Physical Properties. Structures, and Analysis

COMPARISON OF TYPICAL PHYSICOCHEMICAL PROPERTIES OF A-4-THIAZOLINE-2-THJONE (Ii WITH THOSE OF 2-(METHYLTHIO)THIAZOLE (II) AND 3-METHYL-A-4-TH1AZO-LINE-2-THIONE (UIF 

Electronic transitions of Z-methylthiothiazole and A-4-thiazoline-2-thione were calculated using Pariser-Parr-Poplc and Complete Neglect of Differential Overlap approximations (61. 72). The major improvements afforded by the CNDO model are the calculation of the n cr transition and the interpretation of the 2.34-nm band as an n transition. 

Observed and calculated bands and their location in the ring are shown in Table VIl-2. 

This band is not seen in normal ultraviolet spectra but can be measured for circular dichroism of 3-R-A-4-thiazoline-2-thione. where R possesses an asymmetric center (74). Representative ultraviolet data are also eiven in Refs. l.S and 75. 

A bathochromic shift of about 5 nm results for the 320-nm band when a methyl substituent is introduced either in the 4- or 5-posiiion, The reverse is observed when the methyl is attached to nitrogen (56). Solvent effects on this 320-nm band suggest that in the first excited state A-4-thiazoline-2-thione is less basic than in the ground state (61). Ultraviolet spectra of a large series of A-4-thiazoline-2-thiones have been reported (60. 73). 

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