This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Functional Chemistry of Graphene”.
1. What kind of cycloaddition functionalization of graphene results in six-membered ring?
a) Huisgen cycloaddition
b) Diels-Alder cycloaddition
c) Nitrone-olefin cycloaddition
d) Iron-catalysed olefin cycloaddition
View Answer
Explanation: There are several types of cycloaddition reactions. Cycloaddition functionalization of graphene involving formation of six membered ring [4+2] can be obtained through the Diel-Alder cycloaddition. It is a famous pericyclic reaction involving a conjugated diene and a dienophile.
2. Which is the most stable isomeric configuration in graphene?
a) Washboard
b) Chair
c) Twist-boat
d) Tricycle
View Answer
Explanation: Graphene exhibits a number of stable isomers with chair, stirrup and boat configurations. However, studies have revealed that chair configuration is the most stable out of all other configurations. Here, the hydrogen atoms are alternately absorbed above and below the graphene sheet.
3. Which of the following method is not applied for oxidation of graphene?
a) Hummer’s method followed by exfoliation
b) Treatment of graphene with DMF
c) Treatment of graphene with concentrated nitric acid
d) Cutting and unraveling of carbon nanotubes, lengthwise
View Answer
Explanation: There are various methods of oxidation of graphene. First, treating graphene directly with strong oxidants such as nitric acid (HNO3), sulphuric acid (H2SO4) etc. Second, graphite oxidation via Hummer’s method followed by exfoliation. Third, oxidation of graphene by lengthwise cutting and untangling of the carbon nanotubes (CNTs).
4. What causes the flattening of TMPyP molecules?
a) Spring forces
b) Poor π-π stacking
c) Electrostatic forces
d) Hydrophilic interactions
View Answer
Explanation: 5, 10, 15, 20-tetrakis (1-methyl-4-pyridino) porphyrin (TMPyP) molecules can be placed onto the reduced graphene oxide (rGO) sheets in a monolayer by electrostatic interactions and π-π stacking. These strong non-covalent interactions between the two components result in the molecular flattening of TMPyP molecules. rGO sheets that are functionalized with TMPyP can be utilized to detect Cd2+ ions rapidly and selectively.
5. What is a fully hydrogenated graphene called?
a) Pristine graphene
b) Graphite
c) Hydrogenated graphene
d) Graphane
View Answer
Explanation: Fully hydrogenated graphene is referred to as Graphane. Ideally, every carbon atom of the graphene layer is covalently bonded to hydrogen atom. This leads to the change in the hybridization of carbon atoms in graphene from sp2 to sp3. Consequently, the graphene layer gets buckled.
6. Choose the incorrect option with respect to the types of cycloaddition functionalization of graphene.
a) Cycloaddition forming four-membered ring
b) Cycloaddition forming six-membered ring
c) Cycloaddition forming seven-membered ring
d) Cycloaddition forming five-membered ring
View Answer
Explanation: Cycloaddition functionalization of graphene includes four types in accordance with the atom number of the addition ring. These types involves: [2+1] cycloaddition forming a three-membered ring, [2+2] cycloaddition forming a four-membered ring, [3+2] cycloaddition forming a five-membered ring, [4+2] cycloaddition forming a six-membered ring.
7. Choose the correct option from the following statements.
a) Hydrogenated graphene has optical properties extremely similar to pristine graphene
b) Partially hydrogenated graphene does not show any magnetic properties
c) Lowering the degree of hydrogenation of graphene widens the bandgap
d) Hydrogenation enhances the elasticity of graphene sheets
View Answer
Explanation: Hydrogenation of graphene leads to several changes in its properties and electronic structure. Increasing the degree of hydrogenation of graphene widens the bandgap. It further enhances the elasticity of graphene sheets. Hydrogenated graphene shows optical properties that are way different from pristine graphene. Also, partially hydrogenated graphene has magnetic properties.
8. Why is cycloaddition reaction different from most typical organic reactions?
a) Participation of only cations in reaction as intermediates
b) Participation of only anions in reaction as intermediates
c) Participation of neither anions nor cations in reaction as intermediates
d) Participation of both anions and cations in reaction as intermediates
View Answer
Explanation: Cycloaddition reaction is a chemical reaction involving the combination of two or more unsaturated molecules resulting in the formation of a cyclic adduct. These reactions are quite different from most typical organic reaction since these reactions do not produce cations or anions as intermediates. They instead involve the circular movement of electrons with simultaneous bond cleavage and bond formation.
9. Which of the following is not included in the non-covalent functionalization of graphene?
a) π-π stacking
b) Electrostatic interactions
c) Hydrogen bonding
d) Free radical addition
View Answer
Explanation: The non-covalent functionalization of graphene includes placement of functional species onto the graphene sheets via electrostatic forces, π-π stacking, hydrophobic interactions and hydrogen bonding. Free radical addition, on the other hand, falls under the category of covalent functionalization of graphene basal plane. The non-covalent functionalization of graphene can be achieved by polymer wrapping, adsorption of surfactants etc.
10. Choose the correct decreasing order for the stability of the isomeric configurations of graphane.
a) Boat > Stirrup > Chair
b) Zig-Zag > Boat > Chair
c) Chair > Washboard > Boat
d) Chair > Boat > Zig-Zag
View Answer
Explanation: Fully hydrogenated graphene called graphane exhibits several isomers including chair, stirrup, twist-boat, tricycle, armchair configurations. There are many more structures. However, chair, stirrup and boat are among the most stable configurations. Out of these chair is the most stable followed by stirrup and boat. Stirrup is also known as zig-zag or washboard configuration.
11. The bandgap of graphene remains unaltered with functionalization of its edges.
a) True
b) False
View Answer
Explanation: The edge carbon atoms of graphene are more reactive than those of the basal plane. Their functionalization can improve both the solubility and assembly behavior of graphene. In contrast to graphene basal plane, functionalization of edge carbon atoms do not lead to any changes in bandgap, since the sp2 network remains undisturbed.
Sanfoundry Global Education & Learning Series – Nanotechnology.
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