Alkanes: preparation (Wurtz, Kolbe, decarboxylation) and reactions

37 questions on Alkanes: preparation (Wurtz, Kolbe, decarboxylation) and reactions from the Hydrocarbons chapter: 8 NEET level, 14 JEE Main, 15 JEE Advanced. Each one opens with its answer and solution.

• Sodium metal in dry ether is heated with an equimolar mixture of CH3Br and CH3CH2Br (Wurtz reaction). How many different alkanes are formed? NEET level
• Heating sodium propanoate, CH3CH2COONa, with soda lime (NaOH + CaO) gives mainly NEET level
• In the Kolbe electrolysis of concentrated aqueous sodium acetate, the hydrocarbon product is formed at the NEET level
• The first (chain initiation) step in the photochemical chlorination of methane is NEET level
• 2-Bromopropane is treated with sodium metal in dry ether. The main organic product is JEE Main level
• Kolbe electrolysis of aqueous potassium succinate, KOOC-CH2-CH2-COOK, gives at the anode JEE Main level
• Rotation about the C2-C3 bond of n-butane produces several conformations. The conformation of highest energy is the one in which JEE Main level
• 3-Methylpentane, CH3CH2CH(CH3)CH2CH3, undergoes free radical monochlorination. Counting every stereoisomer (each enantiomer and each diastereomer) as a separate... JEE Main level
• Propane, CH3CH2CH3, is monochlorinated by free radicals at 25 degC. Take the relative rates of abstraction per hydrogen as primary : secondary =1:3.8. The perce... JEE Main level
• Bromination of 2-methylpropane gives almost exclusively 2-bromo-2-methylpropane, whereas chlorination gives a mixture. The best explanation is that JEE Main level
• Which of the following would give a single pure alkane (apart from inorganic by-products) as the only hydrocarbon product? JEE Main level
• An alkane-forming intramolecular Wurtz cyclisation of a dibromoalkane (sodium, dry ether) gives a cycloalkane which on free radical monochlorination gives only ... JEE Advanced level
• A charge of 0.4 F is passed through concentrated aqueous sodium acetate between inert electrodes. Assume that only acetate is oxidised at the anode (Kolbe react... JEE Advanced level
• 2-Methylbutane is monochlorinated by free radicals using relative rates per hydrogen of primary : secondary : tertiary =1:3.8:5. Ignoring stereoisomers (each co... JEE Advanced level
• The dihedral angle between the two methyl groups of n-butane (about C2-C3) is changed from 180 deg to 0 deg in steps, passing through 120 deg and 60 deg. The co... JEE Advanced level
• An alkyl bromide A (C4H9Br) is treated with sodium in dry ether to give an alkane B. Free radical monochlorination of B gives exactly three constitutional isome... JEE Advanced level
• Which of the following statements about free radical halogenation of alkanes are correct? JEE Advanced level
• An equimolar mixture of sodium propanoate and sodium 2-methylpropanoate is electrolysed in concentrated aqueous solution (Kolbe conditions). Consider only radic... JEE Advanced level
• A mixture of CH3Br and C2H5Br is treated with sodium metal in dry ether (Wurtz reaction). How many different alkanes are formed? NEET level
• Heating sodium butanoate, CH3CH2CH2COONa, with soda lime gives mainly: NEET level
• On electrolysis of a concentrated aqueous solution of sodium acetate, the gaseous products at the anode are: NEET level
• In the free radical chlorination of methane, which of the following is a chain propagation step? NEET level
• Wurtz reaction of 2-bromopropane alone (sodium, dry ether) gives: JEE Main level
• Use the relative rates of hydrogen abstraction by chlorine radical, primary : secondary : tertiary = 1 : 3.8 : 5. The percentage of 2-chloropropane in the monoc... JEE Main level
• How many monochlorination products (constitutional isomers only; stereoisomers are not counted separately) can be formed from 2-methylbutane, (CH3)2CH-CH2-CH3, ... JEE Main level
• Rotation about the C2-C3 bond of butane gives anti (A), gauche (G), partially eclipsed (P, a CH3 eclipsing H) and fully eclipsed (F, CH3 eclipsing CH3) conforma... JEE Main level
• Sodium 3-methylbutanoate, (CH3)2CH-CH2-COONa, is heated with soda lime. The main organic product is: JEE Main level
• Assertion (A): The Wurtz reaction between two different primary alkyl halides is not a good method for making an unsymmetrical alkane. Reason (R): A mixture of ... JEE Main level
• Which of the following statements about free radical halogenation of alkanes are correct? (Use the bond dissociation energies: primary C-H 101 kcal/mol, seconda... JEE Main level
• An alkyl bromide R-Br is converted by the Wurtz reaction (Na, dry ether) into an alkane R-R. If R-R gives exactly two constitutional monochlorination products, ... JEE Advanced level
• Aqueous sodium propanoate (CH3CH2COONa, molar mass 96 g mol^-1) 19.2 g is electrolysed in a Kolbe synthesis. The alkane formed at the anode is obtained in 75\% ... JEE Advanced level
• Relative reactivity of C-H towards chlorine radical is primary : secondary : tertiary = 1 : 3.8 : 5. The percentage of 2-chloro-2-methylbutane in the monochlori... JEE Advanced level
• Treat the energy costs of eclipsing interactions in butane as additive: H/H = 4.0, CH3/H = 6.0, CH3/CH3 = 11.0 kJ/mol. The fully eclipsed conformation (dihedral... JEE Advanced level
• In which of the following preparations is ethane formed as the alkane product? JEE Advanced level
• Which of the following C6H14 isomers give exactly three constitutional monochlorination products? JEE Advanced level
• Aqueous sodium succinate, NaOOC-CH2-CH2-COONa, is electrolysed (Kolbe conditions). The hydrocarbon formed at the anode is: JEE Advanced level
• Free radical bromination of optically pure (S)-3-methylhexane at the tertiary C-H, with Br2 and light, gives 3-bromo-3-methylhexane as: JEE Advanced level