A 3,3-sigmatropic rearrangement in the M+· of phenyl allenylmethyl ether is proposed for the observed losses of CO, C2H4, and ĊH3. Direct cyclization in the M+· also leads to the [M — CH3] ion. The presence of sulfur as the heteroatom in phenyl allenylmethyl sulfide does not significantly influence the occurrence of Claisen rearrangement. Ortho interaction of the nitro group with the allenyl double bond in the side chain leads to characteristic fragment ions in 2-nitrophenyl allenylmethyl ether. Linked scans, high-resolution mass spectrometry, collision-activated dissociation—B/E linked-scan spectra, and D-labeling have been employed to support the proposed mechanisms and ion structures. © 1995, American Society for Mass Spectrometry. All rights reserved.