The electronic structure of aryl thiol esters

✍ Scribed by J.R. Grunwell; S.I. Hanhan

• Publisher: Elsevier Science
• Year: 1973
• Tongue: French
• Weight: 473 KB
• Volume: 29
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(01)83386-x

✦ Synopsis

A combination of experimental data and the CNDO/Z-SCF-MO method are used to evaluate the importance of d-orbitals to the electronic structure of aryl thiol esters. The thioester group IS calculated to withdraw electron density through o and 2p,, -3d, bonding and donate by p,, -pm bonding. Electron donating substituents para to the thiol ester group cause the latter group to accept electron density regardless of d-orbital participation Three types of experimental data have beenrationalized in terms of the participation of nominally empty 3d-orbitals in the electronic structure of aryl thiol esters. First, Cilento' and later Baliah and Ganapathy2

proposed that 3d-orbitals are important in the excited states of 4-substituted phenyl thiol acetates in order to explain the bathochromic shift of the ultraviolet spectrum caused by the introduction of electron donating groups para to the thiol ester group. Second, Baliah and coworkers showed that the dipole moment for 4-N,Ndimethylaminophenyl thiol acetate is larger than the moment estimated from the moments for phenyl thiol acetate and N,N-dimethylaniline.

These data have been cited as proof that electron density is transmitted from the electron donating group to the sulfur and oxygen atoms of the thiol ester via 2p, -34 bonding between sulfur and the adjacent C atoms, an effect, which has been represented by the charge separated valence bond structures 1 and 2.