Aromatic compounds are organic compounds that are also referred to as “monocyclic and polycyclic aromatic hydrocarbons.” Benzene is the parent member. Heteroarenes are closely related because at least one carbon atom of the CH group is replaced by one of the heteroatoms oxygen, nitrogen, or sulphur. Furan, a heterocyclic compound with a five-membered ring containing a single oxygen atom, and pyridine, a heterocyclic compound with a six-membered ring containing one nitrogen atom, are two examples of non-benzene compounds with aromatic properties.
|Definition: Aromatic compounds are chemical compounds that consist of conjugated planar ring systems accompanied by delocalized pi-electron clouds in place of individual alternating double and single bonds.
They are also called aromatics or arenes. The best examples are toluene and benzene. Aromatics require satisfying Huckel’s rule. Plants and micro-organisms have an exclusive route to benzene-ring compounds. The great majority of aromatic compounds in nature, therefore, are produced by plants and micro-organisms, and animals are dependent upon plants for many aromatic compounds either directly or indirectly.
Aromatic Compounds Chemistry Questions with Solutions
Q1. Choose the correct statement related to aromatic hydrocarbon?
a.) It has only sigma bonds
b.) It has only pi bonds
c.) It has a sigma and two pi bonds
d.) It has a sigma and delocalized pi bond
Correct Answer– (d.) It has a sigma and delocalized pi bond
Q2. Aromatic compounds should have a π− electron cloud containing electrons. What cannot be the value of n?
Correct Answer– (c.) ½.
Explanation– Huckel’s rule states that only planar, fully conjugated monocyclic polyenes having 4n + 2 π electrons, where n is an integer, that is, n = 0, 1, 2, 3, 4, etc., should possess aromatic stability.
Q3. Out of the given options which one is aromatic?
a.) Cyclopentadienyl cation
d.) Cycloheptatrienyl cation
Correct Answer– (d.) Cycloheptatrienyl cation
Explanation– Since it has 6 electrons in its pi system, the cycloheptatrienyl (tropylium) cation is aromatic. It has a conjugated system, is planar, and is cyclic.
Q4. Out of the given options, which of the following is not aromatic?
b.) Cyclopentadienyl cation
c.) Cyclo-octatetraenyl dianion
d.) Tropyllium cation
Correct Answer– (b.) Cyclopentadienyl cation.
Explanation– Cyclopentadienyl cation does not follow Huckel’s Rule.
Q5. Aromatic hydrocarbons are–
c.) Both (a.) and (b.)
d.) None of the above
Correct Answer– (b.) unsaturated
Q6. State True or False.
Arenes are polar in nature.
Arenes are insoluble in water, which concludes that they are non-polar compounds.
Q7. Fill in the blank.
Aromatic hydrocarbon compounds containing benzene ring are known as ___.
Answer. Aromatic hydrocarbon compounds containing benzene ring are known as benzenoids.
Q8. What is aromatization? How will you convert n–hexane into benzene?
Answer. Aromatization is the process of converting alkanes with six or more carbon atoms into aromatic hydrocarbons that involves cyclization, isomerization, and dehydrogenation with the use of heat and a catalyst.
When n-hexane undergoes pyrolysis in presence of vanadium or chromium oxide as a catalyst and at high temperature and pressure forms benzene as a product.
Q9. Give some examples of aromatic compounds
Answer. Some examples of aromatic compounds are as follows-
Q10. Explain the Huckel’s Rule of Aromaticity.
Answer. Huckel’s rule states that only planar, fully conjugated monocyclic polyenes having 4n + 2 π electrons, where n is an integer, that is, n = 0, 1, 2, 3, 4, etc., should possess the aromatic stability. An aromatic compound must be planar and contain a cyclic cloud of π electrons below and above the plane of the molecule. It contains sp2 hybridized carbon atoms and must obey the Huckel rule.
According to this rule, the ring system must have (4n+2) π electrons, where n is any whole number (0, 1, 2, 3, etc). On this basis the ring systems which have 2(n=0), 6(n=1), 10(n=2), 14(n=3) etc pi electrons are aromatic. Typical examples of aromatic compounds are benzene, naphthalene, and anthracene.
Q11. What is the significance of aromatic hydrocarbons?
Answer. Aromatic hydrocarbons are commonly used as a non-polar solvent for other molecules. As a result, aromatic hydrocarbons can be used as additives in gasoline, paints, lacquers, and other products. Their low reactivity also helps them to be used as a solvent.
Q12. State the properties of Aromatic compounds.
Answer. The properties of Aromatic compounds are as follows-
- Arenes are mostly nonpolar and non-miscible in water.
- These compounds are usually unreactive and are used as solvents for various other nonpolar compounds.
- Their carbon to hydrogen ratio is high.
- They are characterized by sooty yellow flame.
Q13. What is the aromatic effect?
Answer. An aromatic ring current is a phenomenon seen in aromatic molecules like benzene and naphthalene. A ring current is induced in the aromatic ring’s delocalized electrons when a magnetic field is directed perpendicular to the plane of the aromatic system.
Q14. Give the difference between Aromatic and Aliphatic Compounds.
Answer. Following is the table explaining the difference between aromatic and aliphatic compounds:
|Parameter||Aromatic compounds||Aliphatic compounds|
|Structure||The linking of carbon compounds takes place in the ring structure with the help of conjugated pi electrons.||The linking of carbon compounds takes place in a straight line manner.|
|Flame test||A sooty flame is produced when burnt.||A sooty flame is not produced when burnt.|
|Odour||Pleasant odour.||Unpleasant odour.|
|Example||Benzene and naphthalene.||Butane and propane.|
Q15. Predict the major product for the following aromatic substitution reaction.
Answer. The major product for the substitution reaction is-
Practise Questions on Aromatic Compounds
Q1. Choose the incorrect statement–
a.) The aromatic hydrocarbon has a pleasant smell.
b.) Some of the aromatic compounds are ring-shaped.
c.) Aromatic hydrocarbon can be either mono or polycyclic.
d.) Benzene is the simplest hydrocarbon.
Q2. An aromatic compound must consist of-
a.) Cyclic molecule
b.) A planar structure
c.) A delocalized 𝜋 electron cloud
d.) All of the above
Q3. State True or False.
Benzene has a stronger Vander-Waal’s force than methybenzene.
Q4. How is the aromaticity of a compound judged?
Q5. Draw the following structures-
(D) 1,3,5-trimethyl benzene
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