What is a colorless, volatile, pungent liquid, C4H6, produced artificially, and regarded as an unsaturated hydrocarbon of the acetylene series, and analogous to crotonic acid called?

crotonylene — A colorless, volatile, pungent liquid, C4H6, produced artificially, and regarded as an unsaturated hydrocarbon of the acetylene series, and analogous to crotonic acid. (Webster's 1913.)

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