The physical properties of aldehydes and ketones are governed by the presence of the carbonyl group and its strong dipole moment. Due to differences in electronegativity, the carbon carries a strong partial positive charge, and the oxygen carries a strong partial negative charge. The dipole moments associated with the polar carbonyl groups of nearby molecules align, causing an elevation in boiling point of aldehydes and ketones relative to similar alkanes. However, aldehydes and ketones show lower boiling points than comparable alcohols because –OH groups can form hydrogen bonds, but carbonyls cannot.