IMAT - International Medical Admissions Fundamentals of Organic Chemistry Questions and Answers — Questions and Answers
Question 1: An alpha-amino acid is a fundamental building block of proteins. Which two functional groups are always attached to the alpha-carbon of a standard amino acid?
- A hydroxyl group and an ether group
- An amino group and a carboxyl group (Correct answer)
- An aldehyde group and a ketone group
- A sulfhydryl group and an amide group
Correct answer: An amino group and a carboxyl group
By definition, an alpha-amino acid has a central carbon atom (the alpha-carbon) bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable side chain (R group). The amino and carboxyl groups are the defining functional groups.
Question 2: A molecule is described as 'chiral' if it is non-superimposable on its mirror image. Which of the following molecules possesses a chiral center and is therefore a chiral molecule?
- 2-methylpropane
- 2-propanol
- 2-butanol (Correct answer)
- 2-methyl-2-propanol
Correct answer: 2-butanol
A chiral center is typically a carbon atom bonded to four different groups. In 2-butanol (CH3-CH(OH)-CH2-CH3), the second carbon atom is bonded to a hydrogen (-H), a hydroxyl group (-OH), a methyl group (-CH3), and an ethyl group (-CH2CH3). Since all four groups are different, this carbon is a chiral center, making the molecule chiral. The other molecules have carbons bonded to at least two identical groups.
Question 3: A student is asked to arrange three organic compounds with similar molecular weights in order of increasing boiling point: pentane, butan-1-ol, and diethyl ether. Which of the following represents the correct order?
- Butan-1-ol < Diethyl ether < Pentane
- Diethyl ether < Pentane < Butan-1-ol
- Pentane < Butan-1-ol < Diethyl ether
- Pentane < Diethyl ether < Butan-1-ol (Correct answer)
Correct answer: Pentane < Diethyl ether < Butan-1-ol
Boiling point is determined by the strength of intermolecular forces. Pentane is a nonpolar alkane and only has weak London dispersion forces. Diethyl ether is a polar molecule and exhibits stronger dipole-dipole interactions. Butan-1-ol contains a hydroxyl (-OH) group, allowing it to form strong hydrogen bonds, which are the strongest of the three intermolecular forces present. Therefore, the order of increasing boiling point is Pentane < Diethyl ether < Butan-1-ol.
Question 4: A primary alcohol, such as ethanol (CH3CH2OH), is treated with a strong oxidizing agent like acidified potassium permanganate (KMnO4) and heated. What is the final major organic product of this reaction?
- Ethanal
- Ethene
- Ethanoic acid (Correct answer)
- Ethane
Correct answer: Ethanoic acid
Strong oxidizing agents like KMnO4 will oxidize a primary alcohol completely. The alcohol is first oxidized to an aldehyde (ethanal), but under these strong, aqueous conditions, the reaction does not stop there. The aldehyde is immediately further oxidized to a carboxylic acid (ethanoic acid).
Question 5: The molecule ethyne (C2H2), also known as acetylene, features a triple bond between its two carbon atoms. What is the hybridization of the carbon atoms in ethyne?
- sp (Correct answer)
- sp2
- sp3
- sp3d
Correct answer: sp
In ethyne, each carbon atom forms one sigma bond with a hydrogen atom and one sigma bond with the other carbon atom. The triple bond consists of this one sigma bond and two pi bonds. To accommodate two sigma bonds and achieve the observed linear geometry (180° bond angles), each carbon atom must be sp hybridized, using one s and one p orbital to form two sp hybrid orbitals. The remaining two p orbitals on each carbon are used to form the two pi bonds.
Question 6: Which of the following molecules is classified as aromatic?
- Cyclohexane
- Cyclohexene
- Benzene (Correct answer)
- Cyclobutadiene
Correct answer: Benzene
For a molecule to be aromatic, it must be cyclic, planar, fully conjugated, and satisfy Hückel's rule by having 4n+2 pi electrons (where n is a non-negative integer). Benzene (C6H6) is cyclic, planar, has a continuous ring of p-orbitals, and contains 6 pi electrons (where n=1 for the 4n+2 rule). Cyclohexane is non-planar and saturated. Cyclohexene is not fully conjugated. Cyclobutadiene is anti-aromatic because it has 4n (where n=1) pi electrons.
IMAT - International Medical Admissions Fundamentals of Organic Chemistry Questions and Answers
An alpha-amino acid is a fundamental building block of proteins.
Which two functional groups are always attached to the alpha-carbon of a standard amino acid?