Chemistry Expert Q&A

When one compares the densities of n-hexane and water, one finds ________.

A) that n-hexane is less dense than water
B) that n-hexane is more dense than water
C) that these two compounds have the same density
D) that the relative densities of two immiscible compounds cannot be measured

Which of the halogens below undergoes free radical halogenation with ethane most rapidly?

A) fluorine
B) chlorine
C) iodine
D) bromine
E) pyridine

Consider the bond dissociation energies listed below in kcal/mol.
CH₃-Br 70
CH₃CH₂-Br 68
(CH₃) ₂CH-Br 68
(CH₃) ₃C-Br 65
These data show that the carbon-bromine bond is weakest when bromine is bound to a ________.

A) methyl carbon
B) primary carbon
C) secondary carbon
D) tertiary carbon
E) quaternary carbon

Given the pK_a values for the two acids below, what would you expect the K_eq for this reaction to be?

A) K_eq > 1
B) K_eq = 1
C) K_eq < 1
D) You can't tell from the information given.

Which of the statements below correctly describes an achiral molecule?

A) The molecule has a nonsuperimposable mirror image.
B) The molecule exhibits optical activity when it interacts with plane-polarized light.
C) The molecule has an enantiomer.
D) The molecule might be a meso form.
E) None of the above

Which of the following statements is the best statement of the Hammond Postulate?

A) In an endothermic reaction, the transition state is closer to the reactants in structure.
B) In an exothermic reaction, the transition state is closer in energy to the products.
C) Related species that are similar in energy are also similar in structure.
D) The structure of the transition state in an organic reaction is always modeled on the structure of the reactants leading to that transition state.
E) Transition states are molecular species of finite lifetime whose properties can be probed through free radical reactions.

Glucose has a specific rotation of +52.8°. Predict the concentration of a glucose aqueous solution contained in a 10 cm long polarimetry tube if a rotation of +15.8° was observed.

A) 0.299 g/mL
B) 0299 g/mL
C) 3.34 g/mL
D) 334 g/mL

Given the chlorination of acetone shown below, choose the correct rate law.
CH₃COCH₃ + Cl₂ → CH₃COCH₂Cl + HCl

A) rate = [CH₃COCH₃]
B) rate = [Cl₂]
C) rate = [CH₃COCH₃][Cl₂]
D) rate = [CH₃COCH₃][Cl₂]^1/2
E) cannot be determined from stoichiometry; must be determined experimentally

Which of the following statements correctly describes the contribution of to

A) The entropy term makes a greater contribution to ΔG° at low temperatures.
B) The entropy term makes a greater contribution to ΔG° at high temperatures.
C) The entropy term makes a greater contribution to ΔG° in exothermic reactions.
D) The entropy term makes a greater contribution to ΔG° in endothermic reactions.
E) The entropy term always makes a more significant contribution to ΔG° than does the enthalpy term.

A branched alkane has ________ boiling point relative to the isomeric linear alkane. There are ________ London force interactions in the branched alkane.

A) a higher; stronger
B) a higher; weaker
C) a lower, stronger
D) a lower; weaker
E) the same; similar

What term describes the structural relationship between (2R,3R,4S) -2,3,4-trichloroheptane and (2S,3S,4R) -2,3,4-trichloroheptane?

A) not isomers
B) constitutional isomers
C) enantiomers
D) diastereomers
E) conformers

Which of the following terms best describes the stereochemical relationship of the two compounds shown below in Fischer notation?

A) enantiomers
B) diastereomers
C) constitutional isomers
D) cis/trans - isomers
E) meso - same structure

If (S) -glyceraldehyde has a specific rotation of -8.7°, what is the specific rotation of (R) -glyceraldehyde?

A) 0.0°
B) -8.7°
C) +8.7°
D) cannot be determined from the information given

Which of the following depictions most closely resembles the structure of the transition state for the following acid-base reaction?

A)
B)
C)
D)

Which of the following intermediates is thought to occur in the mechanism by which alkenes are hydrated in the presence of acid?

A) carbanion
B) carbocation
C) free radical
D) carbene
E) alkyne

When propylene reacts with hydrogen bromide in the presence of a peroxide initiator, which of the following structures are formed during the mechanism?

A)
B)
C)
D) H∙

HBr can be added to an alkene in the presence of peroxides (ROOR) . What function does the peroxide serve in this reaction?

A) nucleophile
B) electrophile
C) radical chain initiator
D) acid catalyst
E) solvent

Which of the following statements is (are) true for the compound (3R, 4R) -3,4-dimethylhexane?

A) This compound is chiral.
B) The enantiomer of this compound is (3S, 4S) -3,4-dimethylhexane.
C) This compound is a diastereomer of (3R, 4S) -3,4-dimethylhexane.
D) all of the above
E) none of the above

What term describes the structural relationship between (2R,3R,4S) -2,3,4-trichloroheptane and (2R,3R,4R) -2,3,4-trichloroheptane?

A) not isomers
B) constitutional isomers
C) enantiomers
D) diastereomers
E) conformers

Consider the following substitution reaction with a ΔG° value of -91.1 kJ/mole.
HO- + CH₃Cl ↔ CH₃OH + Cl-
Given this information which of the following statements must be true? (R = 8.315 J/mole K)

A) The Keq at 25°C for this reaction is very large, in other words this reaction proceeds to near completion as written, left to right under standard conditions.
B) The Keq at 25°C for this reaction is very small (<1) , in other words this reaction does not proceed from left to right but rather is favored from right to left under standard conditions .
C) At 250°C the equilibrium concentration is shifted right in favor of the products (CH₃OH and Cl-) . In other words there is more product than at 25°C.
D) At 250°C the equilibrium concentration of products and reactants is nearly the same.
E) Both A and C are correct.