Chiral:
In chemistry, a molecule or ion is called chiral (/kaɪˈræl/) if it cannot be superposed on its mirror image by any combination of rotations and translations. This geometric property is called chirality. The terms are derived from Ancient Greek χείρ (cheir), meaning “hand”; which is the canonical example of an object with this property. [Wikipedia]
Noted in “Life’s other mystery: Why biology’s building blocks are so lop-sided,” Hayley Bennett, NewScientist (18 April 2020, paywall):
Indeed, most complex molecules have at least two possible “mirror” versions, known as left and right-handed “enantiomers”. This matters because the alternatives can have remarkably different properties or effects. The two opposite-handed versions of the chemical known as carvone, for instance, give the spearmint and caraway plants their distinctive aromas. Similarly, the enantiomers of limonene, both formed naturally, smell differently: one of lemon, the other of orange.
The phenomenon has implications in drug development too. In the pharmaceutical industry, enantiomers often have to be painstakingly separated because one version of a drug doesn’t work or isn’t safe. Thalidomide, for example, was a right-handed molecule that caused birth deformities in thousands of babies, whereas its left-handed form safely treats pregnancy sickness.
