Geometrical Isomerism

Geometrical isomerism is a type of stereoisomerism that arises due to the restricted rotation around a double bond or a ring. In geometrical isomerism, the arrangement of substituents around the double bond or ring differs, resulting in different spatial arrangements of the molecules.

Explanation of the options given

Let's analyze each option to determine which compound exhibits geometrical isomerism.

a) 1, 1-dichloro-1-pentene
In this compound, the double bond is between the first carbon and the second carbon. However, there are no substituents on either carbon atom, so there is no possibility of geometrical isomerism. Therefore, option A does not exhibit geometrical isomerism.

b) 1, 2-dichloro-1-pentene
In this compound, the double bond is between the first carbon and the second carbon, and there are two chlorine atoms attached to the second carbon. This arrangement allows for the possibility of geometrical isomerism. The two chlorine atoms can be either on the same side of the double bond (cis isomer) or on opposite sides (trans isomer). Hence, option B can exhibit geometrical isomerism.

c) 1, 3-dichloro-2-pentene
In this compound, the double bond is between the second carbon and the third carbon, and there are two chlorine atoms attached to the first carbon. This arrangement allows for the possibility of geometrical isomerism. The two chlorine atoms can be either on the same side of the double bond (cis isomer) or on opposite sides (trans isomer). Hence, option C can exhibit geometrical isomerism.

d) 1, 4-dichloro-2-pentene
In this compound, the double bond is between the second carbon and the third carbon, and there are two chlorine atoms attached to the fourth carbon. This arrangement allows for the possibility of geometrical isomerism. The two chlorine atoms can be either on the same side of the double bond (cis isomer) or on opposite sides (trans isomer). Hence, option D can exhibit geometrical isomerism.

Conclusion

From the analysis above, we can conclude that option A (1, 1-dichloro-1-pentene) does not exhibit geometrical isomerism, while options B, C, and D do exhibit geometrical isomerism. Therefore, the correct answer is option A.