Formation of p-cymene from OH + γ-terpinene: H-atom abstraction from the cyclohexadiene ring structure

γ-Terpinene [1-methyl-4-(1-methylethyl)-1,4-cyclohexadiene] is a C10 monoterpene emitted in relatively small amounts from vegetation. p-Cymene [1-methyl-4-(1-methylethyl)benzene or 4-isopropyltoluene] is formed from the OH + γ-terpinene reaction after H-atom abstraction from the two ring CH2 groups, and its molar formation yield has been measured to be 13.6 ± 2.5%. This corresponds to a rate constant for H-atom abstraction from the ring CH2 groups in γ-terpinene of (2.41 ± 0.45) × 10−11 cm3 molecule−1 s−1, a factor of ∼1.7 higher than the literature rate constants for the corresponding H-atom abstraction pathways in the OH radical-initiated reactions of 1,3- and 1,4-cyclohexadiene but significantly lower than the reported overall H-atom abstraction rate constants in the OH + α-terpinene and α-phellandrene reactions.

► p-Cymene is formed after H-atom abstraction from the ring CH2 groups in γ-terpinene.
► p-Cymene data lead to abstraction rate constant of 2.4 × 10−11 cm3 molecule−1 s−1.
► Our rate constant is lower than those reported for α-terpinene and α-phellandrene.