How many of the following specifically listed molecular structures will successfully exhibit Geometrical Isomerism? (i) 1,2-propadiene (ii) 2,3-pentadiene (iii) 2,3,4-hexatriene (iv) 1-Methylcyclohexy

Question

How many of the following specifically listed molecular structures will successfully exhibit Geometrical Isomerism? (i) 1,2-propadiene (ii) 2,3-pentadiene (iii) 2,3,4-hexatriene (iv) 1-Methylcyclohexylidene-4-acetic acid (v) Ortho-tetramethyl biphenyl.

Prashant Kotian · Accepted Answer

Correct answer: 1. (i) and (ii) are even cumulenes (perpendicular planes, no GI). (iii) is an odd cumulene with differing terminal groups ( and ), so it has co-planar ends and SHOWS GI. (iv) is an alkylidene cycloalkane with 1 ring + 1 pi bond = 2 stereogenic units (acts as even cumulene, perpendicular ends, no GI). (v) is heavily hindered biphenyl forced into perpendicular rings (no GI, shows optical activity). Only (iii) shows GI.

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