Correct option is D
Sigmatropic rearrangements are another class of concerted pericyclic reactions governed by orbital symmetry. This rearrangement involves a concerted reorganisation of electrons during which a group attached by a σ (sigma) bond migrates to the terminus of an adjacent π (pi) electron system. The reactions are called sigmatropic rearrangement because a σ (sigma) bond appears to move from one place to another during the reaction. There is a simultaneous shift of the π (pi) electrons. The number of the π (pi) and σ (sigma) bonds remain separately unchanged.
Sigmatropic rearrangements are classified by a double numbering system (i, j or m, n) that refers to the relative positions of the atom or group involved in the migration.
The above reaction is example of [1, 7] sigmatropic rearrangement.
E–Z configuration, or the E–Z convention, is the IUPAC preferred method of describing the absolute stereochemistry of double bonds in organic chemistry. It is an extension of cis–trans isomer notation (which only describes relative stereochemistry) that can be used to describe double bonds having two, three or four substituents. E and Z notation are only used when a compound doesn't have two identical substituents.
Following the Cahn–Ingold–Prelog priority rules (CIP rules), each substituent on a double bond is assigned a priority, then positions of the higher of the two substituents on each carbon are compared to each other. If the two groups of higher priority are on opposite sides of the double bond (trans to each other), the bond is assigned the configuration E. If the two groups of higher priority are on the same side of the double bond (cis to each other), the bond is assigned the configuration Z.
On C-3 and C-5 atoms, the higher priority groups are on the same side of the double bond. On C-7 atom, the higher priority groups are on the opposite side of each other.
