Free NEET Chemistry multiple-choice questions on Alkanes. Attempt each question and reveal the answer with a full explanation.
The most stable conformation of n -butane is: Anti-conformation Gauche conformation Partially eclipsed Fully eclipsed In the presence of light, the reaction of methane with an excess of chlorine yields which major product? CCl 4 CH 3Cl CH 2Cl 2 CHCl 3 Liquid hydrocarbons can be converted into a mixture of gaseous hydrocarbons by: Cracking Distillation under reduced pressure Oxidation Hydrolysis What is the correct order of reactivity of halogens towards the halogenation of alkanes? F 2 > Cl 2 > Br 2 > I 2 I 2 > Br 2 > Cl 2 > F 2 Cl 2 > F 2 > Br 2 > I 2 F 2 > Cl 2 > I 2 > Br 2 When methane is burnt in a limited supply of air or oxygen, it produces: Carbon black Carbon monoxide Carbon dioxide Methanol Which of the following alkanes has the highest boiling point? n -Pentane Isopentane Neopentane n -Butane Which of the following conformations of n -butane has the highest potential energy? Fully eclipsed Partially eclipsed Gauche Anti-staggered The correct order of boiling points for the following isomers of pentane is: n -pentane > isopentane > neopentane neopentane > isopentane > n -pentane isopentane > n -pentane > neopentane n -pentane > neopentane > isopentane The catalyst used in the manufacture of high-density polyethylene (HDPE) is: TiCl 4 + (C 2H 5) 3Al Pd/BaSO 4 V 2O 5 FeCl 3 According to the heat of combustion data, which of the following cycloalkanes is the most stable? Cyclohexane Cyclopentane Cyclobutane Cyclopropane The chlorination of methane is an example of: Free radical substitution Electrophilic substitution Nucleophilic substitution Electrophilic addition Pure methane can be prepared by: Soda lime decarboxylation of sodium acetate Wurtz reaction Reduction of methyl iodide with HI/P Kolbe's electrolysis Which of the following alkanes cannot be made in good yield by the Wurtz reaction? n-Heptane n-Butane n-Hexane 2,3-Dimethylbutane The number of hyperconjugative structures for the carbocation formed by the loss of Cl - from 2-chloropropane is: 6 3 9 0 Which of the following will have the lowest boiling point? Neopentane Isopentane n-Pentane n-Hexane In the Wurtz reaction, why is it necessary to use 'dry' ether as a solvent? To prevent the reaction of sodium with moisture, which would produce NaOH and H 2 To increase the solubility of the alkyl halide in the solvent To act as a catalyst for the formation of the carbocation To stabilize the alkane product through solvation What is the major product formed when aluminum carbide ( Al 4C 3 ) reacts with water? Methane Ethane Acetylene Ethylene Which of the following represents the correct order of C-C bond lengths? Ethane > Ethene > Ethyne Ethyne > Ethene > Ethane Ethane > Ethyne > Ethene Ethene > Ethane > Ethyne As branching increases in the isomers of an alkane, the boiling point generally decreases. This is because: The surface area decreases, leading to weaker Van der Waals forces The molecular mass decreases with branching The molecules become more polar with branching The intramolecular hydrogen bonding increases The dihedral angle in the most stable conformation of ethane is: 60 0 120 180 With respect to the conformers of ethane, which of the following statements is true? Bond angle remains same but bond length changes Bond angle changes but bond length remains same Both bond angle and bond length change Both bond angle and bond length remain same In the photochemical chlorination of methane, the step CH 3 + Cl 2 CH 3Cl + Cl is known as: Chain propagation step Chain initiation step Chain termination step Inhibition step Which of the following hydrocarbons is formed when sodium propionate is heated with soda lime? Ethane Methane Propane Butane Which of the following reagent sets is used for the Clemmensen reduction of a ketone to an alkane? Zn(Hg) / conc. HCl NH 2NH 2 / KOH / ethylene glycol LiAlH 4 / ether H 2 / Pd-C Alkanes can be prepared by the reaction of a Grignard reagent with: Water Dry ether Benzene Alkyl halide Which of the following radicals is most stable due to resonance? Allyl radical Vinyl radical Ethyl radical Methyl radical Which of the following will have the highest boiling point? n -Pentane Isopentane Neopentane n -Butane Which of the following alkanes cannot be prepared by the decarboxylation of a sodium salt of a carboxylic acid with soda lime? None of these Methane Ethane Propane The reaction of an alkyl halide with a finely divided metal like Ni or Pt in the presence of hydrogen gas to form an alkane is specifically known as: Sabatier-Senderens reaction Wurtz reaction Corey-House synthesis Kolbe's electrolytic method Which of the following represents the correct order of C-C bond length? Ethane > Ethene > Ethyne Ethyne > Ethene > Ethane Ethene > Ethane > Ethyne Ethane > Ethyne > Ethene Frankland's reaction is used to prepare higher alkanes from alkyl halides. The reagent used is: Zinc dust Sodium metal Magnesium ribbon Lithium metal The catalyst used in the hydrogenation of oils to fats is: Ni Fe Pt V2O5 Which of the following represents the correct order of the C-H bond length? C 2H 6 > C 2H 4 > C 2H 2 C 2H 2 > C 2H 4 > C 2H 6 C 2H 4 > C 2H 2 > C 2H 6 C 2H 6 > C 2H 2 > C 2H 4 The halogenation of alkanes in the presence of light follows which mechanism? Free radical substitution Electrophilic addition Nucleophilic substitution Electrophilic substitution A mixture of methane and steam when passed over nickel catalyst at 1273 K gives: CO + 3H 2 CO 2 + 2H 2 CH 3OH HCOOH The correct statement regarding the comparison of staggered and eclipsed conformation of ethane, is :- The staggered conformation of ethane is less stable than eclipsed conformation, because staggered conformation has torsional strain The eclipsed conformation of ethane is more stable than staggered conformation, because eclipsed conformation has no torsional strain The eclipsed conformation of ethane is more stable than staggered conformation even through the eclipsed conformation has torsional strain The staggered conformation of ethane is more stable than eclipsed conformation, because staggered conformation has no torsional strain. The correct statement regarding ethane conformation is : Rotation around carbon-carbon bond in ethane molecule is not possible, because ethane molecule contains both sigma(σ) bond and pi(π) bond between the carbon and carbon and ethane has very high boiling point. Rotation around carbon-carbon bond in ethane molecule is not possible, because ethane molecule contains a pi(π) bond between the carbon and carbon and ethane has very low melting point. Rotation around carbon-carbon bond in ethane molecule is not possible, because ethane molecule contains both sigma(σ) bond and pi(π) bond between the carbon and carbon. Rotation around carbon-carbon bond in ethane molecule is possible because of cylindrical symmetry of sigma(σ) bond between carbon-carbon atoms. Hydrocarbon (A) reacts with bromine by substitution to form an alkyl bromide which by Wurtz reaction is converted to gaseous hydrocarbon containing less than four carbon atoms. (A) is CH3-CH3 CH2=CH2 CH CH CH4 Weight (g) of two moles of the organic compound, which is obtained by heating sodium ethanoate with sodium hydroxide in presence of calcium oxide is : 16 32 30 18 Given below are two statements: Statement I : The boiling point of three isomeric pentanes follows the order n-pentane > isopentane > neopentane Statement II : When branching increases, the molecule attains a shape of sphere. This results in smaller surface area for contact, due to which the intermolecular forces between the spherical molecules are weak, thereby lowering the boiling point. In the light of the above statements, choose the most appropriate answer from the options given below: Both Statement I and Statement II are correct Both Statement I and Statement II are incorrect Statement I is correct but Statement II is incorrect Statement I is incorrect but Statement II is correct Methane reacts with steam at 1273 K in the presence of nickel catalyst to form : CO and H2 CO and H2O CO2 and H2 CO2 and H2O Which of the following alkanes cannot be prepared in good yield by the Wurtz reaction? n -Heptane Ethane Butane Hexane A mixture of ethyl iodide and methyl iodide is subjected to the Wurtz reaction. The product(s) formed is/are: Ethane, Propane, and Butane Propane only Ethane and Butane Butane only Which of the following methods is most suitable for the preparation of an unsymmetrical alkane like heptane from two different alkyl halides? Corey-House synthesis Wurtz reaction Frankland reaction Kolbe's electrolytic method The bond angle H-C-H in methane is: 109.5 107 120 180 The iodination of methane is carried out in the presence of oxidizing agents like HIO 3 or HNO 3 because: The reaction is reversible and HI needs to be removed I 2 is not reactive enough The reaction is highly exothermic To prevent the formation of multi-iodinated products Which of the following alkanes will give only one mono-chlorinated product upon photochemical chlorination? Neopentane n-Butane Isopentane 2,2,3,3-Tetramethylbutane The reaction of propene with Cl 2 at 500-600 C primarily gives: 3-Chloropropene 1,2-Dichloropropane 2-Chloropropene 1-Chloropropene Which of the following reactions can be used to prepare an alkane containing an odd number of carbon atoms from a single alkyl halide? None of these Wurtz reaction Kolbe's electrolysis Frankland reaction Sodium salt of which acid on heating with soda lime gives ethane? Propanoic acid Ethanoic acid Butanoic acid Methanoic acid In the presence of light, toluene reacts with chlorine to give: Benzyl chloride o-Chlorotoluene p-Chlorotoluene m-Chlorotoluene The Corey-House synthesis is specifically used to prepare which of the following types of alkanes more efficiently than the Wurtz reaction? Unsymmetrical alkanes Symmetrical alkanes Methane Cycloalkanes When n -butane is heated with anhydrous AlCl 3 and HCl gas at 300 K, the major product formed is: Isobutane 2-butene 1-butene Cyclobutane The general formula for the amount of oxygen required for the complete combustion of one mole of an alkane ( C nH 2n+2 ) is: (3n+1)/2 O 2 (n+1) O 2 n O 2 (3n+2)/2 O 2 Which free radical is the intermediate in the peroxide-initiated addition of HBr to propene? CH 3- C H-CH 2Br CH 3-CHBr- C H 2 C H 2-CH 2-CH 2Br C H 3 In the chain initiation step of chlorination of methane, the species formed is: Cl CH 3 Cl + Cl - Methane cannot be prepared by Kolbe's electrolytic method because: The methyl radicals combine to form ethane Methane is a gas Acetate ions do not discharge at the anode Methane is too reactive In the bromination of CH 3-CH 2-CH 3 at high temperature, the major product is 2-bromopropane. This is because: Secondary free radicals are more stable than primary free radicals Bromine is more reactive than chlorine Bromine is less selective than chlorine The C-H bond energy of a primary carbon is lower than that of a secondary carbon Heating n -hexane with AlCl 3 and HCl leads to the formation of: 2-Methylpentane and 3-methylpentane Benzene Cyclohexane Propane and butane The relative reactivity of 1 , 2 , and 3 hydrogen atoms towards chlorination at room temperature is in the ratio of: 1 : 3.8 : 5 1 : 82 : 1600 5 : 3.8 : 1 1 : 1 : 1 Which of the following reacts most rapidly with N -bromosuccinimide (NBS)? Cyclohexene Benzene n-Hexane Cyclohexane Which of the following compounds has the highest heat of combustion per methylene ( -CH 2- ) group? Cyclopropane Cyclobutane Cyclopentane Cyclohexane How many structural isomers are possible for the alkane C 6H 14 ? 5 4 6 7 Which of the following statements about the stability of conformations of n -butane is correct? Anti > Gauche > Partially Eclipsed > Fully Eclipsed Anti > Partially Eclipsed > Gauche > Fully Eclipsed Gauche > Anti > Partially Eclipsed > Fully Eclipsed Anti > Gauche > Fully Eclipsed > Partially Eclipsed In the reaction: CH 3CH 2Br + 2Na + BrCH 2CH 3 ether X + 2NaBr , the product X is formed by which mechanism? Free radical mechanism Nucleophilic substitution Electrophilic addition Carbene intermediate Which of the following orders is correct regarding the C-H bond energy? sp > sp 2 > sp 3 sp 3 > sp 2 > sp sp 2 > sp > sp 3 sp 3 > sp > sp 2 Which of the following has the highest boiling point? n-Pentane Isopentane Neopentane n-Butane Toluene reacts with excess chlorine in the presence of sunlight and heat to give: Benzotrichloride Benzyl chloride Benzal chloride o -chlorotoluene Which of the following free radicals is the most stable? (C 6H 5) 3C (CH 3) 3C CH 2=CH-CH 2 C 6H 5-CH 2 The pyrolysis (cracking) of propane at high temperatures typically yields a mixture of: Ethylene, Methane, Propene, and Hydrogen Only Ethane and Methane Only Propene and Hydrogen Carbon and Hydrogen only How many primary, secondary, and tertiary carbon atoms are present in 2,2,4-trimethylpentane respectively? 5, 1, 1 4, 2, 2 5, 2, 1 4, 1, 2 Methane reacts with steam at 1273 K in the presence of nickel catalyst to produce: A mixture of CO and H 2 (Synthesis gas) CO 2 and H 2O Methanol Ethane The Corey-House synthesis of alkanes involves the reaction between a lithium dialkylcuprate (Gilman reagent) and an alkyl halide. What is the general formula of the Gilman reagent? R 2CuLi RCuLi 2 R 3CuLi RMgX Photochemical monochlorination of isopentane (2-methylbutane) yields how many structural isomers? 4 3 2 5 The torsional angle in the 'skew' or 'gauche' conformation of ethane is: Any angle between 0 ∘ and 60 ∘ Exactly 60 ∘ Exactly 0 ∘ Exactly 120 ∘ What is the volume of oxygen required at STP for the complete combustion of 11.2 L of ethane ( C 2H 6 )? 39.2 L 22.4 L 11.2 L 44.8 L Which of the following alkanes has the lowest boiling point? 2,2-Dimethylpropane 2-Methylbutane n-Pentane n-Butane The catalyst used in the hydrogenation of ethene to ethane is: Raney Nickel Anhydrous AlCl 3 V 2O 5 FeCl 3 The Wurtz reaction of ethyl bromide and n -propyl bromide gives a mixture of alkanes. Which of the following is NOT a component of this mixture? n-Butane n-Pentane n-Hexane Isopentane The energy difference between the staggered and eclipsed conformations of ethane (torsional strain) is approximately: 12 kJ/mol 1 kJ/mol 45 kJ/mol 100 kJ/mol Reaction of propene with N-bromosuccinimide (NBS) in the presence of light yields: 3-Bromopropene 1-Bromopropene 2-Bromopropene 1,2-Dibromopropane Comparing n -hexane and 2,3-dimethylbutane, n -hexane has a higher boiling point because: It has a larger surface area for van der Waals forces It has a higher molecular weight It is more branched It has stronger hydrogen bonding The hydrolysis of beryllium carbide ( Be 2C ) produces which of the following hydrocarbons? Methane Ethane Acetylene Propine Which of the following is the most stable conformation of glycol ( HO-CH 2-CH 2-OH )? Gauche Anti Eclipsed Fully eclipsed In the presence of light, toluene reacts with Cl 2 to give benzyl chloride. If the reaction is continued with excess Cl 2 , the final product is: Benzotrichloride Benzal chloride p -chlorotoluene o -chlorotoluene The bromination of 2-methylpropane in the presence of light mainly yields: 2-bromo-2-methylpropane 1-bromo-2-methylpropane 2-bromobutane 1-bromobutane Complete combustion of a certain mass of an alkane gave 22 g of CO 2 and 10.8 g of H 2O . The alkane is: C 5H 12 C 3H 8 C 2H 6 C 4H 10 Which of the following alkane cannot be made in good yield by Wurtz reaction? 2,3-Dimethylbutane n-Heptane n-Butane n-Hexane Baeyer's Strain Theory is most applicable to: Cycloalkanes Alkanes Alkenes Aromatics Which isomer of C 6H 14 has only two types of non-equivalent hydrogen atoms? 2,3-Dimethylbutane n-Hexane 2-Methylpentane 3-Methylpentane Arrange the following in increasing order of stability of their most stable conformation: (i) Ethane, (ii) n-Butane, (iii) Cyclohexane. (ii) < (i) < (iii) (i) < (ii) < (iii) (iii) < (ii) < (i) (i) < (iii) < (ii) Reed's reaction is used to prepare which of the following compounds from alkanes? Alkyl sulfonyl chlorides Alkyl chlorides Nitroalkanes Alkanesulfonic acids Which of the following represents the correct order of the stability of cycloalkanes according to the Heat of Combustion per CH 2 group? Cyclohexane > Cyclopentane > Cyclobutane > Cyclopropane Cyclopropane > Cyclobutane > Cyclopentane > Cyclohexane Cyclohexane > Cyclopropane > Cyclobutane > Cyclopentane Cyclopentane > Cyclohexane > Cyclobutane > Cyclopropane Why is the bromination of alkanes much more selective than chlorination? The abstraction of a hydrogen atom by a bromine radical is endothermic and thus the transition state resembles the radical The abstraction of a hydrogen atom by a bromine radical is highly exothermic Bromine radicals are more reactive than chlorine radicals Chlorine is a larger atom and experiences steric hindrance The reactivity of halogens towards alkanes follows the order F 2 > Cl 2 > Br 2 > I 2 . Which step in the bromination of methane is endothermic? Abstraction of hydrogen from CH 4 by Br • Homolysis of Br 2 Reaction of CH 3 • with Br 2 Coupling of CH 3 • and Br • In the Corey-House synthesis, the reaction between R 2CuLi and R'X to form R-R' involves which type of mechanism? Nucleophilic substitution ( S N2 ) Electrophilic substitution Free radical substitution Electrophilic addition The reaction of n -butane with Cl 2 at 25 C in the presence of light gives a mixture of 1-chlorobutane and 2-chlorobutane. The percentage of 2-chlorobutane is approximately: 72% 28% 50% 99% How many products (including stereoisomers) are expected from monochlorination of the following compound? 6 2 3 5