in chemistry, the spatial rearrangement of atoms or groups of atoms in a dissymmetric molecule, giving rise to a product with a molecular configuration that is a mirror image of that of the original molecule.

The reaction is usually one in which an atom or a group of atoms in the molecule is replaced by another atom or group. The phenomenon of inversion is sometimes known as Walden inversion, after the German chemist Paul Walden, who discovered it in 1895. The idea that inversion is the stereochemical consequence of a nucleophilic displacement reaction was introduced by the British chemists Sir Christopher Ingold and E.D. Hughes (see substitution reaction).

in literary style and rhetoric, the syntactic reversal of the normal order of the words and phrases in a sentence, as, in English, the placing of an adjective after the noun it modifies (“the form divine”), a verb before its subject (“Came the dawn”), or a noun preceding its preposition (“worlds between”). Inversion is most commonly used in poetry in which it may both satisfy the demands of the metre and achieve emphasis:

Inversion used simply for the sake of maintaining a rhyme scheme is considered a literary defect, although it is a common convention in folk ballads:

in music, rearrangement of the top-to-bottom elements in an interval, a chord, a melody, or a group of contrapuntal lines of music. The inversion of chords and intervals is utilized for various purposes, e.g., to create a melodic bass line or (with certain chords) to modulate to a new key. To invert a chord or an interval is to rearrange its notes so that the original bottom note becomes an upper note; for example,

An interval (such as c′–f′) and its inversion (f′–c″) are complementary: together they form an octave. A three-note chord (triad) can be inverted twice from its original, or root, position.

Inversions of melody and counterpoint enable a composer to elaborate on basic musical material; they are common in fugues. To invert a melody means to change its ascending intervals to descending ones and vice versa; for example:

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In inverted counterpoint, the original order of the contrapuntal lines is rearranged. In this way a line sounds above the line that it originally sounded beneath; for example,

becomes