The present invention provides monofluoroalkyl derivatives of the formula (I) wherein: A represents SO2, CO2 or CONH; Ra represents (1-6C)alkyl, (2-6C)alkenyl, -(1-4C)alkyl(3-8C)cycloalkyl, or (1-4C)alkylaromatic; Rb represents H, (1-6C)alkyl, (2-6C)alkenyl, -(1-4C)alkyl(3-8C)cycloalkyl, or (1-4C)alkylaromatic; or R?a and Rb¿ together with the carbon atoms to which they are attached form a (3-8C) saturated carbocyclic ring, a (3-8C) saturated carbocyclic ring containing a heteroatom selected from the group consisting of sulfur or oxygen, or a (5-8C) carbocyclic ring containing one double bond; R1 represents an unsubstituted or substituted aromatic group, an unsubstituted or substituted heteroaromatic group, or an unsubstituted or substituted (5-8C)cycloalkyl group; R2 represents (1-6C)alkyl, (3-6C)cycloalkyl, (1-6C)fluoroalkyl, (1-6C)chloroalkyl, (2-6C)alkenyl, (1-4C)alkoxy(1-4C)alkyl, phenyl which is unsubstituted or substituted by halogen, (1-4C)alkyl or (1-4C)alkoxy, or when A represents SO¿2?, a group of formula R?3R4¿N in which R?3 and R4¿ each independently represents (1-4C)alkyl or , together with the nitrogen atom to which they are attached form an azetidinyl, pyrrolidinyl, piperidinyl, morpholino, piperazinyl, hexahydroazepinyl or octahydroazocinyl group; or a pharmaceutically acceptable salt thereof, useful for potentiating glutamate receptor function in a mammal and thereof, useful for treating a wide variety of condutions, such as psychiatric and neurological disorder.