![]() ![]() ![]() ![]() For sulfuric acid, computational analysis (with natural bond orbitals) confirms a clear positive charge on sulfur (theoretically +2.45) and a low 3d occupancy. However, in this description, despite there being some π character to the S−O bonds, the bond has significant ionic character. In this model, fully occupied p orbitals on oxygen overlap with empty sulfur d orbitals (principally the d z 2 and d x 2– y 2). Ī widely accepted description involving pπ – dπ bonding was initially proposed by Durward William John Cruickshank. The outcome was a broad consensus that d orbitals play a role, but are not as significant as Pauling had believed. Pauling's use of d orbitals provoked a debate on the relative importance of pi bonding and bond polarity ( electrostatic attraction) in causing the shortening of the S−O bond. The double bonding was taken by Pauling to account for the shortness of the S−O bond. The S−O bond length of 149 pm is shorter than the bond lengths in sulfuric acid of 157 pm for S−OH. His reasoning was that the charge on sulfur was thus reduced, in accordance with his principle of electroneutrality. Later, Linus Pauling used valence bond theory to propose that the most significant resonance canonicals had two pi bonds involving d orbitals. The first description of the bonding in modern terms was by Gilbert Lewis in his groundbreaking paper of 1916 where he described the bonding in terms of electron octets around each atom, that is no double bonds and a formal charge of +2 on the sulfur atom.
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