Which of the following is the major organic product formed when 1-hexyne undergoes hydroboration–oxidation (using ${\mathrm{BH}}_3$ followed by $H{2}_O/\mathrm{OH}/H{2}_O{2}_{}$)?

• A. Hexanal (${\mathrm{CH}}_3-\mathrm{CH}-\mathrm{CH}-\mathrm{CH}-\mathrm{CH}-\mathrm{CHO}$)
• B. 2-Hexanone (${\mathrm{CH}}_3-\mathrm{CO}-\mathrm{CH}-\mathrm{CH}-\mathrm{CH}{3}_3$)
• C. Hexanoic acid (${\mathrm{CH}}_3-\mathrm{CH}-\mathrm{CH}-\mathrm{CH}-\mathrm{COOH}$)
• D. 1-Hexanol (${\mathrm{CH}}_3-\mathrm{CH}-\mathrm{CH}-\mathrm{CH}-\mathrm{CH}{2}_{}\mathrm{OH}$)

Answer: (A)

Verified step by step guidance

1. Identify the starting material: 1-hexyne is a terminal alkyne with the triple bond between the first and second carbon atoms.
2. Recall the hydroboration–oxidation reaction mechanism for alkynes: when a terminal alkyne undergoes hydroboration with BH\_3 followed by oxidation with H\_2O\_/OH\_/H\_2O\_2, the reaction proceeds via syn addition of boron and hydrogen across the triple bond, followed by oxidation to form an enol intermediate.
3. Understand the tautomerization step: the enol formed from the hydroboration–oxidation of a terminal alkyne rapidly tautomerizes to an aldehyde, not a ketone, because the boron adds to the less substituted carbon (anti-Markovnikov addition).
4. Write the expected product structure: since the boron adds to the terminal carbon, after oxidation and tautomerization, the product is an aldehyde with the carbonyl group at the terminal position, specifically hexanal.
5. Compare the options given: hexanal corresponds to the aldehyde product formed, while 2-hexanone is a ketone (from Markovnikov addition), hexanoic acid is an oxidized acid (not formed here), and 1-hexanol is an alcohol (not the product of this reaction).