The photochemical properties of chiral molecules differ from achiral molecules primarily due to their distinct interactions with polarized light. Chiral molecules can exist as two non-superimposable mirror images, known as enantiomers. These enantiomers can rotate plane-polarized light in opposite directions, either clockwise dextrorotatory or counterclockwise levorotatory . This phenomenon is called optical activity. Achiral molecules, on the other hand, do not exhibit optical activity as they do not have enantiomers.An example of a chiral molecule is limonene, a compound found in citrus fruits. Limonene has two enantiomers: R-limonene, which has a pleasant orange scent, and S-limonene, which has a lemon scent. The molecular structure of these enantiomers is identical, except for the arrangement of atoms in three-dimensional space.Light absorption can affect the molecular structure and biological activity of chiral molecules through a process called photoisomerization. When a chiral molecule absorbs light, it can undergo a structural change, such as a rotation around a single bond or an inversion of a stereocenter, which can lead to the formation of its enantiomer or another stereoisomer. This change in molecular structure can significantly impact the molecule's biological activity, as the interactions between the molecule and its biological target e.g., a protein or receptor are often highly stereospecific.For example, in the case of limonene, exposure to ultraviolet UV light can cause photoisomerization, leading to a change in the molecule's chiral center and potentially converting R-limonene to S-limonene or vice versa. This change in molecular structure can alter the scent of the compound, as well as its interactions with olfactory receptors, which are responsible for detecting and differentiating between different smells.In summary, the photochemical properties of chiral molecules differ from achiral molecules due to their unique interactions with polarized light and their ability to undergo photoisomerization, which can significantly impact their molecular structure and biological activity.