On heating, the compound $\mathrm{Z}$ undergoes a series of 1,5-H/D shifts to give a mixture of its isomers.

The total number of isomers present in the mixture (including $\mathrm{Z}$) is (in integer).

Question

Reaction that yields P as the major product is

Answer 1

This question is about the classic degenerate rearrangement of cyclopentadiene, where the single $\mathrm{sp^3}$ carbon of the ring walks all the way around through a chain of thermal $[1,5]$-sigmatropic H (or D) shifts.

Starting point: $\mathrm{Z}$ has an $\mathrm{sp^3}$ ring carbon carrying one H and one D on two distinct faces (shown by the wedge and dash bonds), plus a second, separate D sitting on one of the four vinylic ring carbons.
Mechanism: In a $[1,5]$-shift, the migrating atom on the $\mathrm{sp^3}$ carbon moves suprafacially across the adjacent conjugated diene to the far ring carbon, which becomes the new $\mathrm{sp^3}$ centre; the carbon that is left behind becomes part of the new diene, keeping whichever of H or D did not migrate.
Effect of the ring closure: because the $\mathrm{sp^3}$ carbon is bonded to both ends of the diene system, the walk can proceed toward either ring neighbour, with the suprafacial requirement locking a specific face (and hence a specific isotope) to each direction of travel.
Repeating the walk: sending the $\mathrm{sp^3}$ position all the way around the five ring carbons, and tracking whenever it meets and interacts with the second, originally fixed ring D, generates a set of distinct isotopically labelled cyclopentadienes.

Collecting every position/label combination this walk reaches, and merging any pair of structures that are secretly identical by the unlabelled ring's own symmetry, leaves 9 distinguishable isotopomers in the final mixture, with $\mathrm{Z}$ counted as one of them.

Let's summarize:

Thermal $[1,5]$-H/D shifts move the $\mathrm{sp^3}$ carbon of a cyclopentadiene around the ring one position at a time.
With two isotopic labels present (the H/D pair on the mobile carbon and the fixed ring D), the walk generates several distinguishable structures rather than just one.
The full accessible set, including the starting compound $\mathrm{Z}$, has 9 members.

The total number of isomers present in the mixture, including $\mathrm{Z}$, is 9.

Answer 2

This question is about the classic degenerate rearrangement of cyclopentadiene, where the single $\mathrm{sp^3}$ carbon of the ring walks all the way around through a chain of thermal $[1,5]$-sigmatropic H (or D) shifts.

Starting point: $\mathrm{Z}$ has an $\mathrm{sp^3}$ ring carbon carrying one H and one D on two distinct faces (shown by the wedge and dash bonds), plus a second, separate D sitting on one of the four vinylic ring carbons.
Mechanism: In a $[1,5]$-shift, the migrating atom on the $\mathrm{sp^3}$ carbon moves suprafacially across the adjacent conjugated diene to the far ring carbon, which becomes the new $\mathrm{sp^3}$ centre; the carbon that is left behind becomes part of the new diene, keeping whichever of H or D did not migrate.
Effect of the ring closure: because the $\mathrm{sp^3}$ carbon is bonded to both ends of the diene system, the walk can proceed toward either ring neighbour, with the suprafacial requirement locking a specific face (and hence a specific isotope) to each direction of travel.
Repeating the walk: sending the $\mathrm{sp^3}$ position all the way around the five ring carbons, and tracking whenever it meets and interacts with the second, originally fixed ring D, generates a set of distinct isotopically labelled cyclopentadienes.

Collecting every position/label combination this walk reaches, and merging any pair of structures that are secretly identical by the unlabelled ring's own symmetry, leaves 9 distinguishable isotopomers in the final mixture, with $\mathrm{Z}$ counted as one of them.

Let's summarize:

Thermal $[1,5]$-H/D shifts move the $\mathrm{sp^3}$ carbon of a cyclopentadiene around the ring one position at a time.
With two isotopic labels present (the H/D pair on the mobile carbon and the fixed ring D), the walk generates several distinguishable structures rather than just one.
The full accessible set, including the starting compound $\mathrm{Z}$, has 9 members.

The total number of isomers present in the mixture, including $\mathrm{Z}$, is 9.

On heating, the compound \(\mathrm{Z}\) undergoes a series of 1,5-H/D shifts to give a mixture of its isomers.

The total number of isomers present in the mixture (including \(\mathrm{Z}\)) is (in integer).

Show Hint

Correct Answer: 9

Solution and Explanation

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On heating, the compound \(\mathrm{Z}\) undergoes a series of 1,5-H/D shifts to give a mixture of its isomers. The total number of isomers present in the mixture (including \(\mathrm{Z}\)) is (in integer).