Comparison crystal structure conformations of two structurally related biphenyl analogues: 4,4′-bis­[3-(pyrrolidin-1-yl)prop-1-yn-1-yl]-1,1′-biphenyl and 4,4′-bis­{3-[(S)-2-methyl­pyrrolidin-1-yl]prop-1-yn-1-yl}-1,1′-biphen­yl

The title compounds, C(26)H(28)N(2), (I), and C(28)H(32)N(2), (II), were designed based on the structure of the potent α9α10 nicotinic acetyl­choline receptor antagonist ZZ161C {1,1′-[[1,1′-biphen­yl]-4,4′-diylbis(prop-2-yne-3,1-di­yl)]bis­(3,4-di­methyl­pyridin-1-ium) bromide}. In order to improve the druglikeness properties of ZZ161C for potential oral administration, the title compounds (I) and (II) were prepared by coupling 4,4′-bis­(3-bromo­prop-1-yn-1-yl)-1,1′-biphenyl with pyrrol­idine, (I), and (S)-2-methyl­pyrrolidine, (II), respectively, in aceto­nitrile at room temperature. The asymmetric unit of (I) contains two half mol­ecules that each sit on sites of crystallographic inversion. As a result, the biphenyl ring systems in compound (I) are coplanar. The biphenyl ring system in compound (II), however, has a dihedral angle of 28.76 (11)°. In (I), the two independent mol­ecules differ in the orientation of the pyrrolidine ring (the nitro­gen lone pair points towards the biphenyl rings in one mol­ecule, but away from the rings in the other). The torsion angles about the ethynyl groups between the planes of the phenyl rings and the pyrrolidine ring N atoms are 84.15 (10) and −152.89 (10)°. In compound (II), the corresponding torsion angles are 122.0 (3) and 167.0 (3)°, with the nitro­gen lone pairs at both ends of the mol­ecule directed away from the central biphenyl rings.