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Zorluk: ZorAlkanals and Alkanones: Oxidation, Reduction, and Distinction Tests

An organic compound ZZ with the molecular formula C5H10OC_5H_{10}O gives a negative result with Tollen's reagent and does not form a yellow precipitate when warmed with iodine in sodium hydroxide solution. Upon reduction with lithium tetrahydridoaluminate(III) (LiAlH4LiAlH_4), compound ZZ yields a secondary alkanol. Which of the following is the correct IUPAC name of compound ZZ?

  1. pentan-3-oneCevap
  2. B
    pentan-2-one
  3. C
    pentanal
  4. D
    3-methylbutan-2-one

Cevap

pentan-3-one
Pentan-3-one is an alkanone with the structure CH3CH2COCH2CH3CH_3CH_2COCH_2CH_3. Because it is a ketone, it cannot be oxidized by mild oxidizing agents like Tollen's reagent. Furthermore, because its carbonyl carbon is bonded to two ethyl groups rather than a methyl group, it gives a negative triiodomethane (iodoform) test. Reduction of pentan-3-one using LiAlH4LiAlH_4 yields pentan-3-ol, which is a secondary alkanol.

Adım Adım Çözüm

1
Analyze the functional group class using Tollen's reagent test.
Compound ZZ gives a negative Tollen's test, confirming it is an alkanone (ketone) rather than an alkanal (aldehyde).
Alkanals are easily oxidized to alkanoic acids and reduce Tollen's reagent to metallic silver, whereas alkanones resist mild oxidation.
2
Evaluate the iodoform (triiodomethane) test requirement.
The absence of a yellow precipitate (CHI3CHI_3) rules out compounds containing a methyl ketone (CH3CO−CH_3CO-) group.
Only methyl ketones (R−COCH3R-COCH_3) or ethanal (CH3CHOCH_3CHO) undergo triiodomethane formation with iodine in sodium hydroxide.
3
Examine the reduction reaction and identify the specific isomer.
Among the C5H10OC_5H_{10}O ketone isomers (pentan-2-one, pentan-3-one, and 3-methylbutan-2-one), only pentan-3-one lacks a methyl ketone group and reduces with LiAlH4LiAlH_4 to give pentan-3-ol (a secondary alkanol).
Pentan-3-one has the structural formula CH3CH2COCH2CH3CH_3CH_2COCH_2CH_3, fulfilling both qualitative test observations and structural reduction requirements.

Anahtar Kavram

Distinction tests for carbonyl compounds (Tollen's test and iodoform test) and reduction outcomes of alkanones
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Alkanals and Alkanones: Oxidation, Reduction, and Distinction Tests

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