The structure and conformation of 1-phenyl-2-methylcyclopropene-3-carboxylic acid and cis­2-(m-nitrophenyl)cyclopropanecarboxylic acid

The structures of cis-2-(m-nitrophenyl)cyclopropanecarboxylic acid (1) and 1-phenyl-2-methylcyclopropene-3-carboxylic acid (2) have been determined by X-ray methods. Crystals of 1 are triclinic, space group [Formula: see text], with a = 7.422, b = 8.615, c = 9.499 Å, α = 60.24, β = 63.76, γ = 71.36°, and two molecules in the unit cell. Crystals of 2 are monoclinic, space group P21/c, with four molecules in a unit cell of dimensions a = 9.345, b = 13.286, c = 8.187 Å, and β = 98.22°. The carboxyl group of 1 approaches the bisecting conformation. The phenyl group is 37° from this conformation, by contrast with the unhindered compound 2-(p-nitrophenyl) cyclopropyl methyl ketone. In 2 the carboxyl group bisects the three-membered ring, indicating that carbonyl-cyclopropene π interactions can occur if sterically allowed. The two rings are essentially coplanar, permitting maximum interaction of the phenyl group and the double bond. In both compounds, the carbonyl oxygen of the carboxyl is the nearer oxygen to the three-membered ring.