Question

Detection of unsaturation is carried by reaction with (A) \(\mathrm{Br}_{2} / \mathrm{CCl}_{4}\) (B) \(\mathrm{HBr}\) (C) \(\mathrm{Br}_{2} / \mathrm{H}_{2} \mathrm{O}\) (D) \(\operatorname{Both}(\mathrm{A})\) and \((\mathrm{C})\)

Short answer

The correct answer for detecting unsaturation is (D) Both (A) and (C), as both bromination reactions with Bromine in a non-polar solvent (\(Br_2/CCl_4\)) and Bromine in a polar solvent (\(Br_2/H_2O\)) are specific to the presence of double or triple bonds, causing visible color change.

Step-by-step solution

Understanding the given choices

First, let's understand each of the given reactions, their reactivity, and how they can relate to unsaturation detection. (A) \(Br_2 / CCl_4\): This is a bromination reaction where a molecule reacts with bromine in a non-polar solvent like carbon tetrachloride. (B) \(HBr\): This is a hydrobromination reaction where a molecule reacts with hydrogen bromide. (C) \(Br_2 / H_2O\): This is a bromination reaction where a molecule reacts with bromine in a polar solvent like water. (D) Both (A) and (C): Combination of choices A and C.

Analyzing reaction with Bromine in non-polar solvent \(Br_2/CCl_4\)

In the bromination reaction where a molecule reacts with bromine in a non-polar solvent like carbon tetrachloride, the reaction will only take place if there are double or triple bonds present in the molecule. The reaction will be as follows: \[ R_2C=CR_2 + Br_2 \rightarrow R_2CBr-CBrR_2 \] The presence of unsaturation will cause the reaction to take place, resulting in color change, which can then be observed visibly.

Analyzing reaction with Hydrogen Bromide (HBr)

In a hydrobromination reaction, a molecule reacts with hydrogen bromide to form a compound. This reaction will occur with both alkenes (double bonds) and alkynes (triple bonds) but will also occur with many other functional groups as well. Thus, this reaction will not be specific for detecting unsaturation.

Analyzing reaction with Bromine in polar solvent \(Br_2/ H_2O\)

In the bromination reaction where a molecule reacts with bromine in a polar solvent like water, the reaction will also take place only if there are double or triple bonds present in the molecule. The reaction will be as follows: \[ R_2C=CR_2 + Br_2 + H_2O \rightarrow R_2CBr-CBrR_2 + H_2O \] Similar to the reaction in a non-polar solvent, the presence of unsaturation will cause the reaction to take place and result in a color change, which can be observed visibly.

Concluding the best option for detecting unsaturation

Based on the analysis, it is clear that both the reaction with Bromine in a non-polar solvent (A: \(Br_2/CCl_4\)) and the reaction with Bromine in a polar solvent (C: \(Br_2/H_2O\)) are specific to detecting unsaturation due to their reactivity with the presence of double or triple bonds. Thus, the correct answer is (D) Both (A) and (C).

Key concepts

Bromination Reaction

A bromination reaction involves the addition of bromine (\(Br_2\)) to a molecule. This process typically targets unsaturated bonds, such as double or triple carbon-carbon bonds, within the molecule. - When bromine is added, it breaks these unsaturated bonds and forms new compounds known as vicinal dibromides.- The reaction's ability to transform unsaturated bonds into saturated vicinal dibromides makes it an excellent method to test for unsaturation.- An unsaturated compound will undergo a bromination reaction, which results in a visible change, often shown as a decolorization of the bromine's reddish-brown color. This reaction is valuable in organic chemistry to determine whether unsaturation (double or triple bonds) is present in a sample.

Non-Polar Solvent

A non-polar solvent, like carbon tetrachloride (\(CCl_4\)), does not have a significant charge separation across its molecules. These solvents are usually composed of molecules with similar electronegativities, resulting in an absence of significant dipoles. - In reactions like bromination, a non-polar environment supports the observation of unsaturation as bromination reactions occur clearly in such mediums because they do not interfere with the reaction mechanics.- Using a non-polar solvent provides a basis to visually detect the disappearance of the bromine color when it reacts with unsaturated compounds. This approach is widely used in laboratory settings to quickly identify the presence of unsaturation in an organic compound by observing the color change.

Polar Solvent

Polar solvents, on the other hand, have molecules with distinct positive and negative poles due to the difference in electronegativity between the bonded atoms. A common example is water (\(H_2O\)). - In bromination reactions, polar solvents can also act as the medium. They hold the capability to dissolve ionic and other polar compounds effectively.- When bromine dissolves in a polar solvent and interacts with unsaturated compounds, it facilitates the reaction by enhancing the interaction between bromine and the unsaturation sites, further leading to decolorization.- Polar solvents play a critical role in some reactions by offering a distinct pathway for the reaction to proceed. In bromination testing, they also allow the visible detection of unsaturation.