An organic molecule necessarily shows optical activity if it
Answers
and absolute configuration.
A molecule with a single stereocenter such as limonene and carvone have two stereoisomers, one rotates polarized light to the left (-) and the other to the right (+). Additionally, each one has its own absolute configuration in their chiral center, which can be R or S. The thing is, R and S configurations are not attached or are, anyhow, synonyms with (+) and (-) configurations. Carvone and Limonene are good examples:
Carvone
Limonene
In carvone, the S enantiomer rotates polarized light to the left and so it is named S-(+)-Carvone. The S enantiomer in limonene rotates polarized light to the right and so it is named S-(-)-Limonene. The two nomenclature systems are different since they specify distinct properties.
I hope this answers your question. If not, I would be glad to help in anyway I can.