A covalent bond in which two electron pairs (instead of the usual one) are shared between two atoms; most common between carbon atoms and carbon, oxygen or nitrogen atoms, but several other forms are known
Two atoms sharing electrons as in a °single bond (that is, a °sigma bond) may also share electrons in an orbital with a node passing through the two atoms This adds a second, weaker bonding interaction (a °pi bond); the combination is termed a double bond A twisting motion that forces the nodal plane at one atom to become perpendicular to the nodal plane on the other atom eliminates the (signed) °overlap between the atomic orbitals, destroying the pi bond The energy required to do this creates a large barrier to rotation about the bond (see °triple bond)
A structure formed when adjoining carbon atoms in the carbon chain of a saturated fatty lose two hydrogen atoms Double bonds may be either in the cis or trans orientation