The photochemistry of a series of acyclic, aliphatic γ,δ-unsaturated ketones in pentane solution with 185-nm light has been investigated. The variety of products formed can be rationalized as arising from discrete reactions of the individually excited chromophores. Neither intramolecular energy transfer nor internal conversion leading to population of the lowest (n,π*) singlet state are competitive with product formation at 185 nm. The mechanism of alkyne formation in the solution-phase photolysis of these and terminal alkenes at 185 nm is elucidated by using a deuterated derivative, and the reaction is postulated to proceed from the olefinic π,π singlet state. © 1982, American Chemical Society. All rights reserved.