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UW-Madison CHEM 345 - The Crystal Structure of the Ethyl Grignard Reagent, Ethylmagnesium Bromide Dietherate

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Other features of the spectra for this radical agree with this interpretation. The quintet structure that appears when the field is oriented perpendicular to the radical plane suggests that the 14N and the amino group hydrogens couple equally with the electron. When the magnetic field is directed along the a axis a group of well-resolved doublets appears in the hyperfine pattern. For this same orientation the doublet structure collapses to the basic seven-line pattern when deuterium replaces hydrogen on the amino group. The maximum doublet splitting attributed to an amino group hydrogen appears in the orientation very near the direction of the max- imum value for the methyl group coupling. The maximum coupling of the methyl groups is predicted’ to occur when the field is in the radical plane and perpendicular to the C(a)-CONH2 bond. Theory predicts and observations confirm lo that the maximum 5375 coupling for hydrogen bonded to nitrogen in a nitrogen- centered T radical occurs when the field is in the nodal plane of the nitrogen p orbital and perpendicular to the N-H bond. The minimum coupling for such hydrogen occurs when the field is parallel to the N-H bond, The qualitative features of the spectra associated with the amino group protons for each of the radicals studied agree with these predictions. It is possible that the doublet structure from the amino group proton arises from electron spin density on oxygen with coupling through the hydrogen bond network. This would require an unreasonably large spin density on oxygen to explain the magnitude of the splitting observed (3.1 G in the case of radical 1). We wish to thank Dr. H. Wallace Baird for his assistance with the X-ray diffraction results. Acknowledgment. The Crystal Structure of the Ethyl Grignard Reagent, Ethylmagnesium Bromide Dietheratel L. J. Guggenberger2* and R. E. Rundle2b Contribution from the Institute for Atomic Research and the Department of Chemistry, Iowa State University, Ames, Iowa 50010. Received March 1, 1968 Abstract: An X-ray diffraction study of the ethyl Grignard reagent in diethyl ether was undertaken to establish the structure of this reagent in the solid state. Crystals of C2HsMgBr.2(CzHs)z0 are mordoclinic with space group P2& and four formula units per cell of dimensions a = 13.18 A, b = 10.27 A, c = 11.42 A, and /3 = 103.3”. The structure consists of the packing of discrete monomer units with a bromine atom, an ethyl group, and two ether groups tetrahedrally coordinated to a magnesium atom. nvestigations into the nature of the Grignard reagent I have been numerous and diverse in the recent lit- erature. This problem is discussed in two recent re- view~~,~ which testify to the scope of the research done and the problems involved in its interpreta- tion. The purpose of this paper is to present and dis- cuss the details of the crystal structure refinement of the ethyl Grignard reagent. A preliminary account of this work was reported earlier.5 Experimental Section The ethyl Grignard solution was prepared in the conventional way in diethyl ether in about 1 Mconcentration. The details of the solution preparation, purification, and transfer into glass capillaries will ,not be given here since they are similar to those reported by Stucky in his work6 on the phenyl Grignard reagent. Single crys- tals were grown in Lindemann glass capillaries by cooling with a (1) Contribution No. 2271 ; work was performed in the Ames Labora- (2) (a) Central Research Department, E. I. du Pont de Nemours and (3) B. J. Wakefield, Organometal. Chem. Rev., 1, 131 (1966). (4) E. C. Ashby, Quart. Reu. (London), 21, 259 (1967). (5) L. J. Guggenberger and R. E. Rundle, J. Am. Chem. Soc., 86, tory of the U. S. Atomic Energy Commission. Co., Wilmington, Del. (b) Deceased, Oct 9, 1963. 5344 (1964). (6) ’G. Sfucky and R. E. Rundle, ibid., 86,4825 (1964); G. Stucky and R. E. Rundle, ibid., 85, 1002 (1963). cold nitrogen gas stream. Crystals during growth were consistently prismatic with monoclinic G, point symmetry. No effort was made to determine the crystal melting point accurately, but it is estimated to be about 15”. Ethylmagnesium bromide dietherate crystallizes in the mono- clinic system with cell parameters of a = 13.18 i 0.03, b = 10.27 i 0.03, c = 11.42 * 0.03 A, and 0 = 103.3 & 0.3”. The calcu- lated density on the basis of four formula units per cell is 1.24 g/cm3. It was not possible to obtain an experimental density. The systematic absences of { MI), I = 2n + 1, and { OkO), k = 2n + 1, establish the space group as P2Jc. All atoms in the cell are in the general positions? i(x, y, z; x, The following nine zones of intensity data were measured on the precession camera on two crystals using Zr-filtered Mo Ka radia- tion: (OkI), {MI], and { 2kl] on the first crystal and { hOI], { hll), (h2/), (hkO], (hkl], and (hk2) on the second crystal. The data were measured at about -75”. The entire camera was enclosed in a polyethylene tent as this proved to be the only effective way of preventing icing of the capillary. Crystals used were cylindrical in shape with diameter and length of about 0.3 mm. Timed exposures were taken according to urn with a = 1 min, r = 2, and n = 0, 1, . . ., 8. The intensities were measured by comparison with a series of standard intensities. On those photo- graphs showing mm symmetry, two quadrants were judged and then averaged. A total of 979 observed reflections was judged. The errors in the structure factors were assigned using a modified Hughes schemes so that - y, + z). (7) “International Tables for X-Ray Crystallography,” Vol. I, The (8) “International Tables for X-Ray Crystallography,” Vol. 11, Kynoch Press, Birmingham, England, 1952, p 99. The Kynoch Press, Birmingham, England, 1959, p 328. Guggenberger, Rundle Ethylmagnesium Bromide Dietherate5376 Table I. Final Atomic Parameters (X lo4) with Standard Deviations0 Br 1413 (2) -0212 (3) 2113 (2) 67 (1) 106 (3) 94(2) -5 (3) 19 (1) 9 (4) Mg 2762 (4) 0185 (8) 0962 (5) 61 (4) 82(7) 81 (5) 5 (7) 9 (4) 9 (9) O(1) 2247 (14) 1824 (14) 0023 (15) 71 (12) 67 (15) 126 (20) -23 (13) 38 (14) 21 (18) O(2) 2453 (12) -1195


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UW-Madison CHEM 345 - The Crystal Structure of the Ethyl Grignard Reagent, Ethylmagnesium Bromide Dietherate

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