R. G. Azrak, E. Wilson
May 15, 1970
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Journal of Chemical Physics
Abstract
A proposed intramolecular hydrogen bond in the 2‐haloethanols has been investigated with analysis of the microwave spectra of 2‐chloroethanol and 2‐bromoethanol. For each moledule, only a form gauche about the CC bond has been observed. For the chloro compound nine isotopic species have been studied to yield the molecular coordinates of the chlorine, oxygen, hydroxyl hydrogen, and carbon atoms, and thus a molecular structure. For bromoethanol a molecular structure has been found based upon the coordinates of the bromine and hydroxyl hydrogen atoms. Principal structural conclusions are that, of the probable rotameric forms, the lowest energy form is the one allowing close approach of hydrogen and halogen—namely, the gauche–gauche for dihedral angles (CCX) (COH) close to 60°. The O–H bond length in chloroethanol is 1.008 A, about 5% longer than in ethanol. The H···X distance is ∼ 0.5 A less than the sum of the atom van der Waals radii for X = Cl, Br. The O···X distance is approximately equal to the sum of t...