It does not undergo the S_N1 reaction because of steric hindrance preventing it from being attacked by a nucleophile. It does not undergo the S_N2 reaction because the multi-ring structure prevents the sp² carbon in the carbocation formed from having a 120° bond angle making the carbocation unstable.

It does not undergo the S_N2 reaction because of steric hindrance preventing it from being attacked by a nucleophile. It does not undergo the S_N1 reaction because the multi-ring structure prevents the sp² carbon in the carbocation formed from having a 120° bond angle making the carbocation unstable.

It does not undergo the S_N1 reaction because of steric hindrance preventing it from being attacked by the leaving group. It does not undergo the S_N2 reaction because the multi-ring structure permits the sp² carbon in the carbocation formed having a 120° bond angle making the carbocation unstable.

It does not undergo the S_N2 reaction because of steric hindrance preventing it from being attacked by an electrophile. It does not undergo the S_N1 reaction because the multi-ring structure prevents the sp² carbon in the carbocation formed from having a 180° bond angle making the carbocation stable.