Question

Draw structures for each of the following: (a) m-Bromonitrobenzene (e) 2,4 -Dibromomesitylene (b) o-Ethyltoluene (f) Pheny 1 cyclohexane (c) \(p\) -Xylene (g) Biphenyl (d) 3-Nitrobenzene (h) Benzyl cyanide

Short answer

cid=9604) c) p-Xylene:  d) 3-Nitrobenzene:  e) 2,4-Dibromomesitylene:  f) Phenyl cyclohexane:  g) Biphenyl:  h) Benzyl cyanide: 

Step-by-step solution

a) m-Bromonitrobenzene

Draw the benzene ring and add a bromine (Br) and nitro (-NO2) substituent to the meta positions which means there is a carbon atom between the two substituents on the benzene ring. We will have the following structure: 

b) o-Ethyltoluene

Draw the benzene ring and add a methyl (CH3) substituent which is the structure of toluene. Then add an ethyl (C2H5) substituent at the ortho position, which means it is directly next to the methyl group. We will have the following structure: 

c) p-Xylene

Draw the benzene ring and add two methyl (CH3) substituents to the para positions which means there are two carbon atoms between the two substituents on the benzene ring. We will have the following structure: 

d) 3-Nitrobenzene

Draw the benzene ring and add a nitro (-NO2) substituent at the position 3 of the benzene ring. We will have the following structure: 

e) 2,4-Dibromomesitylene

Draw a benzene ring with three methyl (CH3) substituents at positions 2, 4, and 6. Then, add a bromine (Br) substituent at positions 2 and 4 of the methyl substituents. We will have the following structure: 

f) Phenyl cyclohexane

Draw a cyclohexane ring and add a phenyl (benzene ring) substituent to one carbon atom of the cyclohexane ring. We will have the following structure: 

g) Biphenyl

Draw two benzene rings connected to each other through a single carbon-carbon bond. We will have the following structure: 

h) Benzyl cyanide

Draw the benzene ring and add a benzyl group (single carbon atom connected to the benzene ring with an additional hydrogen atom: -CH2-) and then add a cyanide (-CN) group attached to the benzyl carbon. We will have the following structure: 

Key concepts

Aromatic Substitution

Aromatic substitution is a reaction where an atom, usually hydrogen, attached to an aromatic ring such as benzene, is replaced by another atom or group of atoms. This is a fundamental concept in organic chemistry, especially when discussing the derivatives of benzene. For instance, let's look at the formation of m-Bromonitrobenzene. Here, a hydrogen atom on the benzene ring is replaced by a bromine atom (Br), while another hydrogen atom is substituted by a nitro group (-NO₂). The 'm' indicates the substituents are in the meta position to each other, meaning they are separated by one carbon atom on the ring. Understanding the orientation and names of substituted benzene derivatives helps in predicting the physical and chemical properties of these compounds. Aromatic substitution reactions are often categorized as electrophilic aromatic substitution when an electrophile replaces the hydrogen atom.

Benzene Ring Derivatives

Benzene ring derivatives are compounds where the basic benzene ring has one or more substituents. These substituents can significantly alter the chemical behavior of the molecule. Derivatives like o-Ethyltoluene and p-Xylene have different substituents attached to the benzene ring at various positions. The 'o' (ortho) designation in o-Ethyltoluene means the methyl and ethyl groups are adjacent. In contrast, the 'p' (para) in p-Xylene means the methyl groups are opposite each other. These positional notations help in identifying the structure of benzene derivatives and are crucial in understanding their reactivity and potential applications. Derivatives of benzene rings form the backbone of many pharmaceuticals, dyes, and plastics, showcasing the practical importance of this area of study in organic chemistry.

Structural Isomers

Structural isomers are molecules that have the same molecular formula but differ in the way their atoms are connected. Considering 2,4-Dibromomesitylene, this compound is an isomer of other compounds with the same molecular formula but with bromine atoms in different positions or with different arrangements of the methyl groups. Isomers can have very different chemical and physical properties, which makes the study of isomerism essential for thoroughly understanding a chemical compound. Structural isomerism is contrasted with stereoisomerism, where isomers have the same bond structure but differ in the three-dimensional positioning of atoms. Isomers play a key role in organic synthesis and drug design, impacting the efficacy and safety of potential medications.

Functional Groups in Organic Chemistry

Functional groups are specific groups of atoms within molecules that have characteristic chemical behaviors no matter what they are attached to. The presence and type of functional groups help to classify organic compounds and predict their reactivity. In the exercise, Benzyl cyanide displays two functional groups: a benzyl group (-CH₂ attached to the benzene ring) and a cyanide group (-CN). Each group contributes distinct reactivity patterns, such as the benzyl group being prone to oxidation, while the cyanide group behaves as a nitrile, undergoing reactions such as hydrolysis. Learning about functional groups enables students to approach organic synthesis systematically, predict physical and chemical properties, and understand a compound's molecular behavior.