Answer:
Attached below diagram of the eight diastereomers
The Isomer that reacts so slowly is DIASTEREOMER 8
Step-by-step explanation:
The Isomer that reacts so slowly is DIASTEREOMER 8 in an E2 reaction and this is because no pair of chlorine and hydrogen atoms can assume the anti-periplanar orientation that is preferred in an E2 elimination
attached below is Diagram of the eight diastereomers ( screen shot from my drawing tool )