How can the rotary power of a molecule be determined by comparing substructures?

[louie3006]

how can i tell if a molecule is dextorotory or levorotory by looking at the 3-d presentation? any thoughts!

 

[blitz.km]

No, we can not judge this just looking at the 3-d presentation of a compound.
It is judged by experimentation.

We pass plane-polarized light through the compound..
if the compound rotates the light clockwise, it is said to be dextro-rotatory..
and if the compound rotates the light anti-clockwise, it is said to be levo-rotatory.

 

[chemisttree]

There is some work in that field. I remember something about the requirement to compare a part or sub structure's rotary power of a larger molecule and apply the result across the entire molecule. References within http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6THT-4CPD575-3&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1066511998&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=7b2dce750534a20105a5a375820dfe5c" (specifically, J. Org. Chem. 2003, 68, 5186) should describe one group's efforts along those lines. If you are close to a library, you might look it up.