LONE PAIRS IN CARBONYL-COMPOUNDS AND ETHERS

The effective locations of the lone pairs at the oxygens of formaldehyde, acetone, and diethyl ether were examined using several criteria: the minimum in the Laplacian of the charge density (rho), the minimum electrostatic potential, the position of hydrogen bonding to water and hydrogen fluoride, and the position of protonation. Whereas the charge density about a carbonyl or ether oxygen is essentially featureless, the Laplacian of rho and the electrostatic potential both show minima at locations that correspond to a common picture of the lone pairs. The interaction of a carbonyl oxygen with a lithium cation prefers a 180 degrees C-O-Li angle, whereas protonation prefers a 115 degrees C-O-H angle. Lewis acid bonding to formaldehyde prefers a C-O-M, angle of about 120 degrees. Hydrogen bonding leads to a very soft bending potential and C-O-H angles of about 120-130 degrees. This suggests that the geometries for hydrogen bonding found in X-ray crystallographic studies may in large measure be determined by crystal forces. The effect of substitution at the carbonyl group on the electrostatic potential also was studied.