Crystal structures of three homologues with increasing ring size: 2-meth­oxy-4-(thio­phen-2-yl)-5,6,7,8-tetra­hydro­quinoline-3-carbo­nitrile, 2-meth­oxy-4-(thio­phen-2-yl)-6,7,8,9-tetra­hydro-5H-cyclo­hepta­[b]pyridine-3-carbo­nitrile and 2-meth­oxy-4-(thio­phen-2-yl)-5,6,7,8,9,10-hexa­hydrocyclo­octa[b]pyridine-3-carbo­nitrile

The title compounds, C(15)H(14)N(2)OS (1a), C(16)H(16)N(2)OS (1b), and C(17)H(18)N(2)OS (1c), form a homologous series in which the size of the saturated ring increases from six- to eight-membered (with four, five and six methyl­ene groups respectively). For 1b and 1c, the central (CH(2))( n ) moieties are all displaced to the same side of their ring, and the CH(2)—CH(2)—CH(2) angles are much wider than the standard sp (3) value; a database search indicates that these are general features of such ring systems. For 1a, the thio­phene ring lies with the sulfur atom on the opposite side of the C(thio­phene)—C(pyridine) bond to the cyano group, in contrast to 1b and 1c. For each compound, the packing may be described in terms of two ‘weak’ C—H⋯N hydrogen bonds, which link the mol­ecules to form one-dimensional (1a, 1c) or three-dimensional (1b) assemblies.