The Crystal and Molecular Structure of 1‐Methyl‐1‐Thionia‐Cyclohexane Iodide

Abstract

Summary. Crystals of 1-methyl-1-thionia-cyclohexane iodide are orthorhombic with space group PnaZ1, a = 18.036, b = 6.611, c = 7.420 k, 2 = 4. The crystal structure was solved by the heavy-atom method. Very strong parameter interactions prevented least-squares refinement of atoms other than S and I. The molecule adopts the chair conformation with the methyl group in equatorial position.Saturated ring systems containing one or several sulfur atoms have been less studied than those containing elements of the second period, though theoretically interesting conformational features might be associated with the different oxidation states of sulfur. Several cases are known where a bulky exocyclic group attached to an heterosulfur atom prefers to adopt an axial position [l]. The question might arise as to the orientation of a group attached to formally positive sulfur, as in cyclic sulfoniums. We now report the structure of 1-methyl-thionia-cyclohexane iodide (1) as determined by X-ray analysis. systematic extinctions is consistent with the space groups Pna2, and Pnam (Pnma, with the appropriate axis setting). At a later stage of the investigation, Pna2, proved to be correct. The crystalline compound 1 is very prone to decomposition under X-ray irradiation, and four crystals were necessary to collect the 1280 reflections used in this determination. Intensity data were measured on a Hilger & Watts Y190 linear diffractometer by the moving crystal-stationary counter method, with balanced filter and Mo radiation, a t an w-scan standard time of 140 sec. The main set of 1060 reflections was collected by rotating the crystal about the c axis; the correlation factors to bring reflections of various layers to a common intensity scale were calculated by a leastsquares procedure including reflections collected from a crystal rotated about the b axis. No corrections were made for absorption.Structure Analysis and Refinement. -The heavy-atom method was used for the determination of the atomic positions of the iodine and sulfur atoms from a three-dimensional Patterson synthesis. The number of molecules in the unit cell suggests space group PnaZl rather than Pnma, unless m is also a mirror plane for the ion-pair C,H13S+I-; the latter possibility entails relationships among the variables of the Harker lines. The relationships were absent in the Patterson synthesis, which, on the PnaZl assumption, allowed straightforward determination of the coordinates of the I and S atoms (21 was arbitrarily fixed at zero). Two-and then three-dimensional Fourier syn-

More space-group changes

“…The structure of this compound was described (Gerdil, 1974) No coordinate needs to be shifted by more than 0.05 A to attain the symmetry of Pnam, and while we were unable to obtain a listing of F values, we have no doubt that the Pnam description is preferable. The Pnam coordinates (averaged where necessary) are given in Table 18.…”

“…The Pnam coordinates (averaged where necessary) are given in Table 18. Gerdil (1974) noted that the derived structure was unreliable because of ill conditioning of the leastsquares matrix. This ill conditioning surely arose from attempts to refine a closely centrosymmetric structure in a non-centrosymmetric space group, and would disappear in Pnam.…”

Hydrogen‐Bonding Catalysis of Alkyl‐Onium Salts

“…To create new possibilities for trialkylsulfonium salts, our group also became interested in the hydrogen‐bonding catalysis of cyclic trialkylsulfonium salts 9 when we determined that cyclic tetraalkylammonium salts 1 worked as hydrogen‐bonding catalysts on the basis of the characteristic properties of the α‐hydrogen atoms (Figure , see also Schemes and ) . The structure and anion binding mode of sulfonium iodide 9 a is similar to that of ammonium iodide 1 a . Additionally, the acidity of the α‐hydrogen atoms of 9 a is expected to approximate the acidity of 1 a , based on the reported p K a values …”

Hydrogen-Bonding Catalysis with Sulfonium Salts

“…The structures of the α hydrogen atoms that binded to the iodide anion compared favorably to the X-ray crystal structures of ammonium iodide 1a and sulfonium iodide 2a. 9,10 Furthermore, we expected the acidity of the α hydrogen atoms of 2a to approximate the acidity of 1a, based on the reported pKa values. 11…”