A Study of 13C Chemical Shifts for a Series of 2-(4-methoxyphenyl)-substituted-3-phenyl-1,3-thiazolidin-4-ones

Abstract

The <sup>13</sup>C substituent chemical shifts C-2, C-4 and C-5 (with a particular focus at C-2) for disubstituted 2,3-diphenylthiazolidin-4-ones with one substituent in each phenyl ring are systematically being investigated. The substituents in question are <em>p</em>-NO<sub>2</sub>, <em>m</em>-NO<sub>2</sub>, <em>p</em>-F, <em>m</em>-F, <em>p</em>-Cl, <em>m</em>-Cl, <em>p</em>-Br, <em>m</em>-Br, H, <em>p</em>-CH<sub>3</sub>, <em>m</em>-CH<sub>3</sub>, <em>p</em>-OCH<sub>3</sub> and <em>m</em>-OCH<sub>3</sub>. This combination of substituents leads to a 13 x 13 matrix array of compounds with the fixed substituents in the 2-phenyl ring constituting the columns and the fixed substituents in the 3-phenyl rings constituting the rows. Including this present study, 81 of the total 169 compounds in the matrix have been analyzed. A single <em>para</em>-methoxy group interacting with another fixed substituent, as measured by <sup>13</sup>C substituent chemical shift values at C-2 in either the C-2 phenyl or N-3 phenyl rings, shows little deviation. This changes however when the moiety is either an alkyl group at N-3 or when a <em>para</em>-methoxy group is the fixed substituent on the N-3 phenyl ring. This present study shows that a <em>para</em>-methoxy group on a C-2 phenyl ring shows a similar deviation in the efficacy in the transmission of electronic effects witnessed in this set of matrix compounds and mimics the issues seen with a previously studied <em>para</em>-methoxy substituted system with the <em>para</em>-methoxy group on the N-3 phenyl ring. Reasons for these aberrations are discussed.