formula for copper sulfide is given as C U ~ .and ~ ~ Cul.&. S The value for the most favorable range in the Bacon data is 78.0 * 0.25% copper which gives the formula for copper sulfide as about C U ~ . ~ S . Bacon assumed that these deviations from a whole number relationship were probably due to the formation of some CuS and that the experiment was probably satisfactory for the purpose intended. Dingledy and Barnard state that X-ray diffraction analysis of a copper sulfide sample containing 78.3% copper (formula C U ~ . ~is~ aS product ) of two phases: digenite (CurSs = Cul$) and chalocite (Cuss). A suitable proportion of these two phases could result in the formula, CUI.&. They also believe that the experiment is not a suitable one to demonstrate the law of constant proportion. Whatever is or may have been the objectives of these studies, the apparent fact is that student dataohtained from laboratory work is usually right.
To the Editor: Dr. Luder's paper [THISJOURNAL, 44,269 (1967)l advancing Linnett's multi-electron bond approach appears to have some significance in the general interpretation of chemical bonding. To explain the planarity of trisilylamine in the absence of resonance hybridization, Dr. Luder assumes that the unshared electrons on the nitrogen atom are separated, "one electron on one side of the plane, and the other on the opposite of the plane." The larger size of the silicon atom over carbon is held responsible as a steric reason for maximum separation of the silicon moieties. By the same reasoning, the germyl, stannyl, and plumbyl groups, significantly larger than silicon, would also be expected to assume planar skeletons. The short table below emphasizes the uniqueness of the silicon derivatives of nitrogen and phosphorus. Pyramidal Compounds of Nitrogen and Phosphorus
Planar Compounds of Nitrogen and Phosphorus
General Reference: HESTER,R., AND JONES,K., Chem. Cmrn., 317 (1966).
In the light of Randall and Zuckerman's [Chem. Comm., 733 (1966)l "agnostic view" of (u -,d)a resonance contributions in M-N bonded systems (M = Group IV metal), one hesitates to do much more than point out the inconsistent nature of the %on-closely paired" explanation in these instances. I t is thought, however, that application of multipleelectron bond designations to the complex oxides of nitrogen, phosphorus, and sulfur, to unsaturated organic
linkages, and perhaps to the boron hydride bridged species is an acceptable adjunct to resonance hybrid theory. Supplementation of the many artificially pictured, two-dimensional arrangements of electrons in atoms and atoms in molecules is thus welcomed. PAULS. POSKOZIM SAMHOUSTON STATECOLLEGE HUNTSVILLE, TEXAS77340
To the Editor: Dr. W. F. Luder in his paper about the electron repulsion theory of the chemical bond [THIS JOURNAL 44,206 (1967)l accepts for the Linnett formula of benzene the hexagonal spatial configuration proposed by Graebe [Ber. 35 526 (1902)l. I believe that is not correct. Such a configuration can contain any number of carbon atoms. Hence cyclooctatetraene can have the Linnett formula and be aromatic. This inconsistency can he avoided if we assume for Linnett benzene the Sachse model:
[Ber. 21 2530 (1888)l. I n it every carbon atom t e t r . ~ hedron shares an edge with two neighboring tetrahedra. Thus this model corresponds to a three electron bond. I t can be built only of six carbon atoms. 227 MCCARTNEY ST. Easton, Pennsylvania 18042
To the Editor: In reply to the letter by A. Sementsov, may I point out first that the Linnett formula for benzene minimizes electron repulsion not only by having no close-pairs in the ring, but also by having all bond angles exactly the correct value (120'). This condition cannot he realized with eight carbon atoms in the same plane. Consequently, cyclooctatetraene does not have 3-electron bonds and is not planar. Second, the Sachse model cannot be accepted because three of the H atoms, the six C atoms, and the other three H atoms are in three different planes, and because each group of three electrons is shared at a common coyner by three C atoms, an arrangement that produces a very high electron repulsion. W. F. LUDER NORTHEA~TERN UNIVERSITY BOBTON, ~~SS.~CHUSETTS
Volume 44, Number 10, October 1967
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