This work is part of a series aimed to investigate the fundamental and overtone transitions of the CH stretching modes in partially F-substituted benzenes. In this article we report the study of the fundamental transitions of fluorobenzene (C6H5F) in the wave numbers range from about 3000 to 3150 cm(-1). The absorption spectrum has been measured through both a low-temperature opto-acoustic cell and a supersonic-beam opto-thermal spectrometer. The opto-thermal spectrometer enabled us to measure the detailed vibrational structure, providing the basis for an algebraic analysis of the fundamental CH transitions. We show, in particular, how benzene algebraic procedures must be modified for taking into account the effects induced by the substitution of one hydrogen atom with fluorine, i.e.; (i) the reduction of symmetry and (ii) the frequency (chemical) shift due to the change of electron distribution. Moreover we include the contribution of anharmonic resonances between unperturbed CH stretching modes and overtone or combination bands of lower energy molecular vibrations.