During debromination of meso-dibromobutane, the major compound formed is (a) \(\mathrm{n}\) -butane (b) 1 -butane (c) cis-2-butene (d) trans-2-butene

Meso-dibromobutane is an organic molecule that has two bromine atoms added across opposite faces of a carbon-carbon bond in butane, specifically at the second and third carbon atoms. The prefix 'meso' indicates that the molecule has an internal plane of symmetry, meaning one half of the molecule is a mirror image of the other. This symmetry plays a crucial role in determining the properties of the compound, particularly in reaction outcomes. In debromination reactions, the two bromine atoms are removed, often with the aid of reagents like zinc in the presence of an acid or sodium iodide in acetone.

Understanding the structure of meso-dibromobutane is important for predicting the major product of debromination. Since it's a symmetrical molecule, we can anticipate that the product formed should also exhibit some level of symmetry, assuming no other rearrangements or side reactions occur.

Optical activity is a phenomenon observed in compounds that have the ability to rotate the plane of polarized light. This occurs due to the presence of chiral centers in the molecule, which are carbon atoms attached to four different groups. A compound is considered optically active if it can exist in two forms, known as enantiomers, that are non-superimposable mirror images of each other.

In the case of meso-dibromobutane, despite having stereocenters, it does not exhibit optical activity because the molecule has an internal plane of symmetry. This symmetry leads to the cancellation of the effects that individual chiral centers have on polarized light, rendering the molecule optically inactive. When undergoing reactions, the product formed from meso compounds typically retains the property of being optically inactive unless the symmetry of the molecule is disrupted.

Cis-2-butene is one of the two geometric isomers of 2-butene, where the two methyl (CH₃) groups are on the same side of the double bond. The term 'cis' signifies this arrangement. Geometric isomerism arises due to restricted rotation around double bonds, locking the substituents in a particular orientation. The presence of a cis configuration can impart different physical and chemical properties to the molecule compared to its 'trans' counterpart.

In the context of debromination of meso-dibromobutane, cis-2-butene is the major product because it retains the original plane of symmetry of the meso compound. It's noteworthy that unlike optical isomers, cis and trans isomers may or may not have optical activity. Cis-2-butene, being symmetrical and lacking chiral centers, is optically inactive. This characteristic is aligned with keeping the symmetry and optical inactivity originally present in meso-dibromobutane.