Multiple Choice
Predict the major, organic product for the following reaction.
21. Aldehydes and Ketones: Nucleophilic Addition
DIBAL
5:20 minutesProblem 56d
Textbook Question
Show how you would synthesize octanal from each compound. You may use any necessary reagents.
(d) 1-bromoheptane
Verified step by step guidance1
Identify the target molecule (octanal) and the starting material (1-bromoheptane). Octanal is an aldehyde with an eight-carbon chain, while 1-bromoheptane is a seven-carbon alkyl halide. The goal is to add one carbon to the chain and introduce the aldehyde functional group.
Perform a nucleophilic substitution reaction to replace the bromine atom in 1-bromoheptane with a cyanide group (-CN). Use a reagent like sodium cyanide (NaCN) in a polar aprotic solvent (e.g., DMSO). This will yield heptanenitrile (C7H15CN).
Hydrolyze the nitrile group (-CN) in heptanenitrile to a carboxylic acid (-COOH). Use acidic hydrolysis (e.g., H2O, H2SO4, and heat) to convert the nitrile into heptanoic acid (C7H15COOH).
Perform a one-carbon homologation to extend the carbon chain by one carbon. Use a reagent like thionyl chloride (SOCl2) to convert heptanoic acid into heptanoyl chloride (C7H15COCl). Then, react heptanoyl chloride with diazomethane (CH2N2) to form an intermediate that rearranges to octanoic acid (C8H16O2).
Reduce the octanoic acid to octanal. Use a selective reducing agent like diisobutylaluminum hydride (DIBAL-H) at low temperature to reduce the carboxylic acid group (-COOH) to an aldehyde (-CHO), yielding octanal.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nucleophilic Substitution
Nucleophilic substitution is a fundamental reaction in organic chemistry where a nucleophile replaces a leaving group in a molecule. In the case of synthesizing octanal from 1-bromoheptane, a nucleophile such as a hydride ion (from a reducing agent like lithium aluminum hydride) can attack the carbon atom bonded to the bromine, leading to the formation of an alcohol intermediate that can be further oxidized to yield octanal.
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Oxidation-Reduction Reactions
Oxidation-reduction (redox) reactions involve the transfer of electrons between species, resulting in changes in oxidation states. In the synthesis of octanal, after converting 1-bromoheptane to an alcohol, the alcohol can be oxidized using reagents like potassium dichromate or PCC to form the aldehyde, octanal. Understanding the principles of oxidation is crucial for manipulating functional groups in organic synthesis.
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Functional Group Interconversion
Functional group interconversion refers to the transformation of one functional group into another, which is essential in organic synthesis. In this case, converting the alkyl bromide (1-bromoheptane) to an aldehyde (octanal) involves first converting the bromide to an alcohol and then oxidizing that alcohol. Mastery of these transformations allows chemists to design synthetic pathways to target molecules.
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