What is a gaseous hydrocarbon, C3H6, isomeric with propylene and obtained from it indirectly. It is the base of a series of compounds analogous to the aromatic hydrocarbons called?

trimethylene — A gaseous hydrocarbon, C3H6, isomeric with propylene and obtained from it indirectly. It is the base of a series of compounds analogous to the aromatic hydrocarbons. (Webster's 1913.)

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