[wacki]

Are alkenes optically active stereo centers?   

I did some googling and question 15.38 at this PDF talks about even and odd:
http://voh.chem.ucla.edu/vohtar/spring03/classes/30C/pdf/30cps1ky.pdf

It says odd # of double bonds are in the same plane and are NOT chiral.  So are even double bonds optically active?

[curiouscat]

Cumulated double bonds.

[fledarmus]

Are alkenes optically active stereo centers?   

It says odd # of double bonds are in the same plane and are NOT chiral. 

So no, alkenes (1 double bond) are not active because the substituents are planar, and thus alkenes always have a mirror plane (the plane of the double bond). Allenes (2 double bonds sharing a single carbon atom) can be chiral with the right substituents, because the substituents are at 90° to each other. As more double bonds get linked to the ends to form the various cumulenes, the ones with even numbers of double bonds can be chiral, the ones with odd numbered double bonds are not chiral.

[wacki]

Wow, thank you guys for the great answers.

I view the situation as:
Alkenes = cis / trans but not R/S.  no optical activity
Allenes = no cis / trans properties due to 90 degree angle but they can have R/S as well as optical activity

Is that correct?

Also, I assume that allenes and alkenes should be treated the same for the 2^n isomers rule.   One simply has R/S while the other is cis/trans.  Correct?