Auwers-Skita rule

Based on these generalizations is the Auwers-Skita rule according to which in a pair of cis-trans isomers, the cis has a higher boiling point, density and refractive index. Thus in general the trans form usually the stabler of the two isomers. 

More general statements about catalytic hydrogenation are difficult to make since the results are affected by many factors such as the catalyst, its supports, its activators or inhibitors, solvents [27], pH of the medium [27] (Auwers-Skita rule acidic medium favors cis products neutral or alkaline medium favors Irons products [22]) and to a certain extent temperature and pressure [5]. 

Other applications of the Auwers-Skita rule are also cited in Ref. 18 and Ref. 19 (Ref. 19 were located by keyword Skita). 

A modification of the Auwers-Skita rule for predicting stereochemistry of catalytic hydrogenations has been proposed, with particular reference to the desorption step. It is stated that the isomer formed preferentially has the more (most) masked polar or electron-rich groups. Thus the Auwers-Skita rule predicts formation of trans-ketone (595) from catalytic hydrogenation of (594) i ia purported delivery of hydrogen trans-to angular methyl, whereas in experiment the more compact isomer (596) was formed... 

---