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

The absolute configuration of (+)-ethanol-1-<i>d</i> has been determined to be <i>R</i> 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 1<i>S</i>,4<i>R</i> in an X-ray anomalous dispersion study of the complex Cu<sub>2</sub>(camphanate)<sub>4</sub>(ethanol)<sub>2</sub>. These results provide unambiguous confirmation that the optical rotation of (<i>R</i>)-ethanol-1-<i>d</i> (positive) is opposite to that of its higher homologs, (<i>R</i>)-propanol-1-<i>d</i>, (<i>R</i>)-butanol-1-<i>d</i>, and (<i>R</i>)-neopentanol-1-<i>d</i> (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 (+)-(<i>R</i>)-ethyl-1-<i>d</i> (−)-(1<i>S</i>)-camphanate:  space group <i>P</i>2<sub>1</sub>2<sub>1</sub>2 (orthorhombic), <i>a</i> = 6.422(1) Å, <i>b</i> = 21.004(4) Å, <i>c</i> = 9.275(2) Å, <i>V</i> = 1251.1(7) Å<sup>3</sup>, <i>Z</i> = 4; <i>R</i>(<i>F</i><sup>2</sup>) = 0.083, and <i>wR</i>(<i>F</i><sup>2</sup>) = 0.075 for 1114 reflections. For the X-ray analysis of Cu<sub>2</sub>(camphanate)<sub>4</sub>(ethanol)<sub>2</sub>: space group <i>P</i>1 (triclinic), <i>a</i> = 11.086(3), <i>b</i> = 11.244(3), <i>c</i> = 13.293(4) Å, α = 111.59(2), β = 107.71(2), and γ = 105.56(3)°, <i>V</i> = 1397.6(7) Å<sup>3</sup>, <i>Z</i> = 1; <i>R</i>(<i>F</i>) = 0.054, <i>wR</i>(<i>F</i>) = 0.058 for 3672 reflections.