ACS Stereochemistry

The spatial orientation of the atoms of a molecule is called its what?

A) constitution

B) configuration

C) handedness

D) composition

B) configuration

An object that has no element of symmetry is called what?

A) tetrahedral

B) achiral

C) symmetric

D) asymmetric

D) asymmetric

Stereoisomers differ from each other in what respect?

A) composition.

B) constitution

C) configuration

D) steric hindrance

C) configuration

Which of the following must be true for an optically active compound?

A) the molecular configuration is achiral

B) the molecular configuration is chiral

C) the compound is a racemic mixture of enantiomers

D) the molecular configuration must have two or more stereogenic centers

B) the molecular configuration is chiral

Enantiomers are?

A) stereoisomers having non-identical mirror image configurations

B) stereoisomers that do not have non-identical mirror image configurations

C) stereoisomers having a mirror plane of symmetry

D) achiral stereoisomers

A) stereoisomers having non-identical mirror image configurations

Which conformation of cyclohexane has a C3 axis of symmetry?

A) boat

B) twist boat

C) chair

D) envelope

C) chair

Hydration, by oxymercuation, of 3-methyl-1-butene gives 3-methyl-2-butanol.What is the observed rotation of this product, using a 20% solution in ethanol in a 1dm polarimeter cell?.Assume the specific roatation of the pure (S)-enantiomer to be +16º

A) +3.2º

B) -3.2º

C) 180º (+ or -)

D) 0º

D) 0º

Consider the Fischer projection formula for (S)-2-chlorobutaneWhich of the following changes does not convert this structure to the (R)-enantiomer?

A) rotation 180º in the plane of the paper (or screen)

B) flipping the structure over (a 180º rotation out of the plane)

C) exchanging the two vertical substituents (i.e. top and bottom)

D) exchanging the two horizontal substituents (i.e. right and left)

A) rotation 180º in the plane of the paper (or screen)

Designate the CIP priority order of the following C5H11- groups. (Lowest < Highest priority order)I CH3(CH2)4- II (CH3)3CCH2- III C3H7CH(CH3)- IV (CH3)2CHCH2CH2-

A) I < II < III < IV

B) IV < III < II < I

C) I < IV < II < III

D) III < II < IV < I

C) I < IV < II < III

When HOBr adds to 4-methylcyclopentene, how many new stereogenic centers are formed?

A) 1

B) 2

C) 3

D) 4

C) 3

Which of the following isomeric dienes is chiral?

A) 2,3-pentadiene

B) 3-methyl-1,2-butadiene

C) 2-methyl-1,3-butadiene

D) none, all are achiral

A) 2,3-pentadiene

Two equivalents of bromine add to one equivalent of 1,7-octadiene. How many stereoisomeric tetrabromides will be formed?

A) 1

B) 2

C) 3

D) 4

C) 3

Two equivalents of OsO4 hydroxylate one equivalent of 1,5-cyclooctadiene. How many stereoisomeric cyclooctane-1,2,5,6-tetraols will be formed?

A) 1

B) 2

C) 3

D) 4

B) 2

The optically active bromohydrin (1R, 2R)-2-bromocyclohexanol reacts with base to produce cyclohexene oxide (C6H10O). Which of the following statements is true?

A) a racemic product is formed

B) the observed optical rotation changes sign

C) the observed optical rotation does not change sign

D) the product is achiral

D) the product is achiral

Pure (S)-2-butanol has a specific rotation of +13.52 degrees.You have made and purified a sample that has a calculated specific rotation of +6.76 degrees.What can you conclude about this sample?

A) the sample has completely racemized

B) 50% the sample has rearranged into a meso isomer

C) 50% of the sample has racemized

D) 75% of the sample has racemized

C) 50% of the sample has racemized

How many stereoisomers of (CH3)2CHCH=CHCH2CH(OH)CH2Br are possible?

A) 2

B) 3

C) 4

D) 5

C) 4

f two isomers have been classified correctly as epimers, they may also be called...?

A) diastereomers

B) enantiomers

C) tautomers

D) conformers

A) diastereomers

The drawing on the right shows that cis-1,2-dichlorocyclohexane is chiral.Efforts to resolve this compound fail. Why?

A) the cis and trans isomers rapidly interconvert.

B) the compound is actually a meso structure.

C) the chair conformers rapidly interconvert producing a racemic mixture.

D) methods for resolving alkyl chlorides are not available.

C) the chair conformers rapidly interconvert producing a racemic mixture.

Which of the following statements must be true for two pure chiral isomers ?

A) they must be enantiomers

B) they must be diastereomers

C) they must be stereoisomers

D) they must be optically active

D) they must be optically active

Which of the following statements is true for a pair of diastereomers? A) they will have identical physiological properties.

B) they will have specific rotations of opposite sign.

C) they will have identical chemical properties (e.g. reactivity)

D) they will have different physical properties.

D) they will have different physical properties.

Which of the following descriptive terms would never be applied to a pair of stereoisomers ?

A) enantiomers

B) tautomers

C) diastereomers

D) epimers

B) tautomers

What kind of reagent would be needed to resolve a racemic amine, such as 2-aminobutane ?

A) the pure optically active amine to serve as a template for crystallization.

B) an achiral carboxylic acid to give a racemic mixture of amine salts.

C) an enantiomerically pure chiral carboxylic acid to give a diastereomeric mixture of amine salts.

D) a racemic chiral carboxylic acid to give a complete mixture of isomeric amine salts.

C) an enantiomerically pure chiral carboxylic acid to give a diastereomeric mixture of amine sal

What common symmetry elements if any are found in the stable chair conformer of trans-1,4-dichlorocyclohexane?

A) a single mirror plane and a C2 rotational axis.

B) a C3 rotational axis but no mirror plane.

C) two orthogonal mirror planes and a C2 rotational axis.

D) a single C2 rotational axis but no mirror plane.

A) a single mirror plane and a C2 rotational axis.

What common symmetry elements if any are found in the stable chair conformer of trans-1,2-dichlorocyclohexane?

A) a single mirror plane and a C2 rotational axis.

B) a single mirror plane and a C3 rotational axis.

C) two orthogonal mirror planes and a C2 rotational axis.

D) a single C2 rotational axis but no mirror plane.

D) a single C2 rotational axis but no mirror plane.

Reaction of 3-methyl-1,4-cycloheptadiene with excess perbenzoic acid (C6H5CO3H) forms a diepoxide product. How many stereoisomers, counting enantiomers, are expected from this reaction ?

A) 4 (two pairs of enantiomers)

B) 4 (two meso compounds and a pair of enantiomers)

C) 5 (two pairs of enantiomers and a meso compound)

D) 6 (two pairs of enantiomers and two meso compounds)

B) 4 (two meso compounds and a pair of enantiomers)

The antimalarial alkaloid quinine, C20H24N2O2, is optically active.An ethanol solution of 8g quinine in 100mL displays a rotation of -13.6º in a 1dm polarimeter tube.What is the specific rotation of quinine?

A) -85º

B) -170º

C) -43º

D) -26º

B) -170º

Which of the following compounds has a prochiral methylene group (i.e. the hydrogen atoms are diastereotopic)?

A) propane , CH3CH2CH3

B) cyclopropane , (CH2)3

C) 2-methylpropene , CH2=C(CH3)2

D) ethanol , CH3CH2OH

D) ethanol , CH3CH2OH

The thermal electrocyclic closure of (2E,4Z,6E)-2,4,6-octatriene gives which of the following?

A) cis-5,6-dimethyl-1,3-cyclohexadiene

B) trans-5,6-dimethyl-1,3-cyclohexadiene

C) cis-3,6-dimethyl-1,4-cyclohexadiene

D) cis-3,6-dimethyl-1,4-cyclohexadiene

A) cis-5,6-dimethyl-1,3-cyclohexadiene

The Cope rearrangement, [3,3]-sigmatropic shift, of meso-3,4-dimethyl-1,5-hexadiene gives which of the following?

A) 1,7-octadiene

B) (2Z,6Z)-2,6-octadiene

C) (2E,6Z)-2,6-octadiene

D) (2E,6E)-2,6-octadiene

C) (2E,6Z)-2,6-octadiene

Which of the following statements is not an essential feature of an optically active compound?

A) the molecules of an optically active compound will be dissymetric or asymmetric.

B) the molecules of an optically active molecule must have at least one stereogenic site.

C) an optically active compound's molecular configuration will not be identical with its mirror image.

D) an optically active compound will have at least one stereoisomer.

B) the molecules of an optically active molecule must have at least one stereogenic site.

Which of the following statements is not correct?

A) a pair of enantiomeric compounds will have the same melting point.

B) a pair of enantiomeric compounds will have the same solubility in ethanol.

C) a pair of enantiomeric compounds will have exactly the same functional groups.

D) a pair of enantiomeric compounds will have identical optical rotations.

D) a pair of enantiomeric compounds will have identical optical rotations.