Section D: Multiple Choice Questions on Stereochemistry (25 Questions)
Q: What term describes molecules that are non-superimposable mirror images of each other? A) Diastereomers B) Constitutional isomers C) Enantiomers D) Conformers A: C) Enantiomers
Q: A chiral center is typically defined as a carbon atom bonded to: A) Three different groups B) Four different groups C) Two identical groups D) A double bond A: B) Four different groups
Q: Which of the following properties do enantiomers have in common? A) Direction of rotation of plane-polarized light B) Melting point C) Reactivity with a chiral reagent D) Solubility in a chiral solvent A: B) Melting point
Q: A compound that contains chiral centers but is achiral overall due to an internal plane of symmetry is called a: A) Racemic mixture B) Meso compound C) Diastereomer D) Conformer A: B) Meso compound
Q: What is the maximum number of stereoisomers for a compound with ‘n’ chiral centers (assuming no meso compounds)? A) n B) 2n C) n! D) 2^n A: D) 2^n
Q: Which convention is used to assign configuration (R or S) to chiral centers? A) Markovnikov’s Rule B) Zaitsev’s Rule C) Cahn-Ingold-Prelog (CIP) Rules D) Hofmann’s Rule A: C) Cahn-Ingold-Prelog (CIP) Rules
Q: A 50:50 mixture of two enantiomers is known as a: A) Meso mixture B) Diastereomeric mixture C) Racemic mixture D) Optically pure mixture A: C) Racemic mixture
Q: How do diastereomers differ from enantiomers? A) Diastereomers are mirror images, enantiomers are not. B) Diastereomers are superimposable, enantiomers are not. C) Diastereomers are non-superimposable, non-mirror image stereoisomers. D) Diastereomers have different molecular formulas. A: C) Diastereomers are non-superimposable, non-mirror image stereoisomers.
Q: What instrument is used to measure the optical activity of a compound? A) Spectrometer B) Polarimeter C) Chromatograph D) Calorimeter A: B) Polarimeter
Q: If a compound rotates plane-polarized light clockwise, it is designated as: A) (R) B) (S) C) Dextrorotatory (+) D) Levorotatory (-) A: C) Dextrorotatory (+)
Q: Which of the following is NOT a type of stereoisomer? A) Enantiomer B) Diastereomer C) Conformational isomer D) Constitutional isomer A: D) Constitutional isomer
Q: The process of separating a racemic mixture into its pure enantiomers is called: A) Resolution B) Racemization C) Inversion D) Epimerization A: A) Resolution
Q: What is the relationship between (2R,3S)-2,3-dibromobutane and (2S,3R)-2,3-dibromobutane? A) Identical B) Enantiomers C) Diastereomers D) Meso compounds A: B) Enantiomers
Q: Which of the following conditions is necessary for a molecule to be chiral? A) It must contain a carbon-carbon double bond. B) It must have a plane of symmetry. C) It must be superimposable on its mirror image. D) It must not be superimposable on its mirror image. A: D) It must not be superimposable on its mirror image.
Q: How many chiral centers are present in 2-butanol? A) 0 B) 1 C) 2 D) 3 A: B) 1
Q: What is the relationship between cis-1,2-dichlorocyclopropane and trans-1,2-dichlorocyclopropane? A) Enantiomers B) Diastereomers C) Meso compounds D) Identical A: B) Diastereomers
Q: In a Fisher projection, the horizontal lines represent bonds: A) Pointing into the page B) Pointing out of the page C) In the plane of the page D) Rotating freely A: B) Pointing out of the page
Q: What is the specific rotation of a pure enantiomer if its racemic mixture has an observed rotation of 0°? A) 0° B) Cannot be determined C) Double the observed rotation of the mixture D) Half the observed rotation of the mixture A: B) Cannot be determined (the specific rotation refers to the rotation of a pure enantiomer, not a mixture)
Q: Which of the following is true about meso compounds? A) They are optically active. B) They have no chiral centers. C) They are superimposable on their mirror image. D) They rotate plane-polarized light. A: C) They are superimposable on their mirror image.
Q: The reaction of a non-chiral reagent with a racemic mixture will produce: A) A single enantiomer B) A single diastereomer C) A racemic mixture of products D) A meso compound A: C) A racemic mixture of products
Q: What is the term for stereoisomers that can be interconverted by rotation around single bonds? A) Enantiomers B) Diastereomers C) Conformational isomers (conformers) D) Geometric isomers A: C) Conformational isomers (conformers)
Q: Which of the following molecules possesses a plane of symmetry? A) 2-chlorobutane B) Meso-tartaric acid C) (R)-2-butanol D) (S)-lactic acid A: B) Meso-tartaric acid
Q: A compound with a specific rotation of -10.5° is: A) Dextrorotatory B) Levorotatory C) Racemic D) Achiral A: B) Levorotatory
Q: What happens to the configuration of a chiral center during an S$_N$2 reaction? A) It is retained. B) It is inverted. C) It becomes racemic. D) It becomes a meso compound. A: B) It is inverted.
Q: How many chiral centers are present in cholesterol? (This requires external knowledge or an image, but assuming common knowledge of common organic molecules’ complexity) A) 0-2 B) 3-5 C) 6-8 D) More than 8 A: C) 6-8 (Cholesterol has 8 chiral centers)