Unimolecular rectification based on voltage-controlled intramolecular stereochemical modification is suggested and computationally investigated. In sharp contrast to present molecular rectifiers, these conformational molecular rectifiers (CMRs) differ in principle from silicon structures, deriving their large, strongly temperature-dependent rectification from the differing current pathways in two dominant conformations, controlled by the interelectrode applied field. Two sorts of CMRs, one based on contact modulation the other on bridge modulation, are calculated: an ambient rectification ratio of 102 can be approached.