Each Double-Bonded Carbon of an Alkene Has Three Sp2 Orbitals

4.3 structure of alkenes

Review of sublevels

-each double-bonded carbon of an alkene has three sp2 orbitals

-each of the sp2 orbitals overlaps an orbital of another atom to form a o bond-this bond contains two of the four electrons and is formed by a side-by-side overlap of singly occupied p orbitals of the two carbons

-the second carbon-carbon bond in the double bond is called the bond and is formed from side to side overlap of the remaining p orbitals of the sp2 carbons

-in order to achieve maximum orbital-orbital overlap, the two p orbitals must be parallel to each other so that all six atoms of the double bond system are in the same plane

-reminder that the bond represents the cloud of electrons that is above and below the plane defined by the two sp2 carbons and the four atoms bonded to them

4.3 cis-trans isomerism

?What would happen if there was rotation around the double bond?

-if there were rotation around the double bond than the two p orbitals would not overlap and the bond would break

-because rotation around a double bond is uncommon, an alkene such as 2-butene can exist in two forms

1.the hydrogens bonded to the sp2 carbons can be on the same side of the double bond or on the opposite sides of the double bond

?What is the name for nonidentical atoms with the same molecular formula?

isomers

cis-isomer-isomer with the hydrogens on the same side of the double bond

trans isomer-isomer with the hydrogens on different sides of the double bond

-cis and trans isomers are not possible for an alkene that has identical substituents attached to one of the double-bonded carbons

-cis and trans isomers can be interconverted only when the molecule absorbs sufficient heat or light energy to cause the bond to break

- bonds are weaker than o bonds