A"study of boron trifluoride complexes with stigmasterol (1), androstanolone (2), androsterone (3), testosterone (4), nortestosterone (5), androstenedione (6), and progesterone (7) has been carried out by direct, low-temperature , 13C, and 19F nuclear magnetic resonance methods. A consideration of the 1H and 19F NMR spectra of the complexes led to an identification of the primary interaction site in each steroid. The steroid functional group basicities decrease in the order OH > 0=0 (a,8 unsaturated) > 0=0 (saturated). In five of the systems, complex formation occurs at one site in the ligand, whereas competitive complexation was evident in solutions of 4 and 5. The 18C NMR spectrum of BF3-6 was interpreted in terms of possible electron density changes occurring in the molecule.Solutions of a variety of organic bases with boron trihalides have been investigated by calorimetric3""7 and spectro-scopic8-18 techniques to evaluate the heats of formation of the complexes and their structural features. The more recent measurements of these acid-base systems have utilized direct, low-temperature nuclear magnetic resonance (NMR) methods.19-27 In the presence of excess base and at temperatures low enough to reduce the rate of exchange, it is possible to observe separate resonance signals for bulk and coordinated ligand. This observation leads to an accurate measure of the 7 , 11B, 13C, and 19F NMR chemical shift changes produced by complex formation and the stoichiometry of the complex, a qualitative estimate of steric factors, an evaluation of the ligand preference of a boron trihalide in a mixture of bases, and a determination of the most active site in complicated molecules. These features have been evaluated for amines and phosphines,19 oxygencontaining bases,20-21 pyridines22,23 and other nitrogen heterocycles,24 esters,25 cyclic ketones,26,28,29 several ethers,27 and three steroids.30 Steroids are of interest from the viewpoints of their physiological importance, and their structural features, particularly, the multiple potential sites for interaction with Lewis acids. Since it has been demonstrated that this low-temperature NMR technique is particularly well suited for identifying principal interaction sites in molecules,25,30 this approach was used here. The steroids chosen were stigmasterol and several androgens, namely, androstanolone, androstenedione, androsterone, 19-nortestosterone, progesterone, and testosterone (see structures). Experimental SectionMethods. The boron trifluoride was CP grade (J. T. Baker) and 99.5% pure. The dichloromethane solvent and 2-cyclohexeu-l-one were reagent grade and they were dried over CaSO* before use. The steroids were purchased from Steraloids, Inc., and they were used as received. The purity of the steroids was verified by the absence of extraneous carbon-13 (13C NMR) signals and the dryness of each sample was checked by the absence of a 19F NMR signal for the BF3-H2O adduct. The BF3 was fractionated twice at -100°a nd condensed in vacuo in the NMR sample tube (Wilmad Glass C...

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Cation coordination number measurements of AlCl3, AlBr3, Al(ClO4)3, Al(NO3)3, BeCl2, GaCl3, GA(ClO4), InCl3, In(Cl)4)3, and Mg(ClO4)2, in water, and in aqueous acetone mixtures have been carried out by a proton magnetic resonance method. At low temperatures, solutions of these electrolytes exhibit separate proton resonance signals for bulk water, and water molecules in the first solvation shell of the cation. Integration of these signals provides a direct measure of the coordination number of the cation. The Al(III) and Ga(III) are solvated by six water molecules in all solutions, regardless of the anion present. The Be(II) is coordinated by four water molecules in water and in aqueous acetone mixtures. The In(III) and Mg(II) could only be studied in aqueous acetone mixtures, wherein they are each coordinated by six water molecules. With the possible exception of Be(II) no evidence for contact ion pairing was found.

A cation hydration number study has been carried out for solutions of UO2(C104)2, U02(N03)2, U02C12, and U02Br2 in water-acetone mixtures by the direct proton magnetic resonance (pmr) method. At temperatures below -85°, proton exchange is slow enough to permit the observation of separate pmr signals for bulk water molecules and water molecules in the U022+ solvation shell. In CIO4solutions, U022+ is hydrated by a maximum of four water molecules and complex formation is negligible. Bidentate complexing occurs with N03and the equilibrium quotient for the formation of the mononitrato complex is roughly an order of magnitude greater than that for the dinitrato complex. Complexing is evident in the Cland Brsolutions but spectral complexities prevented an unambiguous identification of the species.