Organic Compounds Containing Halogens
- Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).Assertion (A) : (primary alkyl iodide drawn as zig-zag chain ending in I) undergoes S_N2 reaction faster than (the corresponding alkyl chloride,… Answer: 1. Both A and R are true and R is the correct explanation of A Key idea: in S_N2 the rate depends on how easily the leaving group de... 1
- The compound that will undergo S_N1 reaction with the fastest rate is Answer: 1. [structure: 1-bromoethylbenzene (phenyl-CH(CH ₃ )-Br), see figure] Key idea: S_N1 rate depends on carbocation stability. 1-Bromoe... 1
- The given compoundC_6H_5-CH=CH-CH(X)-CH_2CH_3 (benzene ring attached to CH=CH-CH(X)-CH_2CH_3)is an example of ________. Answer: 4. allylic halide Key idea: A halide is named by the carbon that carries the halogen. In C₆H₅-CH=CH-CH(X)-CH₂CH₃ , X is on an sp³ ca... 1
- The correct sequence of bond enthalpy of 'C–X' bond is : Answer: 2. CH₃-F > CH₃-Cl > CH₃-Br > CH₃-I Key idea: bond enthalpy decreases as the halogen gets larger (longer, weaker C-X bond). Bond leng... 1
- Identify compound X in the following sequence of reactions :Toluene (C_6H_5CH_3) Cl_2/h X [373\ K]H_2O Benzaldehyde (C_6H_5CHO) Answer: 3. Benzal chloride (C ₆ H ₅ CHCl ₂ ) Free-radical chlorination of the side chain ( Cl₂/hν ) replaces methyl hydrogens. To get an ald... 1
- Identify A and predict the type of reaction. [Reactant: 3-bromoanisole (benzene ring with OCH3 and Br meta to each other) with NaNH2 gives A] Answer: 4. [structure: 3-aminoanisole (OCH3 and NH2 meta)] and substitution reaction Key idea: aryl halide with NaNH₂ reacts through a benzy... 1
- Consider the reactionCH_3CH_2CH_2Br + NaCN → CH_3CH_2CH_2CN + NaBrThis reaction will be the fastest in Answer: 2. N,N' -dimethylformamide (DMF) Key idea: this is an S_N2 reaction on a primary halide, which is fastest in a polar aprotic solvent... 1
- Which of the following compounds shall not produce propene by reaction with HBr followed by elimination or direct only elimination reaction? Answer: 2. H₂C=C=O Key idea: propene forms from a three-carbon alcohol or halide by elimination (or from cyclopropane by HBr ring opening to... 1
- For the following reactions :(a) CH_3CH_2CH_2Br + KOH → CH_3CH=CH_2 + KBr + H_2O(b) (CH3)2CHBr + KOH -> (CH3)2CHOH + KBr (structures shown in figure)(c) cyclohexene + Br_2 -> 1,2-dibromocyclohexane (structures shown in figure)Which of the following s… Answer: 2. (a) is elimination, (b) is substitution and (c) is addition reaction. Key idea: identify what happens to the substrate. (a) CH₃CH... 1