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The Tolman electronic parameter (TEP), named after Chadwick A. Tolman, is a measure of the electron donating or withdrawing ability of a ligand. It is determined by measuring the frequency of the A1 C-O vibrational mode of a complex, LNi(CO)3 by infrared spectroscopy, where L is the ligand being studied. LNi(CO)3 was chosen as the model compound because such complexes are readily prepared from tetracarbonylnickel(0). :350px The carbonyl band is quite distinctive, and is rarely obscured by other bands in the analyte's infrared spectrum. Carbonyl is a small ligand so steric factors do not complicate the analysis. Upon coordination to a metal, ν(CO) typically decreases from 2143 cm−1 of free CO. This can be explained by π backbonding: the metal is able to form a π bond with the carbonyl ligand by donating electrons through its d orbitals into the empty π * anti-bonding orbitals on CO. This strengthens the metal-carbon bond, but also weakens the carbon-oxygen bond. If other ligands increase the density of π electrons on the metal, the C-O bond is weakened and ν(CO) decreases; conversely, if other ligands compete with CO for π backbonding, ν(CO) increases. The Tolman cone angle and TEP has been used to characterize the steric and electronic properties of phosphines, which are popular ligands for catalysts. ==See also== * Metal carbonyl 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tolman electronic parameter」の詳細全文を読む スポンサード リンク
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