Structure and conformation of the N-β-propionic acids of cyclohexan[b]indole and cyclooctan[b]indole

The structures of cyclohexan[b]indole N-β-propionic acid (1) and cyclooctan[b]indole N-β-propionic acid (2) have been determined by X-ray methods. The conformational populations of their N-β-propionic chains have been determined in solution by 1H nmr analyses. Crystals of 1 are triclinic, space group [Formula: see text] with a = 12.3562(4), b = 11.0727(3), c = 10.2050(4) Å, α = 108.519(3), β = 83.941(3), γ = 104.826(3)°, and Z = 4. Crystals of 2 are monoclinic, space group P21/c, with a = 5.636(1), b = 18.937(3), c = 13.976(4) Å, β = 98.84(3)°, and Z = 4. In both structures, the molecules are linked forming dimers through centrosymmetric H bonds. In solution the trans conformation of the chain is the preferred one in both compounds and increases with dilution until a constant value is reached.