Structure

The prefix "levo-" refers to the shape of the molecule. Below is a diagram of the compound. 

The molecule itself is actually called thyroxine, but the "levo-" tells chemists the shape of the compound.

Percent Composition (by mass):

C  22.55%
 H 1.26%
 I 63.54%
 N 1.75%
 Na 2.88%
 O 8.01%

Percent Composition (by number): 

C 42.86%
 H 28.57%
 I 11.43%
 N 3.13%
 Na 3.13%
 O 11.43%

Peak Plasma level: 2-4 hours

Plasma half life: 7 days