This Sonata D major is flanked by two others in the same key, the K. 490 and 492, that Scarlatti almost certainly wrote in the same brief time span. All were preserved, along with 27 other sonatas, in the 12th Venice volume of the composer's works, dated 1756. While they may not have been written that year, they likely date to not more than a year or two earlier.

The Sonata, K. 491, here is marked Allegro and has a slightly unusual structure for a Scarlatti sonata: the composer presents his main thematic wares, pauses, then moves onto the secondary material, almost as if it is a wholly new thematic group or a development section. Of course, as was his pattern, Scarlatti presents the expository material a second time before moving on to the actual development section, which is also given twice. The Sonata opens with an ebullient theme that springs from a three-note morsel and goes on to spawn rich contrapuntal activity. The second half of the exposition expands on the material from the opening and already goes in new directions. In the development section the themes are transformed only slightly, while maintaining their chipper, colorful character.

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