Question

Directions: Each question contains Statement-1 and Statement-2 and has the following choices (a), (b), (c) and (d), out of which ONLY ONE is correct. (a) Statement- 1 is True, Statement- 2 is True; Statement- 2 is a correct explanation for Statement-1 (b) Statement- 1 is True, Statement- 2 is True; Statement- 2 is NOT a correct explanation for Statement-1 (c) Statement-1 is True, Statement- 2 is False (d) Statement- 1 is False, Statement- 2 is True Statement 1 Erythro-2,3-dibromobutane on reaction with zinc and alcohol gives trans 2 -butene. and Statement 2 Elimination requires trans periplanar geometry.

Short answer

Question: Analyze the following two statements and determine the correct relationship between them: Statement 1: Erythro-2,3-dibromobutane on reaction with zinc and alcohol gives trans-2-butene. Statement 2: Elimination requires trans periplanar geometry. Answer: (a) Statement-1 is True, Statement-2 is True; Statement-2 is a correct explanation for Statement-1.

Step-by-step solution

Analyze Statement 1

First, we need to determine if erythro-2,3-dibromobutane reacts with zinc and alcohol to give trans-2-butene. It is essential to note that erythro-2,3-dibromobutane can undergo an anti-elimination reaction in the presence of zinc and alcohol. As a result, trans-2-butene will be formed. Hence, Statement 1 is true.

Analyze Statement 2

Now, we need to determine if the elimination requires a trans periplanar geometry. In general, elimination reactions follow an anti-periplanar geometry, meaning that the leaving groups or the hydrogen and halogen atoms are on opposite sides of the molecule. This alignment allows for the smooth flow of electrons during the elimination process. Thus, Statement 2 is also true.

Decide on the relationship between S1 and S2

Now that we know both statements are true, we need to decide whether S2 is a correct explanation for S1 or not. S1 represents the specific reaction of erythro-2,3-dibromobutane forming trans-2-butene, while S2 provides a general fact about elimination reactions requiring a trans periplanar orientation. Since anti-periplanar geometry is essential for the elimination mechanism happening in S1, we can say that S2 is a correct explanation for S1. Based on these steps, our answer is: (a) Statement-1 is True, Statement-2 is True; Statement-2 is a correct explanation for Statement-1.

Key concepts

Elimination Reaction

Elimination reactions are fundamental in organic chemistry, as they help remove atoms or groups from a molecule to form double or triple bonds. During such reactions, molecules undergo a transformation, where a nucleophile removes a leaving group.
Elimination can be classified as either E1 or E2 depending on the mechanism. E1 reactions occur in two steps, while E2 reactions happen in a single concerted step. In E2 reactions, the strong base and the molecule must align correctly for the reaction to proceed.
This alignment is due to the need for anti-periplanar geometry, which ensures the atoms being removed are on opposite sides of the molecule. Such configurations facilitate a more favorable reaction path by allowing the correct orbital overlap needed for the reaction.

Erythro-2,3-dibromobutane

Erythro-2,3-dibromobutane is a specific organic compound with two bromine atoms attached to the second and third carbon atoms in a butane chain. The term "erythro" indicates a specific stereochemistry where the substituents (in this case, the bromine atoms) are on the same side when looking at a Fischer projection.
This compound can serve as a starting material for various organic reactions. When erythro-2,3-dibromobutane reacts with zinc and alcohol, it undergoes an elimination reaction. The conditions provided by zinc and alcohol facilitate the removal of the bromine atoms and the formation of a double bond.

• This process results in the compound known as trans-2-butene.
• The orientation of the removed groups influences the type of isomer formed.

Trans-2-butene

Trans-2-butene is an alkene featuring a double bond between the second and third carbons in its carbon chain. The term "trans" denotes the spatial arrangement of the hydrogen atoms around the double bond.
In trans isomers, the hydrogen atoms are on opposite sides of the double bond. This configuration offers less steric strain compared to its cis counterpart, making the molecule generally more stable.
Organo-metallic reactions, such as the one using erythro-2,3-dibromobutane with zinc and alcohol, typically lead to the formation of trans-2-butene due to the anti-periplanar nature of the elimination reaction. This ensures efficient removal of atoms and formation of products.

Anti-periplanar Geometry

Anti-periplanar geometry is crucial in understanding elimination reactions, particularly E2 type reactions. This geometry dictates that the atoms or groups being removed must be positioned on opposite sides of the molecule.

• This alignment helps in achieving a lower energy transition state.
• It optimizes the overlap of p orbitals necessary for forming the double bond.

In the case of erythro-2,3-dibromobutane, the anti-periplanar requirement is fulfilled, allowing for smooth electron flow and facilitating the conversion to trans-2-butene.
The concept of anti-periplanar orientation emphasizes spatial arrangement, ensuring that the groups are suitably positioned to yield the intended alkenes, enhancing reaction predictability and control.