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SCIENCE PROGRESS 



a) 



(2) 





(3) 



(4) 



(5) 



(8) 



[N.B. — The numbering of the carbons is the same in all cases.] 

 It is easy to see that in this case there is no truly asymmetric 

 carbon at all ; but in each of the configurations all the carbons 

 are pseudo-asymmetric. In some cases, we find one carbon 

 neutralising the pseudo-asymmetry of another, e.g. carbons 3 

 and 5 in configuration No. 3. 



In configuration No. 1 all the carbons are pseudo-asymmetric 

 in the same sense, there being no meso-pair at all. The molecule 

 as a whole is symmetric and identical with its mirror-image. In 

 Nos. 2-7, also, we find the structures symmetric. 



