The IR spectra of 1-pentene, 2-methyl-1-butene, 2-methyl-2-butene and isoprene (2-methyl-1,3-butadiene) liquid and adsorbed on NaX zeolite have been recorded. Empirical assignments for the observed spectrum (4000-1200 cm(-1)) are reported in all cases. Data on the adsorption of water, acetonitrile and C5 alkanes on NaX are also briefly discussed. The behaviour of NaX zeolite in the separation of alkenes from alkanes in selective adsorption processes is also briefly discussed. (C) 1999 Elsevier Science B.V. All rights reserved.