Ionization and fragmentation were studied on alkylphenols with long alkyl chains (p-(C6H4)(OH)(CnH2n+1). n = 1,3,5,8,9) and, for reference, on alkylbenzenes ((C6H5)(CnH2n+1), n = 1,3,5,7,9) by intense femtosecond laser pulses, typically with 43 fs duration at 0.8 mu m and 140 fs at 1.3 mu m in an intensity range of 10(14) W cm(-2). The major products were the corresponding molecular and C-7 fragment ions from the alkylphenols and alkylbenzenes. The molecular ion yields decreased from nearly 1 (n = 1) to 0.3-0.5 (n = 9) when the carbon number in the alkyl chain increased for both excitation wavelengths. Higher yields of the molecular ions were observed at a longer wavelength of 1.3 mu m. The long wavelengths in the range of 1.3-1.5 mu m were used to determine whether or not -OH absorption had any increase in fragment ions. No effect was observed by vibrational overtone excitation of the -OH group in this wavelength range. Direct dissociation by cation absorption is the most plausible explanation of the present fragmentation results. Other possible mechanisms were discussed, including a statistical model, an effect of electron rescattering, it multiactive electron model, and dissociation from the superexcited state In the case of cyclohexane, nonresonant wavelength excitation with a pulse of 1.3 mu m (150 fs) effectively suppressed fragmentation more than excitation by a resonant but short-duration pulse (0.8 mu m, 15 fs).