Chemistry - STEREO ISOMERISM Question with Solution | TestHub
For the conformation of lowest energy, estimate the atomic angles in the cation and the neutral molecule drawn below. Provide one number only for each question.
(a) C-O-C bond angle in the cation.
(b) C-O-C bond angle in the neutral molecule.
(c) C-O-C-C dihedral angle in the cation.
(d) C-O-C-C dihedral angle in the neutral molecule.
Options:
Answer:
Solution:
(a) 120° : in the cation the oxygen donates a lone pair into the empty p-orbital of C⁺, giving the C-O bond partial double-bond character; oxygen is effectively sp², so the C-O-C angle opens to about 120°.
(b) 108-110° : in the neutral ether oxygen is sp³ and the C-O-C angle is close to tetrahedral.
(c) 0° or 180° : maximum overlap between the oxygen lone pair and the empty p-orbital requires the C-O-C-C framework to be planar (syn or anti).
(d) 60° : in the neutral molecule the lowest energy conformation is gauche - the anomeric effect (n(O) σ*(C-O) overlap) prefers a dihedral of about 60°.
