Absolute Configuration of Chiral Ethanol-1-d:  Neutron Diffraction Analysis of the (−)-(1S)-Camphanate Ester of (+)-(R)-Ethanol-1-d

The absolute configuration of (+)-ethanol-1-d has been determined to be R by the single-crystal neutron diffraction analysis of its (−)-camphanate ester. The absolute configuration of the (−)-camphanate group, which served as the chiral reference for the neutron study, was in turn established to be 1S,4R in an X-ray anomalous dispersion study of the complex Cu2(camphanate)4(ethanol)2. These results provide unambiguous confirmation that the optical rotation of (R)-ethanol-1-d (positive) is opposite to that of its higher homologs, (R)-propanol-1-d, (R)-butanol-1-d, and (R)-neopentanol-1-d (all negative), and demonstrates the usefulness of neutron diffraction in determining the absolute configuration of molecules possessing chiral methylene groups (i.e., molecules of the type CHDRR‘). Crystallographic details:  for the neutron analysis of (+)-(R)-ethyl-1-d (−)-(1S)-camphanate:  space group P21212 (orthorhombic), a = 6.422(1) Å, b = 21.004(4) Å, c = 9.275(2) Å, V = 1251.1(7) Å3, Z = 4; R(F2) = 0.083, and wR(F2) = 0.075 for 1114 reflections. For the X-ray analysis of Cu2(camphanate)4(ethanol)2: space group P1 (triclinic), a = 11.086(3), b = 11.244(3), c = 13.293(4) Å, α = 111.59(2), β = 107.71(2), and γ = 105.56(3)°, V = 1397.6(7) Å3, Z = 1; R(F) = 0.054, wR(F) = 0.058 for 3672 reflections.