Answer
IUPAC name and stereochemistry of Ocimene is
(3E)-3,7-Dimethylocta-1,3,6-triene
Work Step by Step
The compound has 8 carbon atoms in its longest chain and double bonds are present on the first, third and sixth positions respectively.
There are two methyl groups attached as substituents to the chain at position three and seven.
At $C_{3}$, $C_{4}$ double bond; we determine the priorities of the substituents attached on either side of the double bond.
On the left hand side of $C_{3}$ the whole carbon chain has a higher priority than the hydrogen attached to $C_{3}$ from the top.
On the right hand side of the $C_{4}$, the priority order is determined by comparing the atoms to which both the carbons are attached, since at $C_{4}$, both the substituents are carbon atoms. The one on the top is attached to another carbon atom while the $CH_{3}$ carbon is attached to H atoms. Thus the priority is given to the groups on opposite sides, giving the compound an E configuration.
