What does dextrorotary mean?
Dextrorotary is an adjective used almost exclusively in chemistry and physics to describe a substance that rotates the plane of plane-polarized light to the right — that is, clockwise when viewed by an observer facing the incoming beam. Certain molecules, notably sugars such as glucose and sucrose, exist in chiral forms that interact with polarized light this way, and measuring the degree and direction of rotation with a polarimeter is a standard technique for identifying and assaying them. Its counterpart is 'levorotary', describing rotation to the left. The term derives from Latin 'dexter', meaning right or right-hand, which also gives English words like dexterity. In practice, writers often use the variant form 'dextrorotatory', and both are abbreviated with a plus sign (+) in chemical notation. While precise, the direction of optical rotation cannot by itself predict other properties of a molecule, so the word carries strictly descriptive, technical connotations rather than any figurative or everyday use.
adjectiveRotating or turning light to the right, or clockwise as seen by an observer facing the oncoming beam; used chiefly of optically active substances that rotate plane-polarized light in this direction.
- Of an optically active substance or solution: rotating the plane of plane-polarized light to the right, i.e. clockwise as viewed by an observer looking toward the light source.
"The sugar solution proved to be dextrorotary, bending polarized light clockwise."
"A dextrorotary solution of glucose rotates polarized light clockwise, a property exploited in polarimetry."
"Chemists labeled the two enantiomers D and L after observing which form was dextrorotary and which levorotary."
Pasteur noticed that crystals of tartaric acid came in mirror-image forms — and the dextrorotary kind was the one found in wine, a clue that helped launch stereochemistry.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of dextrorotary
Dextrorotary combines the Latin 'dexter' (right, right-hand, also skilled) with 'rotary', from Latin 'rotare', to turn or rotate. The term emerged in nineteenth-century scientific writing alongside the study of optical activity, following the discovery that quartz and various organic compounds could twist polarized light in opposite directions. It shares the 'dexter-' root with cognates such as dexterity, dextral, and ambidextrous, while its antonym levorotary draws on Latin 'laevus' (left).
Related word forms
How dextrorotary is actually used
A technical term confined mainly to chemistry and optics, particularly discussions of optical activity and enantiomers. The variant spelling 'dextrorotatory' is at least as common in scientific literature. It describes the physical behavior of a substance, not its molecular structure — the D/L and R/S descriptors are related but distinct conventions.
Easily confused with dextrorotary
Levorotary substances rotate plane-polarized light to the left (counterclockwise), whereas dextrorotary ones rotate it to the right.
Dextrorotatory is simply the more common variant spelling of the same word, not a different term.