In this paper, we study the effect of a porous adsorbent, such as silica with a pore diameter of 375 A on the molecular dynamics and the solid-solid phase transformations of tert-butyl chloride (t-BC) inside the pores by means of chlorine nuclear quadrupole resonance (NQR). The spin-lattice relaxation time (T-1) and the resonance frequency (v(Q)) as a function of temperature for t-BC, both in bulk and confined in the silica mesopores, have been measured. Changes are observed in the molecular dynamics and in the phase transition temperatures of the t-BC confined in the pores with respect to those corresponding to the t-BC in bulk. Likewise, phase transformation kinetics would seem to be altered due to restrictions of the molecular movement as a consequence of the confinement inside the porous material. (c) 2005 Published by Elsevier B.V.