Examkin

Soru

Zorluk: Çok zorAlkanals and Alkanones: Oxidation, Reduction, and Distinction Tests

An organic compound ZZ with the molecular formula C5H10OC_5H_{10}O gives a positive orange precipitate when treated with 2,4-dinitrophenylhydrazine. When warmed with acidified potassium heptaoxodichromate(VI) (K2Cr2O7K_2Cr_2O_7), compound ZZ is readily oxidized to a carboxylic acid containing five carbon atoms. Upon reduction with lithium tetrahydridoaluminate(III) (LiAlH4LiAlH_4), compound ZZ yields a primary alcohol that exhibits optical activity (chirality). What is the IUPAC name of compound ZZ?

  1. 2-methylbutanalCevap
  2. B
    pentan-2-one
  3. C
    pentanal
  4. D
    3-methylbutanal

Cevap

2-methylbutanal
2-methylbutanal has the molecular formula C5H10OC_5H_{10}O and contains an alkanal functional group. It reacts with 2,4-dinitrophenylhydrazine to form a precipitate. Because it is an alkanal, it undergoes oxidation with acidified potassium heptaoxodichromate(VI) to produce 2-methylbutanoic acid (a 5-carbon carboxylic acid). Upon reduction with lithium tetrahydridoaluminate(III), it forms 2-methylbutan-1-ol, which has an asymmetric carbon atom at position 2 bonded to four different substituent groups (−H-H, −CH3-CH_3, −CH2CH3-CH_2CH_3, −CH2OH-CH_2OH), rendering the molecule chiral and optically active.

Adım Adım Çözüm

1
Identify the functional group class from the 2,4-DNPH test.
A positive test with 2,4-dinitrophenylhydrazine confirms that compound ZZ is a carbonyl compound (either an alkanal or an alkanone).
Both alkanals and alkanones form colored hydrazone precipitates with 2,4-DNPH.
2
Distinguish between an alkanal and an alkanone using oxidation behavior.
Compound ZZ readily oxidizes with acidified K2Cr2O7K_2Cr_2O_7 to a carboxylic acid with 5 carbons, proving ZZ is an alkanal (pentanal isomer).
Alkanals are easily oxidized to carboxylic acids with the same number of carbon atoms, whereas alkanones resist oxidation under mild conditions.
3
Analyze the reduction product for chirality.
Reduction of an alkanal with LiAlH4LiAlH_4 yields a primary alcohol. Among 5-carbon alkanals (pentanal, 2-methylbutanal, 3-methylbutanal, 2,2-dimethylpropanal), only 2-methylbutanal reduces to 2-methylbutan-1-ol, CH3CH2CH(CH3)CH2OHCH_3CH_2CH(CH_3)CH_2OH.
In 2-methylbutan-1-ol, C-2 is bonded to four distinct groups: −H-H, −CH3-CH_3, −CH2CH3-CH_2CH_3, and −CH2OH-CH_2OH, making it a chiral molecule capable of optical isomerism.

Anahtar Kavram

Distinction between alkanals and alkanones via oxidation, reduction of carbonyls to alcohols, and optical isomerism in branched primary alcohols.
Bu soruyu puanla

Konular

Alkanals and Alkanones: Oxidation, Reduction, and Distinction Tests

Bu konudan daha fazla soru