[kind heart]

hi
please i want solution for this qusition
1-   The A llene derivatives and Biphyny Derivatives do not posses an asymmetric carbon atom and still they exhibit optical activity . Discuss.

[fledarmus]

Sit down with some molecular models, make some biphenyls and allenes, and consider the problem.

[spirochete]

One way to describe the criteria for optical activity:  a molecule is optically active if it has a non super-imposable mirror image.

In the case of biphenyls you also have to consider the fact that many biphenyls have unusually high barriers for rotation around the central bond connecting the two aryl components.  Note that not all biphenyl compounds are optically active:  there must be restricted rotation around bond connecting the two aryl rings, and also they must have a special kind of substitution.

[fledarmus]

There is a brief description of this property here, with links that might help you expand it...

http://en.wikipedia.org/wiki/Axial_chirality

[discodermolide]

Here is an X-ray of a binaphthyl analogue, which is chiral!
I hope it helps as you can see the top rings cannot rotate around the bottom ones.