OAT Organic Chemistry Practice Test 2024 Untimed [Explanation]

Last Updated on June 24, 2024

OAT Organic Chemistry Practice Test 2024 Untimed [Explanation]. Try our free Optometry Admission Test (OAT) Organic Chemistry online quiz for better OAT test prep. Organic Chemistry is integral to mastering the OAT’s Survey of Natural Sciences portion.

Organic Chemistry is the final section in the OAT’s Survey of Natural Sciences section. The organic chemistry in this section is best studied in order. Organic Chemistry section, making comfort with this content a critical OAT skill.

The final subtest of the Survey of Natural Sciences is Organic Chemistry. Questions 71–100 will assess your knowledge of reaction mechanisms, properties of molecules, stereochemistry, nomenclature, reactions, acids and bases, and aromatics.

OAT Organic Chemistry Practice Test 2024 [Untimed]

1. Which of the following tends to increase the melting point of a solid?

(A) Increasing molecular weight
(B) Decreasing polarity
(C) Increasing surface area
(D) I and II
(E) I and III

View Answer
Answer: (E) I and III Explanation: Increasing molecular weight and surface area typically lead to higher melting points due to stronger intermolecular forces.

2. Which of the following is the most stable conformation of cyclohexane?

(A) Boat
(B) Chair
(C) Half-chair
(D) Twist-boat
(E) Planar

View Answer
Answer: (B) Chair Explanation: The chair conformation is the most stable conformation of cyclohexane due to its minimized torsional strain and steric hindrance.

3. What type of isomerism exists between butane and isobutane?

(A) Structural isomerism
(B) Geometric isomerism
(C) Optical isomerism
(D) Conformational isomerism
(E) None of the above

View Answer
Answer: (A) Structural isomerism Explanation: Butane and isobutane are structural isomers because they have the same molecular formula but different structures.

4. Which of the following reagents can be used to convert an alcohol into an alkyl chloride?

(A) HCl
(B) SOCl2
(C) NaCl
(D) Cl2
(E) KCl

View Answer
Answer: (B) SOCl2 Explanation: Thionyl chloride (SOCl2) is commonly used to convert alcohols into alkyl chlorides via an SN2 reaction mechanism.

5. What is the major product of the reaction between 1-butene and HBr in the presence of peroxides?

(A) 1-bromobutane
(B) 2-bromobutane
(C) Butane
(D) 1,2-dibromobutane
(E) 2,3-dibromobutane

View Answer
Answer: (A) 1-bromobutane Explanation: In the presence of peroxides, HBr adds to alkenes via an anti-Markovnikov mechanism, resulting in the formation of 1-bromobutane.

6. Which of the following compounds is aromatic?

(A) Cyclohexane
(B) Benzene
(C) Cyclobutane
(D) Cyclooctatetraene
(E) Cyclopentadiene

View Answer
Answer: (B) Benzene Explanation: Benzene is aromatic because it satisfies Huckel’s rule (4n + 2 π electrons) and has a planar, cyclic structure with delocalized π electrons.

7. What is the hybridization of the carbon atoms in ethyne (acetylene)?

(A) sp
(B) sp2
(C) sp3
(D) sp3d
(E) sp3d2

View Answer
Answer: (A) sp Explanation: In ethyne, each carbon atom forms two sigma bonds and has two π bonds, leading to sp hybridization.

8. Which reagent is used to reduce a ketone to a secondary alcohol?

(A) H2/Pd
(B) NaBH4
(C) KMnO4
(D) O3
(E) Br2

View Answer
Answer: (B) NaBH4 Explanation: Sodium borohydride (NaBH4) is commonly used to reduce ketones to secondary alcohols.

9. What is the IUPAC name for the compound CH3CH2C≡CH?

(A) 1-butyne
(B) 2-butyne
(C) 1-pentyne
(D) 2-pentyne
(E) Butene

View Answer
Answer: (A) 1-butyne Explanation: The IUPAC name for CH3CH2C≡CH is 1-butyne, as the triple bond starts at the first carbon atom.

10. What type of reaction occurs when ethyl bromide is treated with KOH in ethanol?

(A) Substitution
(B) Elimination
(C) Addition
(D) Polymerization
(E) Rearrangement

View Answer
Answer: (B) Elimination Explanation: When ethyl bromide is treated with KOH in ethanol, an elimination reaction occurs, resulting in the formation of ethene.

11. Which of the following compounds has the highest boiling point?

(A) Methane
(B) Ethane
(C) Propane
(D) Butane
(E) Pentane

View Answer
Answer: (E) Pentane Explanation: Pentane has the highest boiling point among the given compounds due to its larger molecular size and increased van der Waals forces.

12. Which of the following is the correct order of acidity for the given compounds: acetic acid, ethanol, water, and phenol?

(A) Acetic acid > Phenol > Water > Ethanol
(B) Ethanol > Water > Phenol > Acetic acid
(C) Water > Ethanol > Phenol > Acetic acid
(D) Acetic acid > Water > Phenol > Ethanol
(E) Phenol > Acetic acid > Water > Ethanol

View Answer
Answer: (A) Acetic acid > Phenol > Water > Ethanol Explanation: Acidity order is determined by the stability of the conjugate base, with acetic acid being the most acidic and ethanol the least.

13. Which of the following compounds will react with Tollen’s reagent to give a positive result?

(A) Acetone
(B) Formaldehyde
(C) Benzene
(D) Ethanol
(E) Propane

View Answer
Answer: (B) Formaldehyde Explanation: Tollen’s reagent reacts with aldehydes to form a silver mirror, and formaldehyde is an aldehyde.

14. What is the product of the hydroboration-oxidation of 1-hexene?

(A) 1-hexanol
(B) 2-hexanol
(C) Hexane
(D) 3-hexanol
(E) 4-hexanol

View Answer
Answer: (A) 1-hexanol Explanation: Hydroboration-oxidation of 1-hexene follows an anti-Markovnikov addition, resulting in 1-hexanol.

15. Which of the following describes the hybridization of the nitrogen atom in ammonia (NH3)?

(A) sp
(B) sp2
(C) sp3
(D) sp3d
(E) sp3d2

View Answer
Answer: (C) sp3 Explanation: The nitrogen atom in ammonia is sp3 hybridized, with three sigma bonds and one lone pair of electrons.

16. What is the major product when 2-methyl-2-butene reacts with HCl?

(A) 2-chloro-2-methylbutane
(B) 3-chloro-2-methylbutane
(C) 2-chloro-3-methylbutane
(D) 1-chloro-2-methylbutane
(E) 1-chloro-3-methylbutane

View Answer
Answer: (A) 2-chloro-2-methylbutane Explanation: The reaction follows Markovnikov’s rule, where the hydrogen attaches to the carbon with more hydrogen atoms, forming 2-chloro-2-methylbutane.

17. Which of the following reagents is used in the Wittig reaction?

(A) Grignard reagent
(B) Ylide
(C) Peroxide
(D) Hydrogen gas
(E) Lithium aluminum hydride

View Answer
Answer: (B) Ylide Explanation: The Wittig reaction involves the use of an ylide to form alkenes from aldehydes or ketones.

18. Which of the following compounds is not chiral?

(A) 2-butanol
(B) 2-chlorobutane
(C) 2-methylbutane
(D) 3-chloropentane
(E) 3-methylhexane

View Answer
Answer: (C) 2-methylbutane Explanation: 2-methylbutane is not chiral because it does not have a carbon atom with four different substituents.

19. What is the IUPAC name for the compound with the formula (CH3)2C=CH2?

(A) 2-methylpropene
(B) 1-methylpropene
(C) 2-butene
(D) Isobutene
(E) 1-butene

View Answer
Answer: (A) 2-methylpropene Explanation: The IUPAC name for (CH3)2C=CH2 is 2-methylpropene.

20. What type of reaction is the formation of an ester from a carboxylic acid and an alcohol?

(A) Addition
(B) Substitution
(C) Elimination
(D) Condensation
(E) Polymerization

View Answer
Answer: (D) Condensation Explanation: The formation of an ester from a carboxylic acid and an alcohol is a condensation reaction, as it involves the loss of a small molecule (water).

21. Which of the following compounds is a meso compound?

(A) 2,3-dibromobutane
(B) 1,2-dibromoethane
(C) 2,3-dichloropentane
(D) 1,3-dibromobutane
(E) 1,2-dichlorobutane

View Answer
Answer: (A) 2,3-dibromobutane Explanation: 2,3-dibromobutane is a meso compound because it has a plane of symmetry and is optically inactive despite having chiral centers.

22. What is the product of the ozonolysis of 1-hexene?

(A) Hexane
(B) Hexanal
(C) Propanal
(D) 1-hexanol
(E) 2-butanone

View Answer
Answer: (B) Hexanal Explanation: Ozonolysis of 1-hexene cleaves the double bond and forms aldehydes, resulting in hexanal.

23. Which of the following best describes the inductive effect?

(A) The effect of electron delocalization
(B) The effect of steric hindrance
(C) The effect of electron withdrawal or donation through sigma bonds
(D) The effect of resonance
(E) The effect of hyperconjugation

View Answer
Answer: (C) The effect of electron withdrawal or donation through sigma bonds Explanation: The inductive effect is the transmission of electron density through sigma bonds due to electronegativity differences.

24. Which of the following compounds undergoes nucleophilic substitution most readily?

(A) Benzene
(B) Toluene
(C) Chlorobenzene
(D) Nitrobenzene
(E) Aniline

View Answer
Answer: (D) Nitrobenzene Explanation: Nitrobenzene undergoes nucleophilic substitution most readily due to the strong electron-withdrawing effect of the nitro group.

25. What is the major product when 1-bromopropane reacts with sodium ethoxide in ethanol?

(A) Propene
(B) 1-propanol
(C) Ethyl propanoate
(D) 2-propanol
(E) Ethane

View Answer
Answer: (A) Propene Explanation: Sodium ethoxide in ethanol promotes an E2 elimination reaction, resulting in the formation of propene.

26. Which of the following compounds will give a positive iodoform test?

(A) Methanol
(B) Ethanol
(C) 1-propanol
(D) 2-propanol
(E) Butanol

View Answer
Answer: (D) 2-propanol Explanation: 2-propanol gives a positive iodoform test because it contains a methyl ketone group that reacts with iodine to form iodoform.

27. Which of the following is a feature of E2 elimination reactions?

(A) The reaction involves a carbocation intermediate.
(B) The reaction is stereospecific and occurs in a single step.
(C) The reaction rate depends only on the concentration of the base.
(D) The reaction proceeds via a three-step mechanism.
(E) The reaction leads to the formation of a syn product.

View Answer
Answer: (B) The reaction is stereospecific and occurs in a single step. Explanation: E2 elimination reactions are stereospecific, occur in a single step, and require anti-periplanar geometry for the leaving group and hydrogen.

28. What is the major product when benzene reacts with acetic anhydride in the presence of AlCl3?

(A) Benzaldehyde
(B) Acetophenone
(C) Toluene
(D) Phenol
(E) Benzyl alcohol

View Answer
Answer: (B) Acetophenone Explanation: Benzene reacts with acetic anhydride in the presence of AlCl3 in a Friedel-Crafts acylation reaction to form acetophenone.

29. Which of the following is a characteristic of SN1 reactions?

(A) The reaction is stereospecific.
(B) The reaction occurs in a single step.
(C) The reaction rate depends only on the concentration of the nucleophile.
(D) The reaction involves the formation of a carbocation intermediate.
(E) The reaction proceeds via an anti mechanism.

View Answer
Answer: (D) The reaction involves the formation of a carbocation intermediate. Explanation: SN1 reactions involve a two-step mechanism with the formation of a carbocation intermediate.

30. Which of the following reagents can be used to oxidize a primary alcohol to a carboxylic acid?

(A) PCC
(B) NaBH4
(C) H2/Pd
(D) KMnO4
(E) LiAlH4

View Answer
Answer: (D) KMnO4 Explanation: Potassium permanganate (KMnO4) is a strong oxidizing agent that can oxidize primary alcohols to carboxylic acids.

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