Chemistry - STEREO ISOMERISM Question with Solution | TestHub

Ans. (C) S₄.

Sol. Spiro[4.4]nonane has its two identical rings locked perpendicular to each other (like the two ends of an allene, D₂d). A 90 deg rotation about the axis through the spiro carbon followed by reflection in the plane perpendicular to it maps the molecule onto itself, so it possesses an S₄ alternating axis.