Question

If any two hydrogen of \(\mathrm{C}_{3} \mathrm{H}_{4}\) is replaced by phenyl substituent, then double bond equivalent of new compound obtained is (A) 8 (B) 6 (C) 10 (D) 9

Short answer

The new compound obtained after replacing two hydrogen atoms of C3H4 with phenyl substituents is C15H12. The double bond equivalent (DBE) of the new compound can be calculated using the formula: DBE = (C - H/2 + N/2 + 1). By plugging in the values, we get DBE = (15 - 12/2 + 0/2 + 1) = 10. So, the correct answer is (C) 10.

Step-by-step solution

Identify the Hydrocarbon Molecule and Phenyl Substituents

The given hydrocarbon molecule is C3H4, and we are to replace two of its hydrogens with phenyl substituents. A phenyl substituent is a benzene ring with one hydrogen removed, and has the formula C6H5.

Replace Two Hydrogens with Phenyl Substituents

Replacing two hydrogen atoms from C3H4 with phenyl substituents (C6H5) gives us the new compound: C3H4 + 2(C6H5) - 2 H --> C3H2(C6H5)2 or C15H12.

Calculate the Double Bond Equivalent (DBE) of the New Compound

Now, we can calculate the DBE of the new compound, C15H12, using the formula: DBE = (C - H/2 + N/2 + 1) DBE = (15 - 12/2 + 0/2 + 1) DBE = (15 - 6 + 0 + 1) DBE = 10

Choose the Correct Option

The double bond equivalent (DBE) of the new compound is 10. Therefore, the correct option is (C) 10.

Key concepts

Understanding Hydrocarbon Molecules

Hydrocarbon molecules form the basis of organic chemistry and are composed solely of carbon (C) and hydrogen (H) atoms. Understanding their structure is crucial, especially for students preparing for competitive exams like the JEE (Joint Entrance Examination) for engineering in India. The simplest hydrocarbons are alkanes, which have single bonds only. Moving further up, we encounter alkenes with carbon-carbon double bonds, and alkynes with carbon-carbon triple bonds.

For each additional double bond or ring in the structure, the molecule's double bond equivalent (DBE) increases. DBE is a crucial concept because it gives insight into the unsaturation within a molecule—the presence of double bonds, triple bonds, or rings. The formula to calculate DBE is given as: \[ DBE = C + 1 - \frac{H}{2} - \frac{X}{2} + \frac{N}{2} \]where C is the number of carbons, H is the number of hydrogens, X is the number of halogens, and N is the number of nitrogens. For organic chemistry students, grasping the importance of DBE is a step towards mastering molecular structure analysis and reactivity, pivotal for cracking exams like the JEE.

The Role of Phenyl Substituents in Organic Chemistry

In organic chemistry, a phenyl substituent (often represented as Ph) is a functional group derived from benzene, where one hydrogen atom is replaced by another chemical group. This group of atoms retains the aromatic characteristics of benzene, contributing significantly to the chemistry of the molecule it attaches to.

A phenyl substituent is not just an inert decoration; it can influence the molecule's physical properties and reactivity. Being a common substituent in organic molecules, phenyl groups can impact the polarity, solubility, and even the stability of various compounds. For JEE aspirants, understanding how substituents like the phenyl group behave in reactions is fundamental, as it forms part of the essential toolkit that can explain a wide range of organic chemistry phenomena. Knowing how to identify and count the number of phenyl substituents can also play a pivotal role in determining the compound's double bond equivalent, an essential step in structural determination problems.

Organic Chemistry for JEE Aspirants

Organic chemistry is a significant part of the JEE syllabus, challenging many students with its complexity. It involves the study of structure, properties, composition, reactions, and synthesis of organic compounds, predominately made from carbon atoms. JEE questions often test the student’s ability to understand and apply concepts such as double bond equivalents, functional groups, reaction mechanisms, and synthetic pathways.

One effective strategy to excel in organic chemistry is to methodically approach each problem. Start by identifying functional groups and the molecular framework. Then, use known mechanisms and concepts to unravel the reactions or properties in question. For instance, calculating the double bond equivalent (DBE) is a fundamental skill in identifying unsaturation in molecules—a task often presented in JEE. The DBE gives us a quick estimation of the number of π-bonds and rings in the compound, which is essential for understanding its reactivity and possible transformations. Diligent practice of these core concepts and problem-solving techniques is key to acing the organic chemistry section of the JEE.