Question

Do double bonds really exist? Why

Answer 1

The double bond rule states that chemical elements with a principal quantum number greater than 2 for their valence electrons (period 3 elements and lower) should not form multiple bonds (e.g. double bonds and triple bonds) with themselves or with other elements.[1] The double bonds, when they exist, are often weak due to poor orbital overlap. Although such compounds are not intrinsically unstable, they instead tend to polymerize. This effect is manifested by the rapid polymerization that occurs upon condensation of disulfur, the heavy analogue of O2. This rule was challenged and ultimately disproven starting from 1981 with the isolation of crystalline samples of compounds with silicon–silicon and phosphorus–phosphorus double bonds. Double bonds that would ordinarily not form can often be stabilized with proper functional groups either electronically or sterically.