This set of Organic Chemistry Question Paper focuses on “Displacement Substitution Reaction & Electron Movement”.
1. Which of the following statement is false for substitution reaction?
a) One functional group in a compound replaces another functional group
b) We can classify substitution reaction by nucleophile and electrophile
c) We can classify substitution reaction only by nucleophile and electrophile
d) Substitution reactions are divided into three general classes, depending on the type of atom or group that acts as the substituent
Explanation: The substitution reaction can be classified by an electrophile or a nucleophile, whether a reactive intermediate involved in the reaction is a carbocation, a carbanion or a free radical.
2. Why the chloroform layer becomes purple, when a colourless solution of potassium iodide is passed through a colourless solution of chloroform?
c) Potassium chloride
d) Potassium iodide
Explanation: The iodine so liberated, dissolves in the chloroform, giving it a purple colour.
2KI + Cl2 –> 2KCl + I2
3. A layer of reddish brown precipitate which is formed on the iron knife, when an iron knife is dipped in an aqueous solution of copper sulphate is of which compound or element?
a) Iron sulphate
d) Copper sulphate
Explanation: copper produced in the below reaction will be deposited on iron knife gives reddish brown colour.
Fe + CuSO4 –> FeSO4 + Cu
4. What is the correct order of reactivity series of the halogen?
a) F > Cl > Br > I
b) I > Cl > Br > F
c) F > Br > Cl > I
d) I > Br > Cl > F
Explanation: As we know size of F < Cl < Br < I increases down the group in periodic table. Due to the increase in the radius and the extra shielding in the atom, which means that an electron is more easily attracted into the outer shell of a larger atom leads to than the smaller atom. So, reactivity is more of smaller size atoms.
5. Which of the following is a not method of electron movement?
a) Bond breaking
b) Bond making
c) Bond movement
d) Revolution of bond
Explanation: In bond breaking, bond making and bond movement, the electrons are moved between atoms or compounds. This is because all of them have the property of electron transfer or we can say the movement of a pair of electrons from an electron rich site (a lone pair of electrons or a bond) to an electron poor site. But revolution of bond will not lead to movement of electron between compounds.
6. Which of the following statement is false for electron movement?
a) The formal charge becomes one unit more positive at the starting atom and one unit more negative at the terminal atom
b) The last arrow in a chain must be either a bond making arrow terminating at a sextet atom, or a bond breaking arrow.
c) When a bond is broken, this is represented by a curved arrow pointing towards from the bond from which electron will be transfered and ending the arrow pointing away towards the next unoccupied molecular orbital
d) Curly arrows are superimposed over the structural formulae of reactants in a chemical equation to show the reaction mechanism
Explanation: Due to accepting an electron, the species shows negative charge and the donating will experience positive charge. The last arrow pushing will show which atom will have what character, so it should be either breaking or making arrows. If the sigma bond is breakable, donation of electrons become easy.
7. Who proposed arrow pushing method of showing progression of electons?
a) Sir Robert Robinson
b) Robert Burns Woodward
c) Adolf Von Baeyer
d) Victor Grignard
Explanation: arrow pushing was proposed by Sir Robert Robinson to show movement of electron within a molecule or between two different species. Curved arrow or curly arrow is used to represent the transfer of electrons.
8. Electrons movement take place from __________
a) positively to negatively components
b) negatively to positively charged components
c) neutral to charged species
d) charged species to neutral
Explanation: Electrons are negatively charged means electron rich spices, and so are attracted to the positive side and repelled by the negative side. So when the transfer takes place the electrons flow through it, they flow from negative to positive species.
9. Which species are formed due to Homolytic bond breakage?
c) Free radical
Explanation: In homolytic cleavage sharing of unpaired electrons on each of the atoms that were formerly joined by a bond, takes place. This leads to the formation of free radicals.
10. Which of the following type of reaction shows heterolytic bond cleavage?
a) SN1 reaction
b) Addition reaction
c) Elimination reaction
d) Free radical halogenation
Explanation: In SN1, Addition and Elimination reaction, distribution of electrons after bond cleavage is different. The electrons are transferred to more electronegative atoms. But Splitting or homolysis of a chlorine molecule, to form two chlorine atoms, initiated by ultraviolet radiation or sunlight. A chlorine atom has an unpaired electron and acts as a free radical.
Sanfoundry Global Education & Learning Series – Organic Chemistry.
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