propyl carbinol, there might also be a hydride transfer competing with hydroxide transfer. In the rhodium chloride-catalyzed rearrangement of cyclopropyl carbinol, some of the products have an isobutyl or isobutylene structure. Isobutylene, propane, and propylene form. Other gaseous products are n-butenes and 1,3-butadiene. Rearrangement products found in the volatile liquid fraction from the cyclopropyl carbinol reactions include isobutyraldehyde and methacrolein. Also, the straight-chain C 4 aldehydes, butyraldehyde and crotonaldehyde, have been found. In explaining the formation of some of these products, Dr. Rinehart and Dr. Fuest say that rupture of the cyclopropyl bond can occur at the allylic position accompanied by a hydride shift. This produces a pi-allyl complex from which straight-chain C 4 aldehydes and hydrocarbons form. Rupture at the homoallylic position, they add, proceeds by a homo pi-allyl complex. This would produce branched-chain products. For example, isobutylene forms by homoallylic bond rupture with a hydroxide transfer, they explain. The products with branched-chain structures are in marked contrast to the rearrangement products of cyclopropylcarbinyl cation. Under carbonium ion conditions, cyclobutyl derivatives, but no isobutyl derivatives, usually form. To get more insight on the pi-allyl and homo pi-allyl mechanisms, Dr. Rinehart and Dr. Fuest are currently studying the reactions of 5-hydroxynorbornene-2 with rhodium chloride.
Liquid 0F2-Silica Mixture Explodes Spontaneous explosion can occur in a liquid OF 2 -silica gel mixture under certain conditions, according to Dr. Florence I. Metz and her co-workers at Midwest Research Institute (Kansas City, Mo.). During the course of electron paramagnetic resonance studies of liquid OF 2 , the MRI scientists found that a mixture of 6 0 / 8 0 mesh silica gel and liquid O F 2 at 254 torr in a 3- or 4-mm. (inside diameter) tube exploded when the temperature exceeded 77° K. To date, no explosion has occurred in 5-mm. tubes under identical conditions. Other tube diameters have not been tried.
Tetranitrogen Tetrasulfide Contains Some Bonding Between Sulfur Atoms Calculations indicate that the molecule has appreciable pi-electron derealization The tetranitrogen tetrasulfide (N 4 S 4 ) molecule is an eight-membered ring of alternating sulfur and nitrogen atoms with some bonding between sulfur atoms at opposite apexes (C&EN, Feb. 8, page 3 7 ) . In addition, the molecule contains considerable pi-electron derealizations—some valence electrons are not localized on any particular atom but move through the whole molecule. Dr. Almon G. Turner of Polytechnic Institute of Brooklyn has reached these conclusions from self-consistent field (SCF) molecular orbital calculations. His calculations were made excluding electron repulsions. Inorganic chemists have been interested in the geometrical and electronic structure of tetranitrogen tetrasulfide for some time, Dr. Turner told the Fourth Annual Metropolitan Regional Meeting of the ACS, held at Stevens Institute (Hoboken, N.J.). In the past, there has been some controversy over whether the four nitrogen atoms are coplanar or the four sulfur atoms are in one plane. Chemists now generally accept the geometrical structure arrived at by Dr. B. D. Sharma and Dr. Jerry Donohue at the University of Southern California, Los Angeles. From the results of a three-dimensional x-ray study, the USC pair concluded that the molecule's four nitrogen atoms lie in a plane, while the sulfur atoms lie above and below the plane. Dr. Turner's molecular orbital calculations also favor the coplanar nitrogen structure over the coplanar sulfur. Using the extended Huckel theory developed by Dr. Roald Hoffman and Dr. W. N. Lipscomb of Harvard University and the SCF method, Dr. Turner has carried out molecular orbital calculations on N 4 S 4 using several different sets of parameters and the geometrical structure of Dr. Sharma and Dr. Donohue. From his calculations, Dr. Turner views the N 4 S 4 molecule as having considerable pi-electron derealization. This arises from the overlap of 3p and 3d orbitals of the sulfur atoms with s
STRUCTURE. The geometrical structure of the tetranitrogen tetrasulfide molecule contains four coplanar nitrogen atoms, according to a three-dimensional x-ray study by Dr. B. D. Sharma and Dr. Jerry Donohue at the University of Southern California, Los Angeles. Molecular orbital calculations by Dr. Almon G. Turner of Polytechnic Institute of Brooklyn support the coplanar nitrogen structure. His calculations also indicate that there is some bonding between the sulfur atoms located on the same side of the nitrogen atom plane (shown by broken lines)
and p orbitals of the nitrogen atoms, he explains. His calculations also indicate that the nitrogen atoms are the electron-rich centers in the system and the sulfur atoms are electron deficient. His calculations show that there is some bonding between the sulfur atoms located on the same side of the plane defined by the nitrogen atoms. The bonding arises mostly by overlap of p orbitals on each of the sulfur atoms. However, about one third of the bonding comes from the participation of the d xy orbital on each sulfur. The molecule's S—S bond is about 15% as strong as its N—S bond. Thus it's considerably weaker than an S—S single bond, Dr. Turner says. Alkaline hydrolysis of tetranitrogen tetrasulfide gives dithionite, S 2 0 4 - 2 , which contains a sulfur-to-sulfur single bond, he notes. Dr. Turner's calculations give no evidence for the presence of chemical bonds between nitrogen atoms in tetranitrogen tetrasulfide. This includes nitrogen atoms located either diagonally or those bonded to the same sulfur atom. FEB.
15, 1965 C & E N
41
