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8460717 
Journal Article 
Nature of 3d Orbitals in Ylides. Experimental and Theoretical Studies of the Ultraviolet Spectra of Cyclopentadienylides 
Iwata, K; Yoneda, S; Yoshida, ZI 
1971 
Yes 
Journal of the American Chemical Society
ISSN: 0002-7863
EISSN: 1520-5126 
93 
25 
6745-6750 
English 
Two stable ylides, dimethylsulfonium cyclopentadienylide (I) and tri-n-propylphosphonium cyclopentadienylide(II), are synthesized, and their uv spectra are measured in several solvents. The spectrum measured in n-hexane consists of three bands, A, B, and C. When the solvent is changed from n-hexane to methanol, a large blue shift is observed on the longest wavelength band, A. A semiempirical MO calculation (the “method of composite molecule”) for I and II has shown that the uv spectra of I and II can be satisfactorily explained by the 3d orbital of free sulfur or phosphorus (i.e., by the Slater 3d orbital with effective nuclear charge Z3d ≈ 1.4). The A band is assigned to the transition from the ground state of the ylide to that of the ylene (i.e., an intramolecular electron-transfer-band), the B band to E2' (D5h) of the cyclopentadienyl anion, and the C band to E1' (D5h) of the cyclopentadienyl anion. The pπ-dπ resonance (ylide-ylene resonance) energies in the ground states are 32 kcal/mol for I and 31 kcal/mol for II, and the amounts of ylide structure in the ground state are 83 % for I and 84 % for II. The effect of molecular fields on 3d orbitals is also discussed. © 1971, American Chemical Society. All rights reserved.