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Determination of the crystal structure of the hydrobromide of 3-carbomethody-trans-3, 5-dimenthyl-D-pyrazoline by X-ray diffraction Luth, Hartwig

Abstract

The hydrobromide of 3-carbomethoxy-trans-3, 5-dimethyl-Δ¹-pyrazoline, C₇H₁₃N₂O₂Br, crystallises in the monoclinic system with a = 8.28, b = 10.31, c = 13.92Å and β = 122.4°. The space group is P2₁/c and there are four molecules per unit cell, thus each molecule forms an asymmetric unit in the cell. The intensities of 580 reflections were estimated from films exposed to CuK α radiation. The structure determination was based on the heavy atom Patterson and Fourier methods and least squares refinement. The final discrepancy, R, for the 409 observed reflections is 0.116. The compound was found to contain a bromide ion and a cation with no double bond, with a trigonal C(5) atom, and a positive charge distributed between N(1) and C(5). The five-membered ring is non-planar with N(2) displaced 0.32 Å from the plane of the remaining four atoms, or N(1) and N(2) displaced above and below the plane of the three carbon atoms and the methyl group on C(5) lying almost on these planes. All other molecular dimensions are normal. The shortest intermolecular approach is a C(5)...O(3) distance of 2.76 Å, which results from the attraction between the positively-charged carbon and the relatively negative oxygen. The shortest approach involving a bromide ion is a Br⁻•••H-N(2) hydrogen bond of 3.22 Å; the next shortest approach is a Br⁻•••N(2) distance of 3.31 Å. The other intermolecular distances are normal.

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