gogo - 5-12-2008 at 00:44
HELP!!!
in mannich or aldol reaction, syn or anti were used to describe the relative configuration of adjacent groups. however, when cyclic compounds were
used, how to use these words to describe the relative conformation? for instance, i will give my problem as following:
The absolute configuration for both of the chiral centers are "S,S", as to the rigid conformation of the cyclic five-member ring, how to describe the
relative configuration of the two asymmetric carbon? is it syn- or anti-? and please give some references.
THANK YOU SO MUCH!!
[Edited on 5-12-2008 by gogo]
Nicodem - 5-12-2008 at 01:13
Syn- and anti- are referred to the orientation of two substituents in rotamers. Since you can not have rotamers in a cyclic system,
you better use the trans- and cis- descriptors for explaining the relative orientation of two substituents in a diastereomeric
relation. But that can generally only be done for explaining the relation of two substituents. If you need to name the compounds you need to
use the E and Z descriptors for diastereomers or absolute stereochemical descriptors for enantiomers (though for diastereomers
having at least two identical substituents you can use the trans/cis for naming the compound since it then becomes unambiguous).