ENADE Química Practice Questions - ENADE Química - Exame Nacional de Desempenho dos Estudantes Exam - ENADE Química Practice Questions - ENADE Química - Exame Nacional de Desempenho dos Estudantes Exam

Question 1

In a nucleophilic aliphatic substitution reaction, (2R)-2-bromobutane is treated with sodium cyanide (NaCN) in dimethyl sulfoxide (DMSO) at room temperature. What is the primary IUPAC product and the stereochemical outcome of this transformation?

(2R)-2-methylbutanenitrile via retention of configuration (2S)-2-bromobutane via carbocation racemization (2S)-2-methylbutanenitrile via complete inversion of configuration A 50:50 racemic mixture of (2R)- and (2S)-2-methylbutanenitrile

Correct Answer:

(2S)-2-methylbutanenitrile via complete inversion of configuration

Question 2

When 2-bromo-2-methylbutane is treated with potassium tert-butoxide (t-BuOK) in tert-butanol under reflux, the major elimination product formed is 2-methyl-1-butene rather than 2-methyl-2-butene. Which mechanistic rationale explains this regiochemical preference?

Steric hindrance of the bulky tert-butoxide base restricts deprotonation to the more accessible methyl protons, yielding the less substituted Hofmann alkene. The bulky base destabilizes the anti-periplanar transition state required for the Hofmann product, forcing formation of the thermodynamic alkene. The reaction proceeds via a free carbocation E1 mechanism where hyperconjugation stabilizes the primary alkyl radical. Potassium tert-butoxide undergoes unimolecular conjugate addition, favoring the Zaitsev thermodynamic product at elevated temperatures.

Correct Answer:

Steric hindrance of the bulky tert-butoxide base restricts deprotonation to the more accessible methyl protons, yielding the less substituted Hofmann alkene.

Question 3

In an electrophilic aromatic substitution (SEAr), acetanilide undergoes mononitration using HNO3/H2SO4 significantly faster than nitrobenzene and yields predominantly para-nitroacetanilide. What explains the activating and directing property of the acetamido group (-NHCOCH3)?

The carbonyl group donates electron density inductively into the aromatic ring, making all positions equally reactive. The nitrogen atom withdraws electron density by resonance, directing substitution selectively to the meta position. The acetamido group forms a cyclic benzyne intermediate that undergoes nucleophilic addition at the para position. The lone pair on nitrogen delocalizes into the π-system of the benzene ring by resonance (+R effect), stabilizing ortho/para arenium ion intermediates.

Correct Answer:

The lone pair on nitrogen delocalizes into the π-system of the benzene ring by resonance (+R effect), stabilizing ortho/para arenium ion intermediates.

Question 4

Consider the crossed Aldol condensation between benzaldehyde (C6H5CHO) and acetone (CH3COCH3) catalyzed by aqueous sodium hydroxide (Claisen-Schmidt reaction). What is the major final condensation product formed after dehydration?

1,3-Diphenylpropane-1,3-dione 4-Phenylbut-3-en-2-one (benzalacetone) 2-Methyl-3-phenylpropan-1-ol 3-Hydroxy-3-phenylpropanoic acid

Correct Answer:

4-Phenylbut-3-en-2-one (benzalacetone)

Question 5

Which of the following isomeric dimethylcyclohexanes possesses a non-superimposable mirror image and is therefore optically active (chiral) in its most stable conformation?

cis-1,4-Dimethylcyclohexane cis-1,2-Dimethylcyclohexane trans-1,2-Dimethylcyclohexane trans-1,4-Dimethylcyclohexane

Correct Answer:

trans-1,2-Dimethylcyclohexane

Question 1

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Prepare with the ENADE Química Practice Questions - ENADE Química - Exame Nacional de Desempenho dos Estudantes Exam practice quiz. This question bank includes 100 questions covering reaction, energy, standard, solution, and water. Use it to review important concepts, identify knowledge gaps, and build confidence for the related exam, course, or assessment.

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ENADE Química Practice Questions - ENADE Química - Exame Nacional de Desempenho dos Estudantes Exam

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