2 3 5 3 3 3 1 3 2 3 1 4 2 4 6 3 4 5 6 5 2 4 5

2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4

0 2 1 1 1 1 0 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0

2 1 1 1 1 3 3 3 3 3 3 2 2 2 2 4 4 4 4 4 4 4 4 4 4

3 2 2 3 4 3 5 4 2 3 2 3 3 5 4 4 6 4 5 6 6 5 5 5 4

2 3 2 4 4 2 3 2 0 2 1 3 1 4 2 3 5 2 3 5 7 4 3 4 4

5995.139 6092.540 6500.192 6502.684 6505.459 7499.860 7877.309 7877.475 7877.685 7878.082 7878.252 8642.078 8642.116 8642.148 8642.208 9330.744 9330.899 9331.020 9694.182 9694.493 9694.631 9694.789 9694.895 9694.955 9695.506

0.013 0.004 -0.009 0.012 0.020 0.008 0.000 0.003 0.015 -0.016 -0.001 -0.014 -0.002 -0.005 -0.005 -0.022 0.010 0.008 -0.001 0.004 -0.012 0.004 -0.000 0.002 0.001

Table 2. Measured microwave transitions and the deviations from the calculated values for the 10B35Cl isotopologue of 1-chloroborepin. All values are shown in MHz. Quantum number assignments J′ Ka’ Kc’ F1’ F’ J″ Ka” Kc” F1” F” 3 1 3 3 3 2 1 2 2 3 3 1 3 4 4 2 1 2 2 4 3 1 3 6 7 2 1 2 5 7 3 1 3 2 2 2 1 2 2 3 3 1 3 3 3 2 1 2 2 4 3 1 3 3 2 2 1 2 1 3 3 1 3 2 2 2 1 2 4 3 3 1 3 4 3 2 1 2 1 2 3 1 3 3 4 2 1 2 2 3 3 1 3 2 3 2 1 2 3 2 3 1 3 6 5 2 1 2 3 5 3 0 3 5 4 2 0 2 5 4 3 0 3 5 4 2 0 2 1 3

10 35

B Cl

νobs 5637.758 5637.916 5637.962 5638.167 5638.202 5638.758 5639.230 5639.406 5639.514 5646.651 5647.369 5988.092 5988.104


νo-c 0.003 0.005 -0.003 0.010 -0.010 -0.000 -0.006 0.001 0.000 0.003 0.005 -0.011 0.002


3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4

2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 1 1 1 1 0 2 0 2 1 1 1

1 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 1 3 3 3 3 3 2 2 4 4 4 2 4 2 3 3 3

3 6 0 4 3 3 2 3 3 2 2 1 1 4 1 1 3 6 6 2 5 6 3 6 5 4 5 3 6 2 2 5 5

3 5 2 5 4 2 1 5 5 4 3 2 2 4 1 1 3 5 6 1 4 5 2 7 7 6 4 3 6 2 1 5 5

2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 2 0 0 2 1 1 1

2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 1 1 3 3 1 3 3 1 2 2 2

1 5 1 2 4 2 2 3 4 3 1 1 2 3 2 3 3 3 4 3 4 5 4 5 6 6 3 5 6 3 2 4 4

3 4 3 4 3 2 2 4 6 4 2 2 3 3 1 2 4 5 5 2 3 5 3 6 7 7 3 4 6 3 1 4 5

Page 22 of 31

5988.220 5988.349 5988.483 5988.626 5988.631 5988.853 5988.918 5990.597 5990.606 5990.724 5990.747 5990.906 5990.952 5991.077 5991.332 5991.355 5994.569 5994.745 5995.189 5995.224 5996.933 5997.157 6504.517 6505.383 7499.621 7499.761 7877.398 7877.752 7877.896 7877.941 8641.599 8641.875 8641.926

-0.001 -0.006 0.012 -0.004 -0.004 0.013 -0.009 0.009 -0.004 -0.004 -0.000 0.015 -0.011 0.001 0.005 -0.002 -0.008 -0.009 0.013 0.001 0.012 -0.016 -0.010 0.012 0.003 -0.008 0.007 -0.003 -0.003 0.002 0.010 -0.012 0.002

Table 3. Measured microwave transitions and the deviations from the calculated values for the 11B37Cl isotopologue of 1-chloroborepin. All values are shown in MHz. Quantum number assignments J′ Ka’ Kc’ F1’ F’ J″ Ka” Kc” F1” F” 3 0 3 4 4 2 0 2 3 4

11 37

B Cl

νobs 5842.028


νo-c -0.008

Page 23 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3 3 3 3 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 5 5 5 5 5 5 5 5 5 5 5 5 5

0 0 0 0 1 1 1 1 1 1 1 1 1 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0

3 3 3 3 4 4 4 4 4 4 4 4 4 4 4 4 4 4 3 3 3 3 3 5 5 5 5 5 5 5 5 5 5 5 5 5

2 3 4 5 5 6 5 6 5 6 4 4 6 5 4 6 5 6 4 3 6 6 5 6 7 7 5 5 7 4 5 7 6 6 7 5

0 2 4 5 3 4 6 7 4 5 3 2 4 5 4 6 4 5 3 1 4 5 3 4 7 5 5 6 8 2 4 5 4 5 8 4

2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 4 4 4

0 0 0 0 1 1 1 1 1 1 1 1 1 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0

2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 2 2 2 2 2 4 4 4 4 4 4 4 4 4 4 4 4 4

1 3 3 4 4 5 4 5 4 5 3 2 5 4 4 5 4 5 4 3 5 5 4 5 6 6 5 4 6 4 4 6 5 6 6 4

1 1 3 4 2 3 5 6 4 5 3 2 4 4 4 5 4 5 3 1 3 5 3 3 6 4 5 5 7 2 4 5 3 5 7 4

5847.027 5847.180 5849.029 5849.116 7325.671 7325.875 7325.954 7326.001 7326.764 7326.861 7326.920 7329.145 7329.311 7700.252 7700.341 7700.393 7702.451 7702.595 8417.152 8417.489 8417.788 8420.674 8425.253 9121.926 9122.000 9122.035 9122.125 9122.152 9122.242 9122.645 9123.317 9126.113 9483.618 9483.796 9484.354 9486.368

-0.002 0.008 0.016 -0.013 -0.013 0.006 0.014 -0.013 -0.003 -0.007 0.004 -0.008 -0.006 0.005 -0.004 -0.007 -0.003 0.013 0.001 0.012 -0.004 0.001 -0.008 -0.013 -0.001 -0.004 0.013 0.001 0.014 0.007 0.012 0.003 -0.008 -0.009 -0.004 0.004

Table 4. Molecular constants obtained from fitting the measured microwave transitions for each of the 1-chloroborepin isotopologues measured. Parameter

11 35

B Cl


10 35

B Cl

11 37

B Cl


Page 24 of 31

A /MHz

3490.905(35)

3491.210(61)

3490.56453a

B /MHz

1159.38520(79)

1159.38970(88)

1127.08000(85)

C /MHz

870.59492(56)

870.59300(66)

852.23300(39)

1.5χaa (B) /MHz

-0.220(22)

-0.394(43)

-0.220b

0.25(χbb – χcc) (B) /MHz

-1.5300(99)

-3.207(18)

-1.5300b

1.5χaa (Cl) /MHz

-54.572(33)

-54.945(33)

-43.500(33)

0.25(χbb – χcc) (Cl) /MHz

4.7740(79)

4.7870(88)

3.800(10)

N

58

46

37

σ /kHz

8

8

9

a) This A rotational constant was held fixed to the predicted value during the microwave fit of this isotopologue. b) The 11B quadrupole coupling strengths were held fixed to the values obtained in the 11 35 B Cl fit.

Table 5. Experimental and calculated rotational constants and second moments of 1chloroborepin. Experimental

B3LYP/aug-cc-

MP2/aug-cc-

CCSD/aug-cc-

pVQZ

pVQZ

pVDZ

A /MHz

3490.905(35)

3532.4663

3532.0588

3436.1104

B /MHz

1159.38520(79) 1153.8854

1159.1417

1136.7949

C /MHz

870.59492(56)

869.77282

872.73115

854.19496

Paa /amu Å2

435.8154

437.9802

435.9941

444.5648

Pbb /amu Å2

144.6830

143.0669

143.0834

147.0788

Pcc /amu Å2

0.08716

0.000003

0.00001

-0.000009

∆ /amu Å2

-0.174

-0.000006

-0.00002

0.00002


Page 25 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 6. The fit rotational constants compared with the calculated values of the best fit structure. The standard deviation of the structure fit is 0.562 MHz.a *This rotational constant was held fixed to a predicted value for that isotopologue. Parameter

Fit Rotational Constants

Calculated Deviation from rotational constants Measured Values of best fit structure 11 35 B Cl A 3490.905(35) 3490.905 0.000 B 1159.385(79) 1159.048 0.337 C 870.595(56) 870.144 0.451 10 35 B Cl A 3491.210(61) 3490.905 0.305 B 1159.390(88) 1160.465 -1.075 C 870.593(66) 870.942 -0.349 11 37 B Cl A 3490.565* 3490.905 -0.340 B 1127.080(85) 1126.654 0.427 C 852.233(39) 851.758 0.475 a) The deviation of the calculated rotational constants from the obtained best fit structure with the experimentally determined values obtained from the fit of the spectra.

Table 7. Quadrupole coupling strengths determined from the microwave fits for three isotopologues of 1-chloroborepin. Also shown are the calculated values for each of the isotopologues using B3LYP/aug-cc-pVTZ. Quadrupole

11 35

10 35

B Cl

B Cl

11 37

B Cl

Coupling Parameters (fit values) 1.5χaa (B)

-0.220(22)

-0.394(43)

-0.220*

0.25(χbb – χcc) (B)

-1.5300(99)

-3.207(18)

-1.5300*

1.5χaa (Cl)

-54.572(33)

-54.945(33)

-43.500(33)



0.25(χbb – χcc) (Cl)

4.7740(79)

4.7870(88)

11 35

Quadrupole

Page 26 of 31

3.800(10)

10 35

B Cl

11 37

B Cl

B Cl

Coupling Parameters (calculated values) 1.5χaa (B)

-0.116

-0.242

-0.116

0.25(χbb – χcc) (B)

-1.6257

-3.388

-1.626

1.5χaa (Cl)

-55.082

-55.082

-43.411

0.25(χbb – χcc) (Cl)

4.7924

4.7924

3.777

Table 8. Orbital occupations of 11B using an extended Townes-Dailey analysis with a sp2 hybridized model. Also shown are the NBO calculated values for each of the orbitals with B3LYP/aug-cc-pVQZ. The bolded values are the similar values between the calculation and the results using experimental parameters. 11

B sp2

pc-orba

Electron occupations resulting from the Townes-Dailey analysis in each valence sp2 hybridized orbital on the 11B nucleus after choosing the occupation in the pc-orb (first row) on the 11B nucleus. 0.50 0.20 0.30 0.40 0.60 0.70

B-Clb

0.37

0.47

0.57

0.67

0.77

0.87

0.63

B-C (sum)c

0.60

0.80

1.00

1.20

1.40

1.60

1.35

Total

1.16

1.56

1.96

2.36

2.76

3.16

2.45

Occupation d


NBO

0.47

Page 27 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Chargee

1.84

1.44

0.64

1.04

0.24

-0.16

0.55

a) Electron occupation in the empty p-orbital on 11B. These occupations were varied between 0 to 2 electrons. b) The resulting electron occupations in the sp2 hybridized orbital on 11B forming the single bond with the Cl nucleus. c) The sum of the resulting electron occupations in the equivalent sp2 hybridized orbitals on 11B forming the single bonds with the two C nuclei. d) The sum of the electron occupations in a-c. e) The total charge on 11B taking into account its 3 valence electrons.

Table 9. Orbital occupations of 35Cl using an extended Townes-Dailey analysis with a sp3 hybridized model. Also shown are the NBO calculated values for each of the orbitals with B3LYP/aug-cc-pVQZ. The bolded values are the similar values between the calculation and the results using experimental parameters. 35

Cl sp3

B-Cla

Electron occupations resulting from the Townes-Dailey analysis in each valence sp3 hybridized orbital on the 35Cl nucleus after choosing the occupation in the bonding sp3-orb with 11B (first row) on the 35Cl nucleus. 1.35 1.10 1.20 1.30 1.40 1.50

Lone pair

1.48

1.58

1.68

1.73

1.78

1.88

1.87

3.70

3.90

4.10

4.20

4.30

4.50

3.95

6.28

6.68

7.08

7.28

7.48

7.88

7.18

0.72

0.32

-0.08

-0.28

-0.48

-0.88

-0.18

NBO

1.36

(sp3 in a-c plane)b sum of equivalent lone pairsc Total occupationd Chargee

a) Electron occupation in the sp3-orbital on 35Cl forming the single bond with the B nucleus. These occupations were varied between 0 to 2 electrons.



b) The resulting electron occupation in the sp3 hybridized orbital on 35Cl which is the lone pair in the a-c plane. c) The sum of the resulting electron occupations in the two equivalent sp3 hybridized orbitals which are the lone pairs on either side of the 35Cl nucleus (looking down on the a-b plane). d) The sum of the electron occupations in a-c. e) The total charge on 35Cl taking into account its 7 valence electrons.


Page 28 of 31

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Figure 2. The best fit structure obtained for1-chloroborepin. The molecule is symmetrical along the a-axis and so only half of the structural parameters are shown. The fit bond lengths are r(B-Cl) = 1.798 Å and r(BC5 or C6) = 1.533 Å. 214x186mm (72 x 72 DPI)

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Figure 1. Synthesis of 1-Chloro-1H-borepin. 147x39mm (300 x 300 DPI)


Page 30 of 31

Page 31 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


251x98mm (72 x 72 DPI)


Microwave Spectra, Structure, and the Aromatic Character of 1

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