Steric Hindrance in Strongly Polar 2,6‐Disubstituted Azobenzenes

Abstract

The (tritylthi0)azetidinones (2) react with mercury([[) acetate or (methoxycarbony1)mercury acetate in methanol at room temperature to give good yields of the (mercurithi0)azetidinones of type (3) or ( 4 ) , respectively. These relatively apolar compounds can be purified without decomposition by chromatography on silica gel. The products (3) and ( 4 ) react instantaneously with hydrogen sulfide in an inert solvent, even in the cold, with deposition of mercury sulfide and quantitative formation of the relatively stable 4-mercapto-2-azetidinones ( 5 ) .

Colour fastness properties of alkali‐clearable azo disperse dyes containing a fluoro‐sulphonyl group

“…In the 2′-nitro derivatives a coplanar configuration is not possible, however, and steric interactions are minimised by the possibility of the nitro group rotating outside the molecular plane. This explains the decreased bathochromic effect of 2′-nitro compared with 4′-nitro substituents [24]. The partially delocalised configuration giving higher electron density on the azo nitrogen atoms of the 2′-nitro derivative, confirmed by mass spectra fragmentation data [20], results in lower light fastness.…”

Structure—wet fastness relationships of some blue disperse dyes for polyester

“…Although the nitro function is a stronger electron acceptor than the cyano group, it is generally true that 2,6dicyano-substituted azo dyes are bathochromic, and thus give greener hues, relative to 2-bromo-6-nitro and 2,6dinitro analogues, since there is less steric hindrance of the azo link associated with this substitution pattern [16]. Both the observed absorption maxima of dyes 4 and their polyester dyeings are consistent with this pattern: the order of bathochromism in DMF is 4c > 4a > 4b, while the dicyano derivative 4c conferred the greenest shade in the series.…”