LONE PAIRS IN CARBONYL-COMPOUNDS AND ETHERS

The effective locations of the lone pairs at the oxygens of formaldehy de, acetone, and diethyl ether were examined using several criteria: t he minimum in the Laplacian of the charge density (rho), the minimum e lectrostatic 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. Th e 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 a bout 120 degrees. Hydrogen bonding leads to a very soft bending potent ial and C-O-H angles of about 120-130 degrees. This suggests that the geometries for hydrogen bonding found in X-ray crystallographic studie s may in large measure be determined by crystal forces. The effect of substitution at the carbonyl group on the electrostatic potential also was studied.