Which of the following give turbidity with Lucas reagent most readily.A) allyl alcoholB) dimethyl carbinolC) Diphenyl carbinolD) t-butyl carbinol(i thought ans is third as it is tertiary in structure but ans is third given) why?

To understand which compound gives the most turbidity with Lucas reagent, let's first clarify what Lucas reagent is and how it interacts with the different alcohols listed in your question. Lucas reagent is a solution of zinc chloride in hydrochloric acid, and it serves to differentiate between primary, secondary, and tertiary alcohols based on their reactivity.

Alcohol Reactivity and Lucas Reagent

When alcohols react with Lucas reagent, they undergo substitution to form alkyl chlorides. The rate at which this reaction occurs depends largely on the structure of the alcohol:

• Primary alcohols: React slowly, often requiring heat.
• Secondary alcohols: React moderately fast.
• Tertiary alcohols: React very quickly due to steric hindrance and the stability of the resulting carbocation.

Analyzing the Given Options

Now, let's take a closer look at each of the options you've provided:

• A) Allyl alcohol: This is a primary alcohol, which typically reacts slowly with Lucas reagent.
• B) Dimethyl carbinol: This is a secondary alcohol and will react faster than primary alcohols but not as quickly as tertiary alcohols.
• C) Diphenyl carbinol: This is a tertiary alcohol; however, it has bulky phenyl groups that can hinder the formation of the carbocation, leading to slower reactivity than expected.
• D) t-butyl carbinol: This is also a tertiary alcohol, and it reacts very rapidly with Lucas reagent because it forms a stable tertiary carbocation easily.

Why t-Butyl Carbinol is the Most Reactive

The key to understanding the reactivity lies in the stability of the carbocation formed during the reaction. Tertiary carbocations are more stable than secondary or primary ones due to hyperconjugation and inductive effects from surrounding alkyl groups. In the case of t-butyl carbinol, the positive charge on the carbon atom is stabilized by the three surrounding methyl groups, making it highly reactive with the Lucas reagent.

On the other hand, while diphenyl carbinol is tertiary, the presence of the bulky phenyl groups creates steric hindrance, which makes it less reactive than t-butyl carbinol. This is why, despite both being tertiary alcohols, t-butyl carbinol gives turbidity with Lucas reagent more readily than diphenyl carbinol.

Conclusion

In summary, the most rapid formation of turbidity with Lucas reagent is observed with t-butyl carbinol due to its ability to form a stable tertiary carbocation quickly. This reactivity pattern is a fundamental principle in organic chemistry that illustrates how structure influences chemical behavior. Understanding these concepts can greatly enhance your grasp of reaction mechanisms and the properties of organic compounds.