Using your roadmaps as a guide, show how to convert 4-methyl-1-pentene and carbon dioxide into 5 -methylhexanoic acid. You must use 4 -methyl-1-pentene and carbon dioxide as the source of all carbon atoms in the target molecule. Show all reagents and all molecules synthesized along the way. CC(C)CC=CC(=O)O CC(C)CCCC(=O)O 4-Methyl-1-pentene 5-Methylhexanoic acid

Hydroboration-oxidation is a two-step organic chemistry reaction that transforms alkenes into alcohols. The beauty of this reaction lies in its stereospecificity and regioselectivity, which means the result is predictable and the same each time. Initially, borane (BH3) adds across the double bond of the alkene in a process known as hydroboration. The boron atom bonds to the less substituted carbon, while hydrogen attaches to the more substituted carbon, ensuring anti-Markovnikov orientation. The importance of mentioning anti-Markovnikov is it guides us in selecting reagents when targeting a molecule with specific functional groups.
Then comes oxidation, where hydrogen peroxide (H2O2) and a base (like NaOH) are used to oxidize the boron, replacing it with a hydroxide group to yield the corresponding alcohol. One would use hydroboration-oxidation when needing to increase the length of the carbon chain, starting from an alkene, without disrupting the existing carbon structure.
In the context of synthesizing 5-methylhexanoic acid, hydroboration-oxidation turns the alkene, 4-methyl-1-pentene, into an alcohol. This alcohol, now featuring a reactive -OH group, sets the stage for the next steps in the chain elongation process.

Carbon dioxide (CO2), though a stable molecule, can be transformed into a reactive intermediate when approached correctly. In organic synthesis, carbon dioxide's reactivity can be harnessed by converting it into a carboxylate ion using a Grignard reagent. A Grignard reagent, like ethylmagnesium bromide (EtMgBr), is known for its strong nucleophilicity and its ability to attack electrophilic carbon atoms.
Upon treatment with CO2, the Grignard reagent adds to the carbon of CO2, forming a carboxylate anion. This newly formed carboxylate anion is a cornerstone in building complex molecules as it becomes a source of two carbon atoms that can link to existing molecules to elongate the carbon chain. The addition of a carboxylate ion is an essential step towards creating carboxylic acids, esters, and amides, which are fundamental functionalities in organic chemistry.
In our roadmap towards synthesizing 5-methylhexanoic acid, this step allows the addition of two carbon atoms derived from CO2 to the alcohol we obtained from hydroboration-oxidation, effectively extending our carbon chain.

Once we have successfully formed a carboxylate ion through the reaction of CO2 with a Grignard reagent, the next key step is the introduction of this ion into the growing molecule. The carboxylate ion is a versatile player that can react with various functional groups, including alcohols, to form different types of bonds.
During the carboxylate ion addition, the negatively charged oxygen of the carboxylate ion acts as a nucleophile, attacking the electrophilic carbon of the alcohol group from the hydroboration-oxidation step. Upon this nucleophilic attack, the carboxylate ion bonds with the alcohol, essentially connecting the CO2-derived two-carbon unit to the existing alcohol molecule. After the reaction, quenching with an aqueous acid, typically hydrochloric acid (HCl), results in the formation of the desired carboxylic acid.
In the final step of our synthesis of 5-methylhexanoic acid, the carboxylate ion from CO2 reacts with our alcohol derived from 4-methyl-1-pentene. The product of this addition is our target molecule, illustrating the power and versatility of the carboxylate ion in organic synthesis, particularly in chain extension reactions.