Question

The incorrect statements regarding geometrical isomerism are: 
(A) Propene shows geometrical isomerism. 
(B) Trans isomer has identical atoms/groups on the opposite sides of the double bond. 
(C) Cis-but-2-ene has higher dipole moment than trans-but-2-ene. 
(D) 2-methylbut-2-ene shows two geometrical isomers. 
(E) Trans-isomer has lower melting point than cis isomer. 
 

• A. (A), (D) and (E) only
• B. (C), (D) and (E) only
• C. (B) and (C) only
• D. (A) and (E) only

Hint:

For geometrical isomerism to occur, different groups must be attached to the carbon atoms involved in the double bond.

Answer 1

The Correct Option is A

To determine the incorrect statements regarding geometrical isomerism, let's analyze each option:

1. Statement (A): Propene shows geometrical isomerism.
   Geometrical isomerism occurs in compounds with restricted rotation around a double bond and different groups attached to the carbons involved in the double bond. Propene has the structure CH₃-CH=CH₂, with one hydrogen and one methyl group on each of the double-bonded carbons. Since there are two identical hydrogen atoms on one of the double-bonded carbons, propene cannot show geometrical isomerism. Thus, statement (A) is incorrect.
2. Statement (B): Trans isomer has identical atoms/groups on the opposite sides of the double bond.
   This statement is correct. In trans isomers, identical groups are on opposite sides of the double bond, which differentiates them from cis isomers where identical groups are on the same side.
3. Statement (C): Cis-but-2-ene has higher dipole moment than trans-but-2-ene.
   Cis isomers generally have higher dipole moments compared to their trans counterparts due to the polarities of substituents on the same side of the double bond. Hence, statement (C) is correct for cis-but-2-ene and trans-but-2-ene.
4. Statement (D): 2-methylbut-2-ene shows two geometrical isomers.
   2-methylbut-2-ene has the structure (CH₃)₂C=CH-CH₃. As both substituents on one side of the double bond are identical (two methyl groups), there is no possibility of geometrical isomerism. Therefore, statement (D) is incorrect.
5. Statement (E): Trans-isomer has lower melting point than cis isomer.
   This statement is generally true for liquids, as trans isomers usually pack more tightly in a solid-state due to symmetry, resulting in higher melting points compared to cis isomers. However, the statement claims the opposite, so statement (E) is incorrect.

Thus, the incorrect statements are (A), (D), and (E). Therefore, the correct option is:

(A), (D) and (E) only